Showing papers in "Procedia structural integrity in 2020"

Effect of manufacturing parameters on tensile properties of FDM printed specimens

Abstract: Nowadays, one of the most studied technologies for obtaining different parts is Additive Manufacturing (AM) Whether it is about plastic or metal materials, AM is used because very complex parts can be obtained, without further technological operations From all AM technologies, Fused Deposition Modeling (FDM) is the most used all over the world, due to its cost-effective way of printing FDM is based on the extrusion of a wire, through which a piece is formed by successively depositing layer-by-layer of molten material This paper experimentally investigates the tensile properties of 3D printed specimens obtained through FDM printing The influence of spatial printing direction (0°, 45°, 90°) and size effect (different thickness) on main mechanical properties was investigated Polylactic acid (PLA) dog bone specimens were adopted for all tensile tests Experimental tests were carried out at room temperature, according to ISO 527-1 Standard It was observed that the spatial orientation has less influence on the Young modulus and higher influence on the tensile strength Furthermore, increasing the number of layers leads to decreasing of both the Young modulus and tensile strength

3D printed continuous carbon fiber reinforced PLA composites: A short review

Abstract: Additive manufacturing is a flexible processing technique that can be applied to polymers, metals, ceramics and other materials. Fused Deposition Modelling (FDM) is one of the available additive manufacturing techniques that use thermoplastic polymers to print components/structures. Although there are many materials that can be used as filaments in this technique, PLA is one of the most widely used, not only for its characteristics, but also for society’s environmental awareness. Depending on the desired characteristics of 3D printed models, PLA can be reinforced with fillers. Therefore, this short review paper aims to summarize all studies involving continuous carbon fibre reinforced PLA composites.

Effects of raster layup and printing speed on strength of 3D-printed structural components

Abstract: Three-dimensional (3D) printing, formally known as Additive Manufacturing (AM) has been significantly developed and widely used in recent years. Although this manufacturing process was utilized for prototyping, currently it has been used in rapid manufacturing of final products. Therefore, study behavior of 3D-printed parts is a crucial issue. In this context, current study presents the influence of two printing parameters on strength of 3D-printed components. In detail, Polylactic Acid (PLA) material was used in the fabrication of specimens by Fused Deposition Modeling (FDM) process. In this study, two printing parameters (a) raster layup and (b) printing speed were changed in the fabrication of 3D-printed parts. A series of experimental tests were conducted to show effects of the mentioned printing parameters on stiffness and strength of the examined components. The obtained results showed stiffness and strength depend on raster angle. In detail, highest and lowest strength have been achieved for 0° and 90° raster angles, respectively. The documented results can be used for future research studies and next computational models.

The use of Biochar to reduce the carbon footprint of cement-based materials

Abstract: The organic waste management is a most current topic, because its processing and degradation it is responsible for emissions of methane and other greenhouse gases, leading to serious environmental problems Limited oxygen thermochemical processes, such as pyrolysis or gasification, have demonstrated the energy recovery potential of the treated biomass and its environmental benefits However, the solid part of the process -Biochar- it is considered as a waste, as only its coarse ash can be used as soil improvers Nevertheless, several researchers have explored its potential application as green filler in order to reduce the carbon footprint both of cement production and cement-based construction materials In this work, Biochar microparticles were used both as a filler inside the cement paste and mortar composites and as a substitute for the cement powder inside the mixes Based on previous work, this investigation has a twofold objective: to understand the full influence of the use of an optimized percentage of Biochar (2% with respect to the weight of the cement) either as a filler in the mixture or as a substitute for cement, while guaranteeing an improvement in the strength without losing ductility The results showed that 2 wt% of Biochar’s particles are sufficient to increase the strength and toughness of the cement and mortar composites and, in place of the cement in the mixture, can maintain the mechanical properties equal to those of the reference samples

Mechanical characterization of different biochar-based cement composites

Abstract: The attention on the use of raw materials, the energy consumption as well as carbon dioxide production of cement factories are boosting the experimentation on innovative and sustainable materials in concrete technology. In recent years, biochar has become an emblematic material with a thousand facets. Mainly investigated up to now as amending in the agricultural field, biochar can be explored as a building material due to its innumerable properties. Indeed, several applications have been studied to use it as a filler to modify the nanogranular nature of the cement matrix, or as a substitute for clinker, aggregates and clay, reducing the carbon footprint and the emissions of greenhouse gases linked to the production processes of cementitious materials. In this paper, nano/micro-particles of biochar, the solid by-product from the gasification process of biomass derived from wood waste, has been used in different cement composites aiming at determining the optimal percentage of addition while trying to guarantee an improvement of mechanical properties. The results showed that an optimized percentage of biochar nano/micro-particles can increase the strength and toughness of the composites.

