Showing papers on "Tensile testing published in 2020"

Microstructural and tribological characteristics of AA6351/Si3N4 composites manufactured by stir casting

Abstract: In the current research study, AA6351 (Al-Si-Mg) is employed as matrix material and silicon nitride (Si3N4) particles as reinforcement material to manufacture the aluminum composites (AMCs). AA6351 matrix composites incorporated with several weight fractions of Si3N4 (0, 1, 2 and 3 wt.%) were synthesized via stir casting technique. The obtained composites were characterized through a scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS). EDS and XRD spectrums demonstrate the presence of Si3N4 reinforcement contents in the manufactured AMCs. The SEM analysis exhibits the even dissemination of Si3N4 particles in the Al alloy. The mechanical properties of the composites are examined by conducting several kinds of tests like compression test, impact test, tensile test and hardness test to understand the relationship between the weight percentages of reinforcement on the mechanical characteristics of the manufactured AMCs. The un-lubricant tribological characteristics of the proposed AMCs were assessed utilizing pin on disk tribometer. The hardness, compression and tensile strength of the AMCs were augmented concerning the mass proportion of reinforcement content. Finally, the wear test result reveals that the addition of nano-sized Si3N4 reinforcement contents up to a mass proportion of 3% downgrades the wear rate.

Ultrahigh high-strain-rate superplasticity in a nanostructured high-entropy alloy

Abstract: Superplasticity describes a material’s ability to sustain large plastic deformation in the form of a tensile elongation to over 400% of its original length, but is generally observed only at a low strain rate (~10−4 s−1), which results in long processing times that are economically undesirable for mass production. Superplasticity at high strain rates in excess of 10−2 s−1, required for viable industry-scale application, has usually only been achieved in low-strength aluminium and magnesium alloys. Here, we present a superplastic elongation to 2000% of the original length at a high strain rate of 5 × 10−2 s−1 in an Al9(CoCrFeMnNi)91 (at%) high-entropy alloy nanostructured using high-pressure torsion. The high-pressure torsion induced grain refinement in the multi-phase alloy combined with limited grain growth during hot plastic deformation enables high strain rate superplasticity through grain boundary sliding accommodated by dislocation activity. Superplasticity at high strain rates is challenging to achieve in high strength materials. Here, the authors show superplastic elongation in excess of 2000% in a high entropy alloy nanostructured by high-pressure torsion.

Effects of the addition of silicon to 7075 aluminum alloy on microstructure, mechanical properties, and selective laser melting processability

Abstract: Aluminum alloys that can be processed using the selective laser melting (SLM) technique have been restricted to cast alloys based on the Al–Si binary system. To increase the selection of materials available for SLM, researches on SLM processability using wrought Al alloys (e.g. 2xxx, 7xxx series) have been conducted. The 7075 Al alloy has excellent mechanical properties among aluminum alloys; however, 7075 alloy has the problem of severe cracking occurring in parts fabricated through the SLM process. Our study demonstrated that additional silicon enables the fabrication of 7075 SLM parts without major defects and that the amount of silicon content changes the favorable processing conditions, morphology of microstructure, and mechanical properties. As the silicon content increased, voids and cracking in SLM samples were suppressed, and volumetric energy density for sufficient densification was reduced. Vickers microhardness and 0.2% proof strength were enhanced with increments of additional silicon content. In contrast, excessive silicon content resulted in brittleness, which appeared as slight ductility measured on tensile testing and breakage of samples during SLM process. These conflicting effects indicated that silicon content must be adjusted depending on the underlying alloy to yield better processability and a balance between strength and ductility. For the 7075 alloy, the optimal silicon content could be concluded to be 5%, being the lowest amount of silicon content needed for the elimination of cracking with enhanced tensile strength and acceptable ductility.

