Showing papers in "Archives of Civil and Mechanical Engineering in 2020"
TL;DR: In this article, the deformation-induced martensitic transformation, the transformation-induced plasticity (TRIP) effect, and the reversion annealing in the metastable austenitic stainless steels are reviewed.
Abstract: Recent progress in the understanding of the deformation-induced martensitic transformation, the transformation-induced plasticity (TRIP) effect, and the reversion annealing in the metastable austenitic stainless steels are reviewed in the present work. For this purpose, the introduced methods for the measurement of martensite content are summarized. Moreover, the austenite stability as the key factor for controlling the austenite to martensite transformation is critically discussed. This is realized by analyzing the effects of chemical composition, initial grain size, applied strain, deformation temperature, strain rate, and deformation mode (stress state). For instance, the effect of initial grain size is found to be complicated, especially in the ultrafine grained (UFG) regime. Furthermore, it seems that there is a critical grain size for changing the trend of α′-martensite formation. Decreasing the deformation temperature motivates the formation of α′-martensite, but there is a critical temperature for achieving the maximum tensile ductility. Afterwards, the modeling techniques for the transformation kinetics and the contribution of deformation-induced martensitic transformation to the strengthening of material and also strength-ductility trade-off are critically surveyed. The processing of UFG microstructure during reversion annealing, the effects of the recrystallization of the retained austenite, the martensitic shear and diffusional reversion mechanisms, and the annealing-induced martensitic transformation are also summarized. Accordingly, this overview presents the opportunities that the strain-induced martensitic transformation can offer for controlling the microstructure and mechanical properties of metastable austenitic stainless steels.
110 citations
TL;DR: This paper fills a gap in the literature as it addresses a new aspect of 3D printing, which is risk, and also discusses and categorizes the benefits, challenges, and risks of3D printing in construction.
Abstract: This paper provides a critical review of the related literature on 3D printing in construction. The paper discusses and evaluates the different 3D printing techniques in construction. The paper also discusses and categorizes the benefits, challenges, and risks of 3D printing in construction. The use of 3D printing technology offers several advantages over traditional methods. However, it comes with its own additional challenges and risks. The main benefits of 3D printing in construction include constructability and sustainability benefits. The challenges are categorized into seven groups. The main challenges, found through the literature, are material related. The most cited challenges are material printability, buildability, and open time. Additionally, scalability, structural integrity, and lack of codes and regulations are frequently cited as major challenges. The additional risks are categorized into seven groups: 3D printing material, 3D printing equipment, construction site, and environment, management, stakeholders, regulatory and economic, and cybersecurity risks. The paper fills a gap in the literature as it addresses a new aspect of 3D printing, which is risk. The paper also provides some insights, recommendations, and future research ideas.
81 citations
TL;DR: In this article, a series of uniaxial compression tests were conducted on non-persistently jointed rock specimens with double circular holes and the results indicated that the existence of nonpersistent joints has a significant influence on the strength characteristics of the specimens.
Abstract: To better understand the mechanical behavior in a jointed rock mass, a series of uniaxial compression tests were conducted on non-persistently jointed rock specimens with double circular holes. Acoustic emission (AE) and digital image correlation (DIC) techniques were applied to capture micro-crack events and real-time strain field evolution in the specimens. The results indicate that the existence of non-persistent joints has a significant influence on the strength characteristics of the specimens. Specifically, peak strength decreases at first and reaches a minimum at 30° then increases with increase in the joint dip angle. DIC technology has successfully monitored the development of surface strain fields. The fracture evolution process is comprehensively understood. Every sudden change in a strain field is usually accompanied by apparent AE events and stress–strain curves take the form of oscillations. The crack coalescence modes among joints can be summarized as six types and the crack coalescence patterns around holes and joints can be divided into three categories. These results are helpful to understanding further the mechanical properties and fracture mechanism of openings in non-persistently jointed rock masses.
72 citations
TL;DR: In this paper, an analytical design method for ductile tunnel linings is performed and an analytical prediction for the behavior of ductile tunnelling is provided, based on the principle of equivalent deformation of shotcrete linings with yielding elements.
Abstract: Ductile linings have been proved to be highly effective for tunnelling in heavy squeezing grounds. But there still has not been a well-established design method for them. In this paper, an investigation on an analytical design method for ductile tunnel linings is performed. Firstly, a solution in closed form for ground response of a circular tunnel within Burgers viscoelastic rocks is derived, accounting for the displacement release effect. Then based on the principle of equivalent deformation, the mechanical model of segmental shotcrete linings with yielding elements is established using the homogenization approach. Analytical prediction for behaviour of ductile tunnel linings is provided. Furthermore, the proposed design method for ductile tunnel linings is applied in Saint Martin La Porte access tunnel and the analytical prediction is in good agreement with field monitoring data. Finally, a parametric investigation on the influence of yielding elements on performance of ductile tunnel linings is conducted. Results show that the length of yielding elements poses a great influence on linings. It is feasible and effective to increase the length of yielding elements to obtain the pressure within the bearing capacity of linings. However, yield stress of yielding elements does not significantly affect the performance of the lining. It is suggested to apply yielding elements with relatively higher yield stress in linings for higher stability.