Free Vibration Analysis of Interfacial Debonded Sandwich of Ferry Ro-Ro’s Stern Ramp Door

Abstract: The dynamic characteristic of interfacial debonded Ferry Ro-Ro’s stern ramp/door is studied by using finite element software ABAQUS. The effect of debonding on vibration responses of damaged stern ramp/doors is assessed by comparing numerical parameters of natural frequency shifts between intact and damaged models. Parametric studies over a wide range of debonding shapes to explore the influence of this parameter on the overall dynamic behavior of the models are investigated. Boundary conditions describing the loading conditions of the ship are evaluated. Four different debonding shapes with a similar debonding ratio, such as circular, square, through-the-length, and through-the-width, are investigated. To evaluate the effect of modeling techniques, both debonding shapes with and without spring contact element models are examined. Consequently, natural frequencies shift is being determined as functions of these parameters that enable to conclude the influence of debonding. The result has been shown that the debonding defect reduced the natural frequencies, especially in the square and circular debonding shapes. There is no significant frequency shift in the through-the-length, and through-the-width debonding modeling. Neglecting of contact leads to incorrect results, which significantly overestimate the value of natural frequency, so the spring contact modeling is recommended. The higher natural frequencies are found to be more sensitive to the presence of debonding problems. Using natural frequency shifts directly resulting from both intact and debonded models, the diagnostic can be performed.

The effect of crack insertion for FDM printed PLA materials on Mode I and Mode II fracture toughness

Abstract: The paper presents mode I and II fracture toughness results for polylactic acid material obtained via fused deposition modeling. The tests were performed using Single Edge Notch Bend specimens loaded in four point bending: symmetric for mode I, asymmetric for mode II, respectively. The notch was inserted by 3D printing, and by milling, respectively. Fracture toughness values measured for the specimens with 3D printed notch resulted to be higher than those obtained by milling. The effect of notch insertion is more evident in mode I while it is less important for mode II.

Comparative analysis of printing parameters effect on mechanical properties of natural PLA and advanced PLA-X material

Abstract: FDM is a commercially widespread 3D printing technology which uses thermoplastic materials for building prototypes and functional parts. Most used materials in this technology are PLA (PolyLactic Acid) and ABS (Acrylonitrile Butadiene Styrene) materials which contain dissimilar mechanical properties and printing abilities. PLA is considered as a good material for prototypes and parts that acquire higher dimensional accuracy, and is considered as a material that is easier to print than ABS. Advantages of ABS material, compared to standard PLA are better mechanical properties, sufficiently higher printing speeds and higher heat resistivity. Deficiency of ABS over PLA is shrinking of ABS material after 3D printing-resulting in poor dimensional accuracy or failure during printing. A newly available material PLA-X (‘’mcPP”, Mitsubishi Chemical, Japan) houses advantages of both mentioned materials and may lead to wider commercial and industrial use. Different printing parameters of the same material may lead to different mechanical properties of the finished part. The aim of this paper is to compare how different printing parameters effect on mechanical properties of standard PLA and PLA-X -which is a material that has similar dimensional accuracy of finished parts as PLA and possesses higher mechanical properties like ABS. Samples of PLA and PLA-X where printed in five different printing regimes, varying layer height, number of outline perimeters, infill density and sample humidity, with five samples each (according to ISO 527-2 international standard) and used for mechanical testing on standard tensile testing machine.