Stress-strain curves of metallic materials and post-necking strain hardening characterization: A Review

Abstract: Fatigue Fract Eng Mater Struct. 2019;1–17. Abstract For metallic materials, standard uniaxial tensile tests with round bar specimens or flat specimens only provide accurate equivalent stress–strain curve before diffuse necking. However, for numerical modelling of problems where very large strains occur, such as plastic forming and ductile damage and fracture, understanding the post‐necking strain hardening behaviour is necessary. Also, welding is a highly complex metallurgical process, and therefore, weldments are susceptible to material discontinuities, flaws, and residual stresses. It becomes even more important to characterize the equivalent stress–strain curve in large strains of each material zone in weldments properly for structural integrity assessment. The aim of this paper is to provide a state‐of‐the‐art review on quasi‐static standard tensile test for stress–strain curves measurement of metallic materials. Meanwhile, methods available in literature for characterization of the equivalent stress–strain curve in the post‐necking regime are introduced. Novel methods with axisymmetric notched round bar specimens for accurately capturing the equivalent stress–strain curve of each material zone in weldment are presented as well. Advantages and limitations of these methods are briefly discussed.

Effect of fiber orientation and fiber loading on the mechanical and thermal properties of sugar palm yarn fiber reinforced unsaturated polyester resin composites

Abstract: Sugar palm [Arenga pinnata (Wurmb.) Merr] fiber reinforced unsaturated polyester resin composites with 0°, 45°, and 90° fiber different orientations were prepared and tested. The composites were characterized for tensile, flexural, impact and compression properties using ASTM D3039, ASTM D790, ASTM D250, and ASTM D3410 standards, respectively. For the thermal characterization, dynamic mechanical analysis (DMA) was conducted to characterize the on storage modulus (E’), loss modulus (E’’) and damping behavior (tan δ) of the composites. The highest mechanical performance of composites was achieved at 0° of fiber orientation composites followed by 45° and 90° fiber orientations. The fiber loading was insignificant for the 90° fiber orientation as the properties were inconsistent. The theoretical value of modulus from the tensile test was calculated using rules of mixture (ROM) and compared with the experimental values for all composites specimens. This research showed that the optimum properties occurred at 30 wt % fiber loading as reflected by the superior tensile and flexural strengths. The optimum properties of compression, impact, storage modulus and better damping properties were achieved at 40 wt % fiber loading.

Additive manufacturing of multiple materials by selective laser melting: Ti-alloy to stainless steel via a Cu-alloy interlayer

Abstract: The ability to combine multiple materials (MM) into a single component to expand its range of functional properties is of tremendous value to the ceaseless optimization of engineering systems. Although fusion and solid-state joining techniques have been typically used to join dissimilar metals, additive manufacturing (AM) has the potential to produce MM parts with a complex spatial distribution of materials and properties that is otherwise unachievable. In this work, the selective laser melting (SLM) process was used to manufacture MM parts which feature steep material transitions from 316L stainless steel (SS) to Ti-6Al-4V (TiA) through an interlayer of HOVADUR® K220 copper–alloy (CuA). The microstructure in both the CuA/SS and TiA/CuA interfaces were examined in detail and the latter was found to be the critical interface as it contained three detrimental phases (i.e. L21 ordered phase, amorphous phase, and Ti2Cu) which limit the mechanical strength of the overall MM part. By making use of the non-homogeneity within the melt pool and limiting the laser energy input, the relatively tougher interfacial α′-Ti phase can be increased at the expense of other brittle phases, forming what is essentially a composite structure at the TiA/CuA interface. During tensile testing, the interfacial α′-Ti phase is capable of deflecting cracks from the relatively brittle TiA/CuA interface towards the ductile CuA interlayer and an overall tensile strength in excess of 500 MPa can be obtained. This method of introducing an interfacial composite structure to improve MM bonding is envisioned to be applicable for the SLM of other metallic combinations as well.

Enhanced strength and ductility of Al-SiC nanocomposites synthesized by accumulative roll bonding

Abstract: This paper present experimental study on improving mechanical properties of Al and Al-xSiC nanocomposites (x = 1, 2 and 4%) synthesized by Accumulative Roll Bonding (ARB) technique. SEM, EDX and XRD analysis was used to characterize the structural changes in the manufactured materials while tensile and microhardness tests were used to characterize their mechanical properties. Homogeneous distribution of SiC nanoparticles was achieved after five ARB cycles. A significant strength improvement was achieved for processed Al and Al-SiC nanocomposites after five ARB cycles due to grain refinement, grain misorientation and SiC strengthening. The grain refinement and grain misorientation contributed the strength improvement by 161% and 46%, respectively, while the addition of 1% SiC nanopartciles contributed by 78% which is increased to 101% for 4% SiC. The ductility is reduced after the zero ARB cycle however it increased with increasing the number of ARB cycles reaching 8.2 and 5.8% for Al and Al-4% SiC nanocomposites, respectively, after 5 ARB cycles. The fracture shape in the ARBed samples is a combination of necking and shearing with a tendency to shearing shape for Al-SiC nanocomposites.