65 citations
TL;DR: In this article, a review of the use of laser powder bed fusion (L-PBF) for processing magnesium alloys as an alternative way to conventional technologies to manufacture parts in the aerospace industry is presented.
Abstract: Selective Laser Melting (SLM) of magnesium alloys is the technology undergoing dynamic development in many research centres. The results are promising and make it possible to manufacture defect-free material with better properties than those offered by the manufacturing technologies used to date. This review aims to evaluate present state as well as main challenges of using Laser Powder Bed Fusion (L-PBF) for processing magnesium alloys as an alternative way to conventional technologies to manufacture parts in the aerospace industry. This literature review is the first one to outline information concerning the potential to use magnesium alloys in the aerospace industry as well as to summarise the results of magnesium alloy processing using AM technologies, in particular L-PBF. The available literature was reviewed to gather information about: the use of magnesium alloys in the aerospace industry—the benefits and limitations of using magnesium and its alloys, examples of applications using new processing methods to manufacture aerospace parts, the benefits and potential of using L-PBF to process metallic materials, examples of the use of L-PBF to manufacture aerospace parts, and state-of-the-art research into L-PBF processing of magnesium and magnesium alloys.
63 citations
TL;DR: In this paper, five concrete mixtures with different replacement rates of lightweight ceramsite sand to silica sand are prepared for extrusion-based 3D printability evaluation and three different types of interior hollow structures are designed and 3D printed based on the optimized lightweight mixture.
Abstract: A practical revolution in construction could be realized by combining the potential of 3D concrete printing with lightweight cementitious materials to fabricate adeptly hollow structures. In this study, five concrete mixtures with different replacement rates of lightweight ceramsite sand to silica sand are prepared for extrusion-based 3D printability evaluation. To reduce the water absorption induced shrinkage and micro-cracks, the ceramsite sands were coated with polyvinyl alcohol. An optimized cementitious material was identified by harmonizing the fresh properties to the continuous printing process. Cubic and beam elements with four different types of interior hollow structures were designed and 3D printed based on the optimized lightweight mixture. The interior structures include cellular-shaped structure, truss-like structure, lattice-shaped structure with a square topology, as well as gridding shaped structure with triangle topology. The mechanical capacities of the printed samples were measured and evaluated by compressive tests for the cubic samples and four-points flexural bending tests for the beam specimens. Basing on the results, the rectangular lattice hollow structure demonstrates the best mechanical resistance to compression and the truss-shaped prism structure ensues the highest flexural properties. The stress distribution and failure process were also explored through discrete element method.
47 citations
TL;DR: In this paper, a nonlinear large-amplitude free vibration response of nanoshells prepared from functionally graded porous materials (FGPM) is investigated by taking into account surface stress size effects and vibrational mode interactions.
Abstract: At nanoscale, surface free energies of the atoms located on the free surfaces of structures significantly affect their mechanical characteristics. In this study, nonlinear large-amplitude free vibration response of nanoshells prepared from functionally graded porous materials (FGPM) is investigated by taking into account surface stress size effects and vibrational mode interactions. Non-classical shell model is constructed on the basis of the Gurtin–Murdoch type of the surface theory of elasticity having the capability of capturing surface stress size dependency. The accuracy of nonlinear vibration analysis is improved by incorporating the interaction of the main vibration mode and the first, third and fifth symmetric oscillation modes. Moreover, the closed-cell Gaussian-Random field scheme is put to use to extract the mechanical characteristics of FGPM nanoshell. Multiple timescales technique is then applied to achieve surface stress elastic-based nonlinear frequency of FGPM nanoshell analytically for different interactions between vibrational modes. It is revealed that by incorporating the interactions of the main vibration mode and higher symmetric oscillation modes, the behavior of the backbone curves belongs to the nonlinear free oscillation response of FGPM nanoshells changes from hardening to softening schema. It is found that when only the main vibration mode is taken into account, surface elasticity effects makes an enhancement in the significance of the hardening schema. However, by considering the interactions of higher symmetric oscillation modes, surface elasticity effects makes a reduction in the significance of the softening schema.
45 citations
TL;DR: In this article, a review of the processing routes to obtain the ferritic-martensitic microstructures, parameters of intercritical annealing (IA) treatment, primary thermomechanical treatments, and post processing of dual phase (DP) steels is presented.
