Monotonic Tensile Behavior Research Articles

Varying strain rates and elevated temperatures effects on the mechanical properties of AZ31B magnesium alloy

This study investigates the monotonic tensile behavior of magnesium (Mg) alloy AZ31B across a temperature range from ambient (25 °C) to elevated (up to 300 °C) with varying strain rates (SR) (1.5 × 10−2 to 1.5 × 10−4 s−1). Mechanical properties such as ultimate tensile strength ( σu), tensile yield strength ( σy), strain to failure ( εf), plastic anisotropy ( r-value), strain rate sensitivity ( m) and strain hardening exponent ( n) were investigated in this study for these strain rates. As the temperature increased from 25 to 300 °C, the following changes in mechanical properties were observed: the yield strength ( σy) decreased by 84.50%, the ultimate tensile strength ( σu) decreased by 87%, the modulus of elasticity ( E) decreased by 63.0%, and the elongation increased by 72.0%. The reduction factors (RF) were proposed for the above-mentioned mechanical properties for varying temperature ranges. The impact of varying temperatures and strain rates on fracture surfaces was investigated using field emission scanning electron microscopy (FE-SEM). The results revealed the presence of tenacity nets, cleavage patterns, and an increasing number of dimples as temperatures increased.

Bolted steel to laminated timber and glubam connections: Axial behavior and finite-element modeling

This study aims to characterize the axial monotonic and cyclic tensile behavior of bolted steel connections to laminated timber and bamboo, using slotted-in steel plates, and to provide a high-fidelity simulation using finite-element modeling. Forty-eight experimental tests were conducted, including eight different configurations, varying in material (Laminated Veneer Lumber (LVL) and Glued Laminated Bamboo (glubam)), number of bolts, and diameter of bolts, under tension, both monotonic and cyclic (three repetitions). The force and displacement were recorded, and used to define the initial stiffness, yielding strength, ultimate strength, ductility, viscous damping, and energy dissipation. The failure modes of the connections were monitored using Digital Image Correlation (DIC) techniques. A novel high-fidelity finite-element model integrating Hill’s yielding and element removal criteria was proposed to predict the mechanical performance and fracture behavior of the examined connections. The numerical simulation was validated by comparing the experimental load–displacement curves and the strain field measurements obtained with DIC. Finally, theoretical formulas for predicting the stiffness of bolted connections were proposed based on the FEM simulations.

Novel austenitic Cr-Mn-Ni TWIP-steel with superior strength enabled by laser powder bed fusion – On the role of substrate temperatures

• PBF-LB/M of the investigated steel dramatically improves the monotonic tensile behavior compared to the conventionally-cast material. • While UTS is nearly unaffected by a variation of substrate temperatures, the YS decreases, whereas work hardening and elongation at fracture are increased. • Such behaviour is well suited for robust PBF-LB/M processing, i.e. minor changes in the overall process do not promote pronounced changes in mechanical behaviour. • Irrespective of substrate temperature, the material exhibits an appealing strength-ductility combination In the present study, a novel austenitic stainless Cr-Mn-Ni steel was processed using laser-based powder bed fusion of metals (PBF-LB/M) at substrate plate temperatures ranging between 20 °C and 500 °C. Microstructure evolution was analysed by means of electron backscatter diffraction (EBSD). Different substrate plate temperatures lead to differences in microstructure evolution due to the prevailing cooling conditions and overall thermal history, eventually resulting in different hardening behavior under quasi-static tensile loading even if the general mechanical performance of the different conditions is very similar. From the results shown, it is deduced that the prevailing microstructures are a result of different internal stress states evolved during solidification, cooling and intrinsic heat treatment, respectively. The different internal stress states promote increased local orientation deviations within the grains, which can be rationalized by different dislocation densities. The monotonic strength of the steel in focus is outstanding compared with cold-rolled counterparts and data available in literature.