Modeling elastic properties of unidirectional composite materials using Ansys Material Designer

Abstract: Advanced reinforced composites are leading materials used in high tech industries (automotive, aerospace, naval, etc.) in recent years. Before manufacturing any structure made by composite materials, it is crucial to analyze their elastic properties by analytical means or computational homogenization to reduce the overall manufacturing cost and time for faster production. In this current research paper, Ansys Material Designer is adopted to estimate the elastic properties of unidirectional composite materials and compare them with available analytical, finite element and experimental results. In general, it yields results with excellent accuracy compared to experimental data for all RVE shapes (square, diamond and hexagonal). However, accuracy loss is found for in-plane shear modulus (G12) when the fiber volume fraction is more than 0.6.

Nano CaCO3 particles in cement mortars towards developing a circular economy in the cement industry

Abstract: This paper calls into question the effects of incorporating nano calcium carbonate (CaCO3) particles in cement mortars, as they are interesting additive materials already successfully tested as cement nanofiller. These nanoparticles could potentially be prepared through the carbonation route using CO2 from combustion gases from the cement industry. This could enable a circular-economy approach for carbon capture and its re-use within the cement industry, in a sustainable and synergistic manner. In this study, part of the cement content was substituted with commercial nano CaCO3 particles to investigate their effects on the flexural and compressive strength of the resulting cement mortars, after curing for 7 and 28 days. Decreasing the cement content could lead to a reduction in the carbon footprint of cement, which is responsible for approximately 8% of global carbon dioxide emissions. Preliminary results using synthesized CaCO3 particles as nanofillers showed that, after 7 days of curing, mechanical properties of cement mortars improved. This indicates that hydration reaction was accelerated since CaCO3 acts as seeding for this reaction. By contrast, after 28 days of curing, no major improvement was observed. A higher content of calcium carbonate nanoparticles may have reduced the filler effect of these particles due to aggregation phenomena. In the present work, the effects of commercial nano CaCO3 particles on cement hydration were investigated. Mechanical tests showed promising results both after 7 and 28 days of curing. This could lead to the reduction of the carbon footprint of cement manufacturing and produce increasingly better performing building materials. Thus, the development of a circular economy in the cement industry could be achieved.

Flexural Strengthening of Reinforced Concrete Beams with Externally Bonded Hybrid Systems

Abstract: Carbon fiber reinforced polymers (FRP) have been used widely as Externally Bonded Reinforcing (EBR) materials for strengthening and retrofitting of RC structural members, both in flexure and shear. The use of high strength Galvanized Steel Mesh (GSM) strengthening material has recently gained wide acceptance as well. Both CFRP and GSM have many advantages and some shortcomings. One of their major shortcoming is the lack of ductility. Recently developed Aluminum Alloys (AA) has high ductility and some desirable features that may overcome some of the shortcomings of GSM and CFRP laminates. The major aim of this research is to develop a hybrid ductile strengthening system by combining AA plates with GSM and CFRP laminates to strengthen RC beams in flexure. An experimental program that includes tensile test of six coupon specimens and five flexure tests of beam specimens were conducted. The test results showed the effect of hybrid combination on both strength and ductility of the tested beams and that the newly proposed hybrid systems are promising in improving the flexural behaviour in terms of strength and ductility. The tested hybrid coupons of AA with high density steel mesh (SMH) and AA with CFRP showed an increase in the strain capacity by 6.52 and 4.55 times, respectively compared to that of GSM and CFRP alone. The flexural capacity of the beams strengthened with hybrid laminate increased by around 28% over the control beam, while the beam strengthened with hybrid GSM and AA (SMH+AA) laminate showed an ultimate deflection equivalent to 98.5% of the un-strengthened control beam. The failure modes of the tested beams included debonding and delamination and they were influenced by the type of hybrid system used.

Slow-growth damage tolerance for fatigue after impact in FRP composites: Why current research won’t get us there

Abstract: Impact damage in CFRP structures is currently managed using the ‘no-growth’ concept, meaning that damage is not allowed to grow under fatigue loading. This requires that stresses in the material are kept below the fatigue limit, imposing a significant weight penalty. A ‘slow-growth’ concept would allow more efficient structural designs, but several knowledge gaps need to be addressed before this is possible. These gaps exist in three main areas: (1) damage characterisation, (2) fatigue driven delamination growth after impact, and (3) final failure of impacted laminates. The paper highlights open questions and the shortcomings of current research in addressing them, and suggests avenues for future research.