Abstract: New concepts proposed for processing of dual phase (DP) steels as one of the main classes of advanced high-strength steels (AHSSs) to enhance their mechanical properties (strength–ductility combination) and corrosion resistance were introduced. The current review covers (I) the processing routes to obtain the ferritic–martensitic microstructures, (II) parameters of intercritical annealing (IA) treatment, (III) primary thermomechanical treatments, and (IV) post processing. First, the principal heat treatment methods, i.e., step quenching, intermediate quenching, and intercritical annealing of ferritic–pearlitic steel, as well as the partitioning of manganese were critically discussed. Then, the effects of holding time at the intercritical annealing temperature on the austenitization, grain coarsening kinetics, abnormal grain growth, and volume fraction of martensite were summarized. Next, the importance of cold deformation (notably rolling) and heating rate for the development of fine-grained DP microstructures (with chain-networked martensitic islands) through recrystallization and modification of the preferred nucleation sites for the austenite phase was discussed. Moreover, the applications of severe plastic deformation techniques (such as constrained groove pressing), thermal cycling (multi-step or repetitive intercritical annealing), and spheroidization heat treatment were discussed. Finally, the impacts of tempering, quench aging, and bake hardening on the properties of DP steel were reviewed. This short overview shows the opportunities that the conventional and innovative processing routes can offer for the potential industrial applications of DP steels, especially in the lightweight car body for the automotive industry to address the safety, fuel consumption, and air pollution issues.
43 citations
TL;DR: In this paper, a new constitutive model of saw-tooth joints was proposed based on Improved Harris function and laboratory shear tests, which can represent the trend of peak shear curve variation with higher accuracy, the parameters are easy to be solved and have obvious physical significance.
Abstract: The majority of jointed rock mass failures mainly occur along the joints in shear mode, which promotes a wide investigation on the proposal of a reasonable and reliable shear constitutive model of rock joints. In this paper, based on Improved Harris function and laboratory shear tests, a new constitutive model of saw-tooth joints was proposed. Firstly, a series of laboratory direct shear tests were carried out on saw-tooth joint specimens made of rock-like materials (cement mortar) to obtain the shear stress-displacement curves. Subsequently, the test results were divided into sliding failure type and peak shear type according to whether there is a significant stress drop between peak stress and residual stress. It is assumed that rock elements can be divided into undamaged parts and damaged parts during the shearing process. The stress-displacement relation of the undamaged part satisfies Hooke’s law, while the damaged part provides residual stress. Via the comparison with commonly used micro-element failure probability density functions, the Improved Harris distribution function was selected as the standard to characterize the strength of micro rock units. Finally, derived from the theory of damage statistical mechanics, a damage statistical constitutive model was proposed, which can reflect the deformation characteristics of rock joints. Compared with previous models and experimental data, the model proposed in this paper can represent the trend of peak shear curve variation with higher accuracy, the parameters are easy to be solved and have obvious physical significance, which verifies the advantages and applicability of this model.
37 citations
TL;DR: In this article, the authors proposed a new class of metal-polymer architected sandwich structures that exhibit different mechanical behaviors, which are made of aluminum face sheets and 3D-printed lattice cores with 2D (Bi-grid, Tri-grid), Quadri-grid and Kagome-grid topologies.
Abstract: In this article, we propose a new class of metal-polymer architected sandwich structures that exhibit different mechanical behaviors. These lightweight sandwich structures have been made of aluminum face sheets and 3D-printed lattice cores with 2D (Bi-grid, Tri-grid, Quadri-grid and Kagome-grid) and 3D (face-centered cubic-like and body-centered cubic-like) topologies. Finite element simulation and experimental tests were carried out to evaluate mechanical performances of the proposed sandwich structures under quasi-static three-point bending load. Specifically, the damage-tolerant capability, energy absorption and failure mechanisms of these sandwich structures were investigated and evaluated through a combination of analytical, numerical and experimental methods. It is found that sandwich structures with 3D face and body-centered cubic-like cores can provide more excellent flexural stiffness, strength and energy absorption performance. These enhanced mechanical features could be further explained by a so-called ‘Stress Propagation’ mechanism through finite element analysis (FEA) that can facilitate sandwich structures with 3D cores, especially body-centered cubic-like one, to transfer bending loads from central lattice units across neighboring ones more efficiently than 2D cores. Furthermore, core cracking is the main failure mode for the proposed sandwich structures, which is primarily caused and dominated by bending-induced tensile stress followed by shear stress. It is worth mentioning that our findings provide new insights into the design of novel lightweight sandwich composites with tailored mechanical properties, which can benefit a wide variety of high-performance applications.
28 citations
TL;DR: In this paper, the metallurgical behavior and mechanical properties of the P91 steel welds joint have been investigated and the relationship between mechanical behavior and microstructure of the welded joint has been evaluated for as-welded and heat treatment conditions.