Experimental and numerical investigations on monotonic tensile behavior of grouted sleeve couplers with different splicing configurations

This study presents experimental and numerical investigations on the tensile behavior of grouted sleeve (GS) couplers splicing steel bars with transition splicing and different strength grades intended for use in shifted plastic hinge applications. Sixteen GS specimens, with testing parameters that included GS coupler size, steel bar diameter, and transition splicing index, were assembled and tested under static monotonic tensile tests. Also, one-dimensional finite element (FE) modeling was conducted to establish the bond–slip constitutive models, which govern the bar–grout interfaces at different regions of the GS coupler, by inverse analysis.Experimental results showed consistent failure mode, which was bar rupture away from the coupler region, for all splicing configurations of GS couplers, which demonstrated the ability of GS couplers to fully develop the ultimate stress in the spliced bars. Results also revealed an approximately piecewise linear relationship that governs the ratio between the strain within the coupler region and strain in the spliced normal strength steel bar, in which the strain ratio decreases with larger sleeve sizes and higher transition indices. Furthermore, results showed that GS couplers exhibited considerable slip that increased with bar size and can be of benefit to GS precast members that are subjected to significant rotation demands. The proposed bond–slip models for GS couplers were simple but accurate in slip prediction and they can be very helpful in the analytical modeling of precast members containing GS couplers.

Low Cycle Fatigue Performance of Additively Processed and Heat-Treated Ti-6Al-7Nb Alloy for Biomedical Applications

In biomedical engineering, laser powder bed fusion is an advanced manufacturing technology, which enables, for example, the production of patient-customized implants with complex geometries. Ti-6Al-7Nb shows promising improvements, especially regarding biocompatibility, compared with other titanium alloys. The biocompatible features are investigated employing cytocompatibility and antibacterial examinations on Al2O3-blasted and untreated surfaces. The mechanical properties of additively manufactured Ti-6Al-7Nb are evaluated in as-built and heat-treated conditions. Recrystallization annealing (925 °C for 4 h), β annealing (1050 °C for 2 h), as well as stress relieving (600 °C for 4 h) are applied. For microstructural investigation, scanning and transmission electron microscopy are performed. The different microstructures and the mechanical properties are compared. Mechanical behavior is determined based on quasi-static tensile tests and strain-controlled low cycle fatigue tests with total strain amplitudes εA of 0.35%, 0.5%, and 0.8%. The as-built and stress-relieved conditions meet the mechanical demands for the tensile properties of the international standard ISO 5832-11. Based on the Coffin–Manson–Basquin relation, fatigue strength and ductility coefficients, as well as exponents, are determined to examine fatigue life for the different conditions. The stress-relieved condition exhibits, overall, the best properties regarding monotonic tensile and cyclic fatigue behavior.

Characterization of the Fatigue Behavior of SLS Thermoplastics

The selective laser sintering (SLS) is an additive manufacturing technology with clear potential for producing high quality polymeric components of various thermoplastic polymers and elastomers which can be used in demanding engineering applications under complex service loading conditions. The prerequisite for these applications is that the stiffness and the tensile strength of the SLS specimens is in the same range as for injection molded specimens using a proper parameter set of the SLS process and qualified materials. While the tensile strength of SLS printed polymers is recently determined by many researchers, hardly any data are available about the fatigue behavior of SLS polymers on specimen level and even less on component level. Cylindrical specimens with and without round notch have been designed and additively manufactured using PA12 and TPU SLS grades in two different printing directions (vertical and horizontal). The monotonic tensile behavior was characterized over a wide loading rate range (0.1 to 100 mm/s) and the tensile strength and failure strain values were determined. The fatigue behavior was characterized under cyclic loading conditions at various stress ratios (R=0.1, -1), at a constant frequency of 5 Hz at 5 stress levels. Stress vs. cycle number-to-failure, Nf points were determined for constructing conventional S-N curves for the materials investigated. A distinct anisotropy of the tensile strength and failure strain was recognized for the SLS TPU investigated.

Tensile Behavior of High-Density Polyethylene Including the Effects of Processing Technique, Thickness, Temperature, and Strain Rate.