Evaluation of fatigue properties of 3D-printed Polyamide-12 by means of energy approach during tensile tests

Abstract: Rapid prototyping and Additive Manufacturing are experiencing a continuous and rapid growth in different industrial fields, ranging from automotive to biomedical applications. They allow the creation of a wide range of devices in a short time with several materials, such as polymers and metals. On the other hand, the manufacturing process considerably affects the performance of the obtained 3D-printed materials and different laboratory tests are required in order to assess the mechanical properties, especially the fatigue behavior, of these materials. The present work is the result of the collaboration between the Engineering Department of the University of Messina and the rapid-prototyping company Skorpion Engineering. The aim of this work is to apply, for the first time on 3D-printed materials, the Static Thermographic Method for the fatigue assessment of Polyamide-12.

Design for NVH: topology optimization of an engine bracket support

Abstract: Noise Vibration and Harshness (NVH) issues are proven to be the main drivers for customer dissatisfaction in the latest years. This work relies on the framework of Design For X (DFX), specifically, Design for NVH. Main goal of this work was to perform a Topology Optimization (TO) of an engine bracket based on its vibrational behavior, in order to reduce the vibrations transmitted from the engine to the chassis and, consequently, improving the comfort for passengers. In particular, the target function was defined with the aim of increasing the first natural frequency of the bracket, whereas the bracket mass reduction was considered as a constraint function for the TO process. The vibrational characterization of the bracket was based on Frequency Response Function (FRF) analyses which, conducted via FEM (Finite Element Method), allowed to identify the resonant frequencies of the different bracket configurations built up during the TO. The FEM models included the cylinder head, with the related engine bracket support under optimization; the latter is connected to the bracket on which the simulation load was applied. The TO turned out to be effective in lowering the mass of engine bracket support of nearly 20% and, at the same time, increasing the first natural frequency of nearly 10%, this latter result was sufficient to guarantee an improvement of the comfort for passengers.

Recent Developments on Underwater Welding of Metallic Material

Abstract: Underwater welding is the process of connecting two similar or different metals which are carried out underwater. This process is applied in various construction of engineering materials both on land and underwater environments such as in ship construction, oil and gas mining in the middle of the sea and nuclear power plants. Material construction greatly influences the method suitable for the welding process. It will affect the evolution of the microstructure and mechanical properties of the material. So, it will affect the results of the welded joint.

Determination of Fatigue Limit by Static Thermographic Method and Classic Thermographic Method on Notched Specimens

Abstract: The aim of the present work is to investigate the possibility to evaluate the fatigue limit of such a component through the so-called Static Thermographic Method (STM) This new approach has been proposed in 2013 by Risitano and Risitano to determinate the fatigue limit of metallic materials through static tensile tests Investigating the trend of the surface temperature of the material during static tensile test, the method proposes to correlate the first deviation from linearity of the surface temperature to a damage limit that has been proven to have relation with the fatigue limit Static tensile tests at different stress rate have been carried out on V-notched specimens Stepwise fatigue tests have been carried out in order to apply the classic Thermographic Method that has been hugely validated to determinate the fatigue limit of metallic components Static tests at different stress rate showed that the method is dependent on this parameter; anyway, this dependence does not affect the results achieved in terms of fatigue limit The experimental results showed a good agreement with the energetic methods considered in the present work

A note on computing the growth of small cracks in AM Ti-6Al-4V

Abstract: The certification requirements for additively manufactured (AM) replacement parts requires the ability to predict the growth of small sub mm cracks. To this end, it is shown that the Hartman-Schijve crack growth equation proposed in a prior paper for the growth of small cracks in AM Ti-6Al-4V manufactured specimens also accurately predicts the growth of small cracks in Laser Beam Powder Bed Fusion (LB-PBF) manufactured Ti-6Al-4V specimens. The specimens studied are built with two different LB-PBF machines with different processing parameters. Particular attention is given to the growth of crack from initial sizes that are of the same order of magnitude as the minimum equivalent initial damage size (EIDS) in the US Air Force (USAF) approach to the certification of an AM replacement part.