Abstract: This paper investigates the metallurgical behavior and mechanical properties of the P91 steel welds joint. The joint of heat-resistant P91 steel has been welded by the gas tungsten arc welding (GTAW) process using the dissimilar Inconel grade 617 filler. The P91 welds joints have been subjected to varying heat treatment regimes in the temperature range of 650–810 °C for 2 h. The normalizing-based tempering was also performed for the welded joint. The weld fusion zone (WFZ) with austenitic structure and heat-affected zones (HAZs) with martensitic structure was characterized using the optical microscope and scanning electron microscope (SEM). The detailed characterization of the weld metal and HAZ interface has also been performed for as-welded and post-weld heat treatment (PWHT) conditions. For mechanical properties of the welds joint, tensile testing and hardness testing were performed. The relationship between mechanical behavior and microstructure of the welded joint has been evaluated for as-welded and heat treatment conditions. The microstructure studies revealed the formation of an unmixed zone (UZ) close to the fusion line, and it was characterized as peninsula and island. The WFZ showed the complete austenitic mode of the solidification and revealed the austenitic structure with cellular and equiaxed grains in the center of the weld metal. The columnar and cellular dendrites were seen near the boat fusion line, i.e., interface of the weld metal and HAZ. The soft δ ferrite patches were observed near the fusion line in the area of HAZ and remain undissolved up to tempering temperature of 810 °C (PW 3). The dissolution of the ferrite patches was noticed for PW 4. The maximum and minimum tensile strength of the welds joint was measured 731 MPa and 502 MPa for PW 3 and PW 2, respectively. A uniform hardness variation in the transverse direction of the welded joint was observed for PW 3 and PW 4 conditions. The optimum combination of strength and ductility was obtained for the PW 3 condition.
TL;DR: In this paper, a possible use of the guided waves in the estimation of the resistance of steel-concrete adhesive connection is studied, and the relationship relating adhesive connection resistance and wave propagation characteristics (wave velocity and the time of flight) have been derived and experimentally verified during pull-out tests conducted on a number of reinforced concrete beams varying in the debonding area.
Abstract: The development of the nondestructive diagnostic methods is of significant importance in the last decades. A special attention is paid to diagnostics of reinforced concrete structures, which are very popular in the civil engineering field. A possible use of the guided waves in the estimation of the resistance of steel–concrete adhesive connection is studied in the following paper. The relationships relating adhesive connection resistance and wave propagation characteristics (wave velocity and the time of flight) have been derived and experimentally verified during pull-out tests conducted on a number of reinforced concrete beams varying in the debonding area. The pull-out tests were also monitored ultrasonically. On the basis of the results in the form of the time-domain signals, the theoretical load-carrying capacities of the pulled-out bars have been calculated and compared with the exact experimentally determined values. The high agreement of the results obtained proved the correctness of the developed method. Moreover, the signals registered during pull-out tests allowed to observe the changes of the wave velocity induced by the deterioration of the adhesive connection.
TL;DR: In this paper, an innovative method for forming rail car axles by skew rolling in a CNC 3-roll mill was proposed. But the major shortcoming of the proposed method is the presence of chucking allowance.
Abstract: This study relates to an innovative method for forming rail car axles by skew rolling in a CNC 3-roll mill. The rolling mill was constructed at the Lublin University of Technology. The use of this machine makes it possible to produce elongated axisymmetric parts that are up to 55 mm in diameter and up to 1000 mm in length. Experimental rolling tests are performed (in 1:5 scale) using this machine. Two types of axles are analysed: one manufactured in accordance with North American standards (AAR Class E) and one manufactured in compliance with European standards (BA302). Diameters of produced axles have a dimensional accuracy of ± 0.4 mm. Produced axles are free from internal cracks, and their surface defects (shallow helical grooves) can easily be removed by machining. The major shortcoming of the proposed method is the presence of chucking allowance. To eliminate this allowance, it is proposed that the forming process should be performed in two operations: rolling extrusion and skew rolling. Results of a numerical analysis were performed using the Simufact.Forming program confirms that rail car axles can be formed by the proposed method.
TL;DR: In this paper, the higher-order modeling of a cylindrical nano-shell resting on Pasternak's foundation based on nonlocal elasticity theory is studied, and numerical results including lower-and higherorder longitudinal and radial displacements are presented in terms of nonlocal parameter.
Abstract: The aim of this present work is to study the higher-order modelling of a cylindrical nano-shell resting on Pasternak’s foundation based on nonlocal elasticity theory. Third-order shear deformation theory is developed for modelling the kinematic relations, and nonlocal elasticity theory is developed for size-dependent analysis. The principle of virtual work is applied to derive static governing equations. The solution is presented for simply supported boundary conditions in terms of various important parameters. The numerical results including lower- and higher-order longitudinal and radial displacements are presented in terms of nonlocal parameter, two parameters of Pasternak’s foundation and some dimensionless geometric parameters such as length-to-radius ratio and length-to-thickness ratio.
TL;DR: In this article, the effect of SiC particles content on microstructure, mechanical and wear behavior was investigated using the optical microscope, scanning electron microscopy and EDX analyses.