The primary goal of this study was to investigate the monotonic tensile behavior of high-density polyethylene (HDPE) in its virgin, regrind, and laminated forms. HDPE is the most commonly used polymer in many industries. A variety of tensile tests were performed using plate-type specimens made of rectangular plaques. Several factors can affect the tensile behavior such as thickness, processing technique, temperature, and strain rate. Testing temperatures were chosen at −40, 23 (room temperature, RT), 53, and 82 °C to investigate temperature effect. Tensile properties, including elastic modulus, yield strength, and ultimate tensile strength, were obtained for all conditions. Tensile properties significantly reduced by increasing temperature while elastic modulus and ultimate tensile strength linearly increased at higher strain rates. A significant effect of thickness on tensile properties was observed for injection molding specimens at 23 °C, but no thickness effect was observed for compression molded specimens at either 23 or 82 °C. The aforementioned effects and discussion of their influence on tensile properties are presented in this paper. Polynomial relations for tensile properties, including elastic modulus, yield strength, and ultimate tensile strength, were developed as functions of temperature and strain rate. Such relations can be used to estimate tensile properties of HDPE as a function of temperature and/or strain rate for application in designing parts with this material.

Toward low and high cycle fatigue behavior of SLM-fabricated NiTi: Considering the effect of build orientation and employing a self-heating approach

Build orientation is one of the important parameters in the selective laser melting (SLM) process that could alter the mechanical and fatigue properties of the fabricated parts. In the first section of this paper, the monotonic tensile and low-cycle fatigue behavior of the SLM NiTi dog-bone samples fabricated in three different orientations are investigated. Based on the results, the highest fatigue life was for the samples fabricated in 45° with respect to the build plate, and the lowest fatigue life was for the samples fabricated on their edge. Furthermore, horizontally fabricated samples showed the highest scatter in fatigue life. It was revealed using SEM analysis that based on the build orientation, different types of defects, such as lack of fusion, entrapped gas porosities, and surface flaws could be generated inside the parts that could lead to a premature failure. In the second section of the paper, for the first time, the self-heating approach is utilized to investigate the high-cycle fatigue behavior of SLM NiTi samples fabricated in the horizontal direction. By considering the same origin for the fatigue damage and the one that generates the heat dissipation, self-heating approach can be used to predict the fatigue properties of the material. Using the self-heating approach, the fatigue limit for the virgin as well as pre-strained samples were evaluated. Similar to the conventional metals, the pre-strained sample showed a higher mean fatigue limit in comparison with the virgin samples.

Powder Recycling Effects on the Tensile and Fatigue Behavior of Additively Manufactured Ti-6Al-4V Parts

Additive manufacturing technology has enabled industries to generate functional parts with an increased level of complexity via layer-by-layer fabrication. In laser-powder bed fusion (L-PBF), powder is often recycled due to its high cost. However, there is no comprehensive study on how powder recycling affects its rheological properties, as well as the mechanical and fatigue behavior of the manufactured part. This study compares powder characteristics and mechanical performance of as-built and machined specimens fabricated from new and heavily used Ti-6Al-4V powder. Powder characteristics include particle size distribution and morphology, flowability, apparent density, compressibility, thermal conductivity, oxygen concentration, and more. Results indicate that particle size distribution becomes narrower and flowability increases with recycling. Not a significant effect of recycling was observed on the monotonic tensile and fatigue behavior of specimens in the as-built surface condition. However, machined specimens fabricated from used powder demonstrated longer fatigue lives in the high cycle regime.

Experimental characterization of the tensile strength of ABS parts manufactured by fused deposition modeling process

Acrylonitrile–butadiene–styrene (ABS) is one of the most widely usedindustrial thermoplastic and it is the most common material used in fused deposition modeling (FDM) technology. While FDM is one of the most used additive manufacturing (AM) technology commonly employed formodeling, prototyping, and manufacturing applications, the major research issues have been to balance ability to produce aesthetically appealinglooking products with functionality. It is therefore critical to know the mechanical properties of these parts, which, is as expected different from their nominal values.A FDM manufactured part has an internal channel referred to as infill. This internal build pattern has different mechanical properties than the same shaped part without the internal channel. This paper aims to define the effect of specimen mesostructure on