Investigation of Industrial and Agro Wastes for Aluminum Matrix Composite Reinforcement

Abstract: Sustainable development of materials, environmentally friendly, and low-cost production is the background of this paper. The researchers focus on developing lightweight metal matrix composite materials with various reinforcements from chemical processes such as Al2O3, SiC, and graphite. These additions resulted improve in mechanical, physical, thermal, and corrosion properties of the materials. This paper offers the potential of alternative reinforcing materials that are inexpensive, easily accessible, and physical and mechanical properties equal to conventional particulates. Industrial and agricultural wastes that rich in oxide material can be used as an alternative material in metal matrix composite. Based on a review of the literature, various debris such as fly ash, bottom ash, rice husk ash, bean pod ash has been used as reinforcement in metal matrix composites. The literature states that the addition of particulates from industrial and agricultural waste improved the mechanical properties of composite materials.

A detailed micro-model for brick masonry structures based on a diffuse cohesive-frictional interface fracture approach

Abstract: In the past decades, the mechanical behavior of brick masonry material has been largely investigated using different modeling strategies, ranging from purely microscopic to purely macroscopic ones. The so-called simplified micro-modeling approaches, in which the behavior of mortar joints and brick/mortar interfaces is lumped in discontinuous elements, are commonly judged as very effective for accurately representing the interaction between the masonry constituents with an acceptable computational burden. However, they completely disregard the competition between brick/mortar decohesion and mortar cracking, whose role is not negligible, especially in presence of sufficiently thick joints and/or high-strength mortars. In this work, a detailed micro-modeling approach is proposed for the nonlinear analysis of brickworks subjected to in-plane loads. Such an approach allows failure to occur at the brick/mortar interface level and/or inside the mortar layer, while keeping the discrete nature of fracture phenomena. For this purpose, a novel diffuse cohesive-frictional interface approach for joints is presented, able to simulate multiple micro-crack onset and propagation along a-priori unknown paths. Suitable comparisons with a simplified micro-model are provided to validate the proposed approach. Moreover, a good agreement with the experimental outcomes is found, thereby assessing the reliability of the present fracture-based detailed micro-model in the numerical prediction of masonry strength under complex loading conditions.

Shear strengthening of reinforced concrete T-beams using CFRP laminates anchored with bent CFRP splay anchors

Abstract: Strengthening of reinforced concrete (RC) structures via external bonded fiber-reinforced polymer (EB-FRP) systems has been widely documented and used. This form of retrofitting has proven to be effective in enhancing flexural and shear capacity of RC beams. However, it is limited due to premature debonding of the FRP laminates prior to utilizing the laminates strength, and typically results in brittle member failure. To overcome this issue, studies have shown that proper anchorage systems mitigate debonding and enables the achievement of higher strengthening levels. Out of the many anchorage systems researched, FRP splay anchors have proven to be effective in enhancing member’s capacity by delaying the laminates debonding. However, the literature is lacking adequate information on the effect of splay anchors on the performance externally strengthened RC beams in shear. Accordingly, five shear deficient RC T-beams specimens were cast and strengthened with CFRP U-wrapped laminates and anchored with CFRP anchors. The parameter investigated in this study is the anchor dowel diameter. Three dowel diameters were tested: 12 mm, 14 mm, and 16 mm. The performance of the anchored U-wrapped specimens in terms of failure modes, load-deflection responses, shear strength, strain in CFRP laminates, and ductility is compared to that of unstrengthened and unanchored strengthened control specimens. Test results showed that CFRP anchors delayed debonding of the U-wraps, improved the shear strength of unanchored U-wraps, and significantly enhanced the ductility of the beam specimens. In addition, it was concluded that anchoring CFRP laminates with CFRP anchors highly utilized the strain attained in CFRP laminates. No clear trend was observed between anchor diameter and ultimate load-carrying capacity of the specimens. Based on the results of this study, anchor dowel diameter of 14 mm was found optimum for an anchor embedment depth of 85 mm.