Abstract: In recent years, the composite materials have been very desirable by researchers for many engineering applications such as aviation and biomedical because of the tremendous characteristics of magnesium matrix metal composite. This current investigation aims to develop the AZ91/SiCp composites with various weight fractions (0, 2.5, 5 and 10 wt%) of silicon carbide particles via the stir casting method. The effect of SiC particles content on microstructure, mechanical and wear behaviour was investigated. The optical microscope, scanning electron microscopy and EDX analyses were utilized to detect the distribution of hard particles as well as the interface between the alloy and particles. Based on the findings, the homogeneous distribution of particles, refinement of grains in addition to good bonding between AZ91 alloy and particles have been achieved in produced composites. Therefore, the mechanical characteristics and wear performance are improved in composites compared with the unreinforced alloy. Moreover, these results suggest that for applications demanding high mechanical properties and wear resistance the AZ91/SiCp will be effective composites.
TL;DR: In this article, the authors investigated the performance of concrete beams reinforced with steel-FRP composite bar (SFCB) and showed that SFCB/hybrid reinforced specimens exhibited improved stiffness, reduced crack width and larger bending capacity compared with FRP-reinforced specimen.
Abstract: Flexural performance of concrete beams reinforced with steel–FRP composite bar (SFCB) was investigated in this paper. Eight concrete beams reinforced with different bar types, namely one specimen reinforced with steel bars, one with fiber-reinforced polymer (FRP) bars and four with SFCBs, while the last two with hybrid FRP/steel bars, were tested to failure. Test results showed that SFCB/hybrid reinforced specimens exhibited improved stiffness, reduced crack width and larger bending capacity compared with FRP-reinforced specimen. According to compatibility of strains, materials’ constitutive relationships and equilibrium of forces, two balanced situations, three different failure modes and balanced reinforcement ratios as well as analytical technique for predicting the whole loading process are developed. Simplified formulas for effective moment of inertia and crack width are also proposed. The predicted results are closely correlated with the test results, confirming the validity of the proposed formulas for practical use.
TL;DR: In this paper, the evolution of microstructure, texture and mechanical properties of AA 7075 alloy during equal channel angular pressing (ECAP) by route BC at room temperature at a pressing speed of 1 mm/min.
Abstract: In this article, an effort has been made to investigate the evolution of microstructure, texture and mechanical properties of AA 7075 alloy during equal channel angular pressing (ECAP) by route BC at room temperature at a pressing speed of 1 mm/min. Transmission electron microscopy (TEM) revealed the presence of rod-like (MgZn2) precipitates in annealed conditions which were broken after two ECAP passes along with remarkable grain refinement due to high imposed strain after the second pass. After two consecutive ECAP passes, hardness, yield strength, and tensile strength of the alloy increased significantly in comparison to initial annealed condition. The fraction of high angle boundaries (HABs) and grain misorientation angle significantly increased after ECAP passes compared to the initial condition. Texture measurements were performed by X-ray diffractometer (XRD), on TD plane (parallel to extrusion direction). Texture results revealed the dominance of $$C_{\theta }$$ and $$A_{2\theta }^{*}$$ components after the first pass and the presence of strong $$B_{\theta }$$, $$\bar{B}_{\theta }$$ and $$\bar{A}_{\theta }$$ components along with weaker $$A_{2\theta }^{*} ,\;C_{\theta }$$ components after the second pass. Scanning electron microscopy (SEM) revealed that the average dimple size was gradually reduced with increasing the ECAP passes.
TL;DR: In this paper, the friction spot extrusion welding process is successfully performed on dissimilar aluminum alloys of AA2024-T3 and AA6061-T6 under the influence of shoulder features.
Abstract: Friction spot extrusion welding process is successfully performed on dissimilar aluminum alloys of AA2024-T3 and AA6061-T6 under the influence of shoulder features. The joints were analysed by microstructural features and mechanical properties using conventional and advanced tools of visual inspection, optical microscopy, scanning electron microscopy, transmission electron microscopy, electron back scattered diffractions, tensile testing and hardness testing. The results revealed that the joining was obtained by combination of mechanical locking from extruded material of top surface to predrilled bottom surface and diffusion in solid state. The stir zone and plastically deformed metal flow zone were influenced by scroll shoulder and smooth shoulder features. The tensile specimen of scroll shoulder was resulted to higher fracture load of 6381 N whereas the same was 4916 N in case of smooth shoulder. The interface of between plastically deformed metal flow zone and base material of AA6061-T6 can be considered as critical/weakest zone in case of friction spot extrusion. The variations of hardness were observed in stir zone, plastically deformed metal flow zone and thermo-mechanically affected zone in case of friction spot extrusion welding process.
TL;DR: In this article, the results of experiments on deficient exterior reinforced concrete (RC) strong beam-weak column connections strengthened with carbon fiber-reinforced polymer (CFRP) sheets were reported.