Investigating the Effects of Annealing on the Mechanical Properties of FFF-Printed Thermoplastics

Abstract: Fused filament fabrication (FFF) is a cost-effective additive manufacturing method that makes use of thermoplastics to produce customised products. However, there are several limitations associated with FFF that are adversely affecting its growth including variety of materials, rough surface finish and poor mechanical properties. This has resulted in the development of metal-infused thermoplastics that can provide better properties. Furthermore, FFF-printed parts can be subjected to post-processes to improve their surface finish and mechanical properties. This work takes into consideration two commonly used polymeric materials, i.e., ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid) and compares the results with two metal-infused thermoplastics i.e., copper-enhanced PLA and aluminium-enhanced ASA (acrylonitrile styrene acrylate). The four different materials were subjected to a post-process called annealing to enhance their mechanical properties. The effect of annealing on these four materials was investigated through dimensional analysis, ultrasonic testing, tensile testing, microstructural analysis and hardness testing. The results showed that annealing affects the materials differently. However, a correlation among ultrasonic testing, tensile testing and microstructural analysis was observed for all the materials based on their crystallinity. It was found that the semi-crystalline materials (i.e., PLA and copper enhanced PLA) showed a considerable increase in tensile strength post-annealing. However, the amorphous materials (ABS and aluminium-enhanced ASA) showed a comparatively lower increase in tensile strength, demonstrating that they were less receptive to annealing. These results were supported by higher transmission times and a high percentage of voids in the amorphous materials. The highest hardness values were observed for the ASA material and the lowest for the ABS material. This work provides a good comparison for the metal-infused thermoplastics and their applicability with the commonly used PLA and ABS materials.

Utilization of Random Vector Functional Link integrated with Marine Predators Algorithm for tensile behavior prediction of dissimilar friction stir welded aluminum alloy joints

Abstract: Friction stir welding (FSW) method becomes an effective technique for welding dissimilar alloys such as AA2024 and AA5083 as the conventional fusion welding methods are not very suitable for welding the dissimilar alloysand cause many defects during solidification process. Since the strength of FSWedjoints depends on the process parameters, a new method was used in this study to predict the tensile behavior of friction stir welded AA5083 and AA2024 aluminum alloy joints in terms of tensile elongation (TE) and ultimate tensile strength (UTS). A new metaheuristic algorithm called Marine Predators Algorithm (MPA) has been integrated with Random Vector Functional Link (RVFL) network to improve the prediction accuracy. Rotational speed, welding speed, tool axial force, and pin profile were used as input parameters while UTS and TE works as the corresponding outputs. The MPA-RVFL model was tested and validated,a great agreement was demonstrated between the experimental results and the predicted results indicating that the developed technique is accurate and reliable to predict the tensile behavior of welded aluminum joints.

The effects of stacking sequence on drilling machinability of filament wound hybrid composite pipes: Part-1 mechanical characterization and drilling tests

Abstract: In the first part of this two-part comprehensive study, mechanical properties and machinability characteristic of filament wound hybrid composite pipes with various stacking sequences of glass and carbon fibers (Glass-Carbon-Glass (GCG), Carbon-Glass-Glass (CGG), and Glass-Glass-Carbon (GGC)) were investigated experimentally. In order to determine the mechanical properties of the pipes, hardness test (Shore D), ring tensile test (ASTM D2290), and burst test (ASTM D1599) were carried out. Machinability tests were performed at various feed rates (50, 150, 250 and 350 mm/min) and spindle speeds (796, 1592, 2388 and 3184 rpm) using with and without a back-up. The results showed that stacking of the carbon layer between two glass layers (GCG) presented better performance in terms of mechanical properties and machinability characteristic. The maximum ring tensile stress of GCG specimen is 27% and 19% higher than those of GGC and CGG specimens, respectively. On the other hand, the lowest thrust forces measured during the drilling of GCG specimen while the GGC represented highest values. In addition, the use of back-up led to an increase in thrust force. The highest increase was observed in GGC sample. In GGC sample, a change in a spindle speed increased thrust force by 18–35%, while a change in feed rate increased thrust force by 20–30%.