IoT sensors for modern structural health monitoring. A new frontier

Abstract: The problem of determining the structural safety level of buildings and civil engineering infrastructures (CEIs) is raising growing concern worldwide. Most of the reinforced concrete constructions have a design life not greater than 100 years, and today it is necessary to face the problem of assessing their level of safety and structural integrity. Such problem is even more pressing when a construction is subjected to extreme environmental conditions. The long-term goal of this study is the realization of wireless lowcost devices, and a data management software, for the structural health monitoring of buildings and CEIs, with remotely controlled sensors embedded in, or installed on, the structural elements, to measure stresses together with accelerations. Once equipped with such system, each construction can become part of the Internet of Things, permitting users and authorities to be alerted in case structural safety is diminished or compromised. A crucial aspect is the unaltered preservation of measurement data over time, which cannot just rely on third parties, and for which it is necessary the exploitation of suitable data-protection technologies. This study have been carried out by experimental testing and validation, both in lab and on site, of the monitoring devices designed and realized. Results show that it is possible to realize low-cost monitoring systems, and related installation techniques, for integration in every new or existing buildings and CEIs

Production issues in the manufacturing of TiAl turbine blades by investment casting

Abstract: γ -TiAl based intermetallic alloys have attracted broad attention as a potential candidate for high-temperature structural applications. A careful selection of their composition and microstructure allows to obtain an interesting combination of oxidation resistance, creep resistance and high temperature strength for specific applications. Over the years, several complex manufacturing methods have been used for producing TiAl parts. In this work TiAl blades have been produced by means of investment casting. The work analyses the different production steps: design of a blade prototype, production of an ABS model by additive manufacturing that is used to make the wax model, preparation of the ceramic mold and centrifugal casting of the component. All the production issues related to TiAl alloy investment casting have been analyzed with the aim of setting up a tailored process able to produce sound components.

Effect of Reinforcement Material on Properties of Manufactured Aluminum Matrix Composite Using Stir Casting Route

Abstract: Composite is a lightweight material that used and developed in various industries. The use of aluminum matrix composites as structural and automotive materials has increased in recent years. One of the obstacles in the development of aluminum matrix composites is high-cost production, especially raw material for reinforcing particles. One innovation is the use of natural materials and waste as reinforcement in aluminum matrix composites. Sea sand is one of the natural materials containing ceramic or oxide compounds so that it has the potential to be used as reinforcement in aluminum matrix composites. This paper compares the physical and mechanical properties of aluminum composite production using sea sand particles and composites with commonly used ceramic particle reinforcement, such as alumina and SiC. Calculation of density and porosity shows that Al6061/sea sand composites have higher density and lower porosity compared to Al6061/Al2O3 and Al6061/SiC composites. The hardness of Al6061/sea sand composite is higher compared to Al6061/Al2O3 and Al6061/SiC composites.

Finite Element Analysis (FEA) on Autonomous Unmanned Surface Vehicle Feeder Boat subjected to Static Loads

Abstract: Unmanned Surface Vehicle (USV) has many roles in various maritime fields. In Indonesia, many fish farmers still do the process of feeding fish manually using human labor. For fish farmers who have a more extensive pond can only sow fish feed on the edge of the pond, so that fish feed cannot be evenly distributed to the middle of the pond. This autonomous surface vehicle feeder boat is made as a solution to the problem of fish farmers who have a large pond size in fish feed distribution more evenly. Fish feeding is done automatically by an autonomous surface vehicle feeder boat with a fish feed capacity of up to 8 kg. The autonomous surface vehicle feeder boat is equipped with an ultrasonic sensor that is connected to a microcontroller to move the boat steering wheel to turn when a collision occurs with a pool boundary. The autonomous surface vehicle feeder boat has two control modules, which are moving automatically or manually using a remote control. Users can change the settings of this module from the remote control as needed. The hull used is the catamaran hull type. Catamaran hull was chosen because it has a good level of stability. Hull construction on this boat must have the strength that can sustain all the burden on the boat. Therefore, in this paper, the hull design of the boat tested with balsa wood material uses the Finite Element Analysis (FEA) method to determine the strength of stress, strain, and displacement that may occur using 3D mechanical design. Static loading is chosen in the hull design test method. This test analysis is used to determine whether the design with the specified material can be made.