Abstract: The current paper reports the results of experiments on deficient exterior reinforced concrete (RC) strong beam–weak column connections strengthened with carbon fiber-reinforced polymer (CFRP) sheets. Five RC-joint specimens with half-scale size were manufactured and tested subjected to constant axial and reversed cyclic quasi-static loads. These joints consisted of one control and four specimens retrofitted with FRP sheets used in different strengthening configuration. The study is mainly directed to the examination of the different anchoring methods for longitudinal FRPs at beam–column intersection including L-shaped anchorage or CFRP anchor fans as a modern anchorage technique. Furthermore, the efficiency of transverse CFRP sheets in the form of innovative corner strip-batten technique to improve the seismic performance of the weak column was compared with longitudinal sheets. The externally bonded reinforcement on grooves (EBROG) method was also used in all strengthening schemes to eliminate surface debonding of CFRP. Test results revealed that although all the retrofitting schemes used led to significant improvements of up to 80% in strength capacity, longitudinal FRP sheets applied through the EBROG method and anchored with CFRP fans were more effective in inducing a completely ductile behavior in the joints, while the plastic hinge was also relocated into the beam.
TL;DR: In this paper, the experimental performance of UHPSFRC beams subjected to loads at relatively low shear span-to-depth ratios was examined, and the results and observations from six tests provided a detailed insight into the ultimate response including shear strength and failure mode.
Abstract: This paper examines the experimental performance of ultra-high-performance steel fibre-reinforced concrete (UHPSFRC)
beams subjected to loads at relatively low shear span-to-depth ratios. The results and observations from six tests provide a detailed insight into the ultimate response including shear strength and failure mode of structural elements incorporating various fibre contents. The test results showed that a higher fibre content results in an increase in ultimate capacity and some
enhancement in terms of ductility. Detailed nonlinear numerical validations and sensitivity studies were also undertaken in order to obtain further insights into the response of UHPSFRC beams, with particular focus on the influence of the shear span-to-depth ratio, fibre content and flexural reinforcement ratio. The parametric investigations showed that a reduction
in shear span-to-depth ratio results in an increase in the member capacity, whilst a reduction in the flexural reinforcement ratio produces a lower ultimate capacity and a relatively more flexible response. The test results combined with those from numerical simulations enabled the development of a series of design expressions to estimate the shear strength of such
members. Validations were performed against the results in this paper, as well as against a collated database from previous experimental studies.
TL;DR: A compact compliant mechanism that enables in-principle straight-line parallel jaw motion is obtained, by combining the Scott–Russell mechanism and the parallelogram mechanism, for micro-manipulation applications.
Abstract: This paper presents the design, modeling, fabrication, and test of a monolithic compliant gripper for micro-manipulation applications A compact compliant mechanism that enables in-principle straight-line parallel jaw motion is obtained, by combining the Scott–Russell mechanism and the parallelogram mechanism The right-circular corner-filleted (RCCF) flexure hinge is adopted to achieve a large displacement of lumped-compliance joints A pseudo-rigid-body model (PRBM) method with the help of the virtual work principle is performed to obtain parametric analytical models including the amplification coefficient and kinetostatics Finite element analysis (FEA) is conducted to validate the analytical model and capture adverse parasitic motions of jaws A monolithic prototype was fabricated, the test results of which show satisfactory performances
TL;DR: In this article, six frost-damaged squat reinforced concrete (RC) shear walls were subjected to low cyclic reversal loading to investigate the effects of axial compression ratio, concrete strength and freeze-thaw cycles (FTCs) on the seismic performance of squat RC shear wall.
Abstract: In cold environment, the damage of freezing and thawing poses a great threat to the safety of concrete structures. In this study, six frost-damaged squat reinforced concrete (RC) shear walls were subjected to low cyclic reversal loading to investigate the effects of axial compression ratio, concrete strength and freeze-thaw cycles (FTCs) on the seismic performance of squat RC shear walls. The seismic behavior of the test specimens was evaluated in terms of the frost action at the microstructure level, frost-heave crack patterns, damage processes, failure patterns, hysteretic behaviors, skeleton curves, deformations, and energy dissipation capacities. It shows that the boundary elements and distributed reinforcements had obvious restraining effects on the development of frost-heave cracks. The FTC action weakened the load-carrying capacity, energy dissipation capacity, and shear resistance capacity of the walls. When the number of FTCs is kept at 200, with the increase of the concrete strength, the gel structure (C-S-H) gradually evolved from fibrous to nets, also the width and number of frost-heave cracks started to reduce, and the distribution of frost-heave cracks evolved from the middle of the specimen to the perimeter. Moreover, the energy dissipation capacity and the ratio of the shear displacement on the whole displacement after cracking loading condition started to increase.
TL;DR: In this paper, the effect of the material microstructure on the machining stability and tool wear behavior in dry drilling of the hard titanium alloys was investigated and the experimental results highlight a correlation between the tool wear behaviour and material microstructures.