Comparative study on the mechanical, tribological, morphological and structural properties of vortex casting processed, Al–SiC–Cr hybrid metal matrix composites for high strength wear-resistant applications: Fabrication and characterizations

Abstract: The cast aluminum-silicon alloys are used to make various automobile components like pistons, cylinder blocks, piston insert rings, connecting rod, brake disc, etc. but low strength, hardness, and wear resistance restricted their use in several applications. Silicon carbide reinforced aluminum matrix composites exhibit better properties than base metal alloys. As an alloying element, the chromium improves the hardness, strength, and elastic limit of the steel. In this study, the characterization of Al-Si alloy-based metal matrix composites that are reinforced with silicon carbide and chromium is performed with the help of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), microhardness test, tensile test, sliding wear test, scratch test, and porosity analysis. The aluminum matrix composites with a varying weight percent of chromium (0-3 wt.% in steps of 1.5) and a fixed percentage of silicon carbide (10%) were formulated through the vortex casting process. The SEM and EDS images illustrate the occurrence and somewhat uniform dispersion of the reinforcement particulates. In hybrid composites, the Cr3C2 compound formation is observed with the least intensity. The reinforcement content contributes significantly to improve the hardness, strength, abrasion resistance, and wear resistance along with a modest reduction in the ductility and gain in friction coefficient. The porosity level obtained in the composites revealed that composites are free from casting defects.

Size-dependent stochastic tensile properties in additively manufactured 316L stainless steel

Abstract: Recent work in metal additive manufacturing (AM) suggests that mechanical properties may vary with feature size; however, these studies do not provide a statistically robust description of this phenomenon, nor do they provide a clear causal mechanism. Because of the huge design freedom afforded by 3D printing, AM parts typically contain a range of feature sizes, with particular interest in smaller features, so the size effect must be well understood in order to make informed design decisions. This work investigates the effect of feature size on the stochastic mechanical performance of laser powder bed fusion tensile specimens. A high-throughput tensile testing method was used to characterize the effect of specimen size on strength, elastic modulus and elongation in a statistically meaningful way. The effective yield strength, ultimate tensile strength and modulus decreased strongly with decreasing specimen size: all three properties were reduced by nearly a factor of two as feature dimensions were scaled down from 6.25 mm to 0.4 mm. Hardness and microstructural observations indicate that this size dependence was not due to an intrinsic change in material properties, but instead the effects of surface roughness on the geometry of the specimens. Finite element analysis using explicit representations of surface topography shows the critical role surface features play in creating stress concentrations that trigger deformation and subsequent fracture. The experimental and finite element results provide the tools needed to make corrections in the design process to more accurately predict the performance of AM components.

Permeation Damage of Polymer Liner in Oil and Gas Pipelines: A Review.

Abstract: Non-metallic pipe (NMP) materials are used as an internal lining and standalone pipes in the oil and gas industry, constituting an emerging corrosion strategy. The NMP materials are inherently susceptible to gradual damage due to creep, fatigue, permeation, processing defects, and installation blunder. In the presence of acid gases (CO2, H2S), and hydrocarbons under high pressure and temperature, the main damage is due to permeation. The monitoring of possible damage due to permeation is not well defined, which leads to uncertainty in asset integrity management. Assessment of permeation damage is currently performed through mechanical, thermal, chemical, and structural properties, employing Tensile Test, Differential Scanning Calorimetry (DSC), Fourier-transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM)/Transmission Electron Microscopy (TEM), to evaluate the change in tensile strength, elongation, weight loss or gain, crystallinity, chemical properties, and molecular structure. Coupons are commonly used to analyze the degradation of polymers. They are point sensors and did not give real-time information. Polymers are dielectric materials, and this dielectric property can be studied using Impedance Analyzer and Dielectric Spectroscopy. This review presents a brief status report on the failure of polymer liners in pipelines due to the exposure of acid gases, hydrocarbons, and other contaminants. Permeation, liner failures, the importance of monitoring, and new exclusive (dielectric) property are briefly discussed. An inclusive perspective is provided, showing the challenges associated with the monitoring of the polymer liner material in the pipeline as it relates to the life-time prediction requirement.