Fracture and Damage to the Material accounting for Transportation Crash and Accident

Abstract: In this paper, reviews of several fractures and damage to materials in their use are presented. As happened in the coal train axle and the gas pipelines are corrosion and can cause fracture and damage. Prevention and lessons that can be drawn from several events are positive things to avoid similar incidents in the future. Damage to the material also can occur one of them due to the influence of nature like floods and earthquakes. This paper also reviews crashes in transportation, one of which is due to a lack of attention among motor vehicle drivers who contribute to almost one in three fatal traffic accidents between 2011 and 2015 in Norway. Hence, the finite element method done to estimate the event of a crash between transportation to improve passenger safety as consideration is the location of the center of gravity of the vehicle and the safety of the passenger compartment.

From TLS data to FE model: a workflow for studying the dynamic behavior of the Pulpit by Giovanni Pisano in Pistoia (Italy)

Abstract: This paper discusses the first results of an ongoing two-year research activity aimed to identify the actual dynamic behavior of the Pulpit of Giovanni Pisano in Pistoia in order to design a long-term structural health monitoring system. First steps of the research have foreseen a Photogrammetric and Terrestrial Laser Scanner (TLS) survey of the structure in order to build a refined digital three-dimensional geometric model of the Pulpit to be employed for both documentation and structural assessment. The paper reports the main outcomes of the TLS survey together with the procedure employed to obtain a reliable finite element model of the Pulpit. An original workflow for direct transfer of high accuracy TLS-based three-dimensional model to a finite element model is proposed and discussed.

Nonlinear analysis of microscopic instabilities in fiber-reinforced composite materials

Abstract: Failure induced by fiber microbuckling is a frequent failure mode in continuous fiber-reinforced composite materials subjected to compression along the fibers direction. This failure mechanism may lead to a notable decrease of the compressive strength of composite materials since may also induce the initiation and propagation of cracks at the micro-structural level. A detailed microscopic continuum analysis with an appropriate representation of different sources of nonlinearities is usually required to capture the effects of different microscopic failure modes (instability, fracture damage, for instance), at the expense of a very large computational effort. In order to avoid a direct modeling of all microstructural details of the composite solid, micromechanically based multiscale techniques can be adopted in coupling with first order homogenization schemes. To this end a semiconcurrent two-scale approach is proposed in which the macroscopic constitutive law is evaluated resolving a micromechanical BVP in each macroelement of the homogenized domain; the microscopic model adopts a full finite deformation continuum formulation to study the interaction between local fiber buckling and matrix or fiber/matrix interface microcracks in presence of unilateral self-contact between crack surfaces. Numerical results are obtained to provide accurate predictions of the critical load level associated to microscopic instabilities in 2D fiber-reinforced composite solids.

On the accuracy of UAV photogrammetric survey for the evaluation of historic masonry structural damages

Abstract: Photogrammetric surveys via Unmanned Aerial Vehicles are nowadays a valuable tool for historic masonry structures inspection, surveillance, mapping and 3D modeling issues. When structural damage mapping and structural assessment are of interest obtaining accurate and reliable geometric models is a crucial issue. Therefore, the flight plan, the georeferencing and the data processing steps need to be properly designed. In this paper, a procedure for the photogrammetric survey via Unmanned Aerial Vehicles of a masonry structures is used in order to obtain effective visual inspections and a 3D model of a historic masonry arch bridge located along the ancient Via Amerina (Todi, Perugia, Italy). The photogrammetric survey provides a detailed representation of the actual geometry, including lack of volumes and significant cracks along the vault and the spandrel walls, outlining a severe damage state affecting all the structure. Finally, a Total Station and a Laser Scanner were used to compare the results obtained by photogrammetry, highlighting the advantages, the limits and the weaknesses offered by their use.

Mechanical behavior and crack propagation of ABS 3D printed specimens

Abstract: The present paper analyzes manufacturing density effect on the mechanical properties of three-dimensional (3D) printed ABS specimens. Indeed, the optimum density of the printed specimens is investigated to reach the extruded specimens’ characteristics. Then, the mechanical properties such as the tensile strength, the Young’s modulus, the ultimate tensile and yield strength, the ductility and fracture toughness are identified and compared. Furthermore, we study crosshead speed effect on printed samples with an infill rate of 100% towards crack propagation. Subsequently, the stress intensity factor is determined. The results indicate a considerable effect of the density and the filling rate on tensile properties and on the rupture propagation.