Abstract: Additive Manufacturing (AM) technologies are increasingly applied in various industries since they provide the possibility to manufacture the components with high geometrical complexity easier and faster than traditional processes. However, the subsequent semi-finish/finish machining operations such as drilling, turning and/or milling are still necessary for AM parts to obtain the required surface textures and meet the practical requirements. As such, the AM parts usually indicate different machinability compared with conventionally produced ones in view of the different material microstructures. A comprehensive understanding of this machining effort is of great importance for similar engineering applications but not widely reported. Thus, an attempt was made in this work to address the effect of the material microstructure on the machining stability and tool wear behavior in dry drilling of the hard titanium alloys. The experimental results highlight a correlation between the tool wear behavior and material microstructures. A great number of micro-pits appeared on the tool flank face and the abrasive marks, coating delamination, as well as catastrophic failure of the cutting edge were found to be more obvious during machining the DMLS alloy. In contrast, adhesion wear followed by micro chipping and build-up edge were distinguished when machining the wrought Ti6Al4V. Meanwhile, heat treatment can improve the flow plasticity and reduce the brittleness of the AM material since catastrophic failure disappeared and chip adhesion becomes more predominant when machining the HTDMLS Ti6Al4V.
TL;DR: This study shows that ANN is a promising method for adequate classification of concrete as material resistant or not resistant to thermal explosive spalling.
Abstract: Explosive spalling is an unfavorable phenomenon observed in concrete when exposed to heating load. It is a great potential threat to safety of concrete structures subjected to accidental thermal loads. Therefore, assessing explosive spalling risk of concrete is important for fire safety design of concrete structures. This paper proposed a popular machine learning approach, i.e., artificial neural network (ANN), to assess explosive spalling risk of concrete. Besides, the decision tree method was also used to execute the same mission for a comparison purpose. Twenty-eight groups of heating tests were conducted to validate the proposed ANN model. The ANN model behaved well in assessing explosive spalling of concrete, with a prediction accuracy of 82.1%. This study shows that ANN is a promising method for adequate classification of concrete as material resistant or not resistant to thermal explosive spalling.
TL;DR: In this paper, the transverse groove springs are designed and the isolator prototype is assembled, and the experimental results clearly show the good isolation performance of the QZS isolator and meanwhile reflect some practical factors that should be noticed in actual applications.
Abstract: The concept of quasi-zero-stiffness (QZS) vibration isolator was proposed in recent decades to improve the low-frequency isolation performance without increasing the static displacement. This work is devoted to the concrete realization of a QZS isolator by utilizing transverse groove springs. Firstly, the QZS isolator is theoretically analyzed and some dynamical indices are analytically calculated. Then, the transverse groove springs are designed and the isolator prototype is assembled; the QZS feature of the prototype is basically fulfilled. Finally, the experiments are conducted by means of an electrodynamic shaker which generates sinusoidal base excitation for the isolator prototype; the experimental results clearly show the good isolation performance of the QZS isolator and meanwhile reflect some practical factors that should be noticed in actual applications.
TL;DR: In this article, three-dimensional fully coupled thermo-mechanical models of RFSSW joints between Alclad 7075-T6 aluminium alloy sheets have been built in the finite-element-based program Simufact Forming.
Abstract: Refill friction stir spot welding (RFSSW) is a solid state joining technology that has the potential to replace processes such as the open-air fusion bonding technique and rivet technology in aerospace applications. Selection of proper RFSSW parameters is a crucial task which is important to ensure the mechanical strength of the joint. The aim of this paper is to undertake numerical modelling of the RFSSW process to understand the physics of the welding process, which involves large deformations, complex contact conditions and steep temperature gradients. Three-dimensional fully coupled thermo-mechanical models of RFSSW joints between Alclad 7075-T6 aluminium alloy sheets have been built in the finite-element-based program Simufact Forming. The simulation results included the temperature distribution and the stress and strain distributions in the overlap joint. The results of numerical computations have been compared with experimental ones. The numerical model was able to predict the mechanics of material flow during the joining of sheets of Alclad aluminium alloys using RFSSW. The predictions of the temperature gradient in the weld zone were in good agreement with the temperature measured experimentally. The numerical models that have been built are capable of simulating RFSSW to reduce the number of experiments required to set optimal welding parameters.
TL;DR: In this article, the microstructure analysis with electron backscatter diffraction (EBSD), measurements of microhardness HV over cross-section, and tension test for determination of mechanical properties were carried out for these rods.
Abstract: The features of microstructure formation and properties of commercial pure aluminum alloy (Al 99.5%) obtained by radial-shear rolling (RSR) method at the different heating temperatures of 25, 200, 250, 300 and 350 °C were examined. In this paper, the rods with diameter of 14 mm were obtained from initial billet with diameter of 60 mm in five passes. The microstructure analysis with electron backscatter diffraction (EBSD), measurements of microhardness HV over cross-section, and tension test for determination of mechanical properties were carried out for these rods. The FEM simulation of RSR process and calculation of Zener–Hollomon parameter (Z) were carried out with Software QFORM. The obtained rods have the gradient microstructure typical of RSR characterized by surface layer with ultrafine grain structure (UFG) and grain size from 0.3 to 5 µm. In the central part of rod, the fiber deformed structure with minimal fraction of recrystallized grains (< 5%) is formed. This combination is optimal for simultaneous achievement of high strength (UTS ~ 107–110 MPa; YS ~ 100–109 MPa; ~ 35–40 HV) and ductility (El ~ 15–30%). The most intensive growth of plastic properties is observed at rolling temperatures close to the temperature of the onset of recrystallization, it is associated with additional deformational heating of surface layers and the formation of partially recrystallized structure. The obtained distribution dependences of average size of dynamic recrystallized grain on Zener–Hollomon parameter showed that the decrease in parameter Z leads to the increase in size of recrystallized grain for RSR process.
TL;DR: In this article, the long-term impact on creep, drying shrinkage, and permeation characteristics of an innovative concrete produced with manufactured geopolymer coarse aggregate (GPA) has been investigated and compared with quarried Basalt aggregate concrete.
Abstract: The long-term impact on creep, drying shrinkage, and permeation characteristics of an innovative concrete produced with manufactured geopolymer coarse aggregate (GPA) has been investigated and compared with quarried Basalt aggregate concrete. Microstructure and pore-structure development up to 1 year were examined through scanning electron microscopy, nanoindentation, and X-ray computed tomography. Compressive strength and elastic modulus of GPA concrete varied from 34.6 to 50.8 and 18.5 to 20.5 GPa, respectively, between 28 and 365 days. The 1-year creep strain of GPA concrete was 747 microstrain while the calculated creep coefficient was 0.97, which is significantly lower than the creep coefficient predicted by AS 3600 and CEB-FIP models. Moreover, the 365-day drying shrinkage is 570 microstrain, which is also lower than the maximum permissible limit specified by AS3600. The GPA concrete displayed high water absorption, but lower air and water permeability compared to Basalt aggregate concrete. This is attributed to a porous surface layer with large number of capillaries increasing the water absorption of GPA concrete through capillary suction. The discontinuity in the pore network coupled with a condensed interfacial transition zone formed in GPA concrete could be the reason for lower permeability. Overall, the long-term performance of the GPA demonstrates a potential as a lightweight coarse aggregate for concrete, with the added advantage of reducing the environmental impact utilizing fly ash from coal-fired power generation.
TL;DR: In this article, cork grains of very small size (0.5-1.0mm) are added to two different shear thickening suspensions, one of them a fully natural water and cornstarch, and the other based on fumed silica and polyethylene glycol.
Abstract: Shear thickening fluid (STF) is a very interesting and promising material in several application fields where a different mechanical is demanded based on loading rates, like body armor and vibration insulators. Cork is a natural cellular material by excellence, filled with well-known beneficial effects in terms of insulation and also interesting crashworthiness properties. In this work, cork grains of very small size (0.5–1.0 mm) are added to two different shear thickening suspensions, one of them a fully natural water and cornstarch, and the other based on fumed silica and polyethylene glycol. The rheology of these eco-friendly suspensions was investigated and the influences of including cork grains were discussed. In addition, microscopic analyses were carried out to observe the deformations at each component during the shear thickening phenomenon. Cork grains reduce the load-carrying capacity in the suspensions due to the deformable characteristics of cork. For this reason, shear thickening properties are suppressed in the mixtures. Despite this, it is possible to state that viscosity increase in the mixtures leads to strong particle contacts, and thereby resulting in particle deformations in the main constituent powder as well as in the cork additives due to their softer structures.
TL;DR: In this paper, the influence of corroded steel bars on seismic performance of reinforced concrete (RC) columns was investigated and fabricated, which were composed of one uncorroded RC column, three RC columns with longitudinal reinforcement corrosion and four stirrup-corroded columns.
Abstract: To investigate the influence of corroded steel bars on seismic performance of reinforced concrete (RC) columns, eight full-scale RC columns were designed and fabricated, which were composed of one uncorroded RC column, three RC columns with longitudinal reinforcement corrosion and four stirrup-corroded RC columns. The electrochemical test was conducted to accelerate the corrosion of steel bars in RC columns, and the low-cyclic repeated loading tests on RC columns with corrosion-damaged steel bars were carried out. The seismic behavior indicators, including the hysteretic curves, skeleton curves, displacement ductility coefficient, stiffness degradation curves and energy dissipation capacity of corroded RC columns and uncorroded columns, were compared and discussed. The experimental results show that with the increase in steel bars corrosion degree, the pinch phenomenon of the hysteretic curve gradually increases, and the energy dissipation capacity, stiffness and plastic deformation capacity of specimen reduce significantly. The ductility and energy dissipation coefficient decreased by 20% and 36%, respectively, when the stirrups corrosion ratio of specimen reaches 15.2%, and a shear failure surface was formed in the plastic hinge zone at the foot of the columns, which leads to the change of failure mode from ductile bending failure to shear failure with poor ductility under the ultimate load for corroded columns. The influence of stirrup corrosion on the failure mode of specimens is remarkable, but the effect of longitudinal reinforcement corrosion is negligible for specimens with the corrosion ratio within 14.7%. The adverse effects caused by over 15.2% stirrup corrosion should be considered in seismic design of structures in seismic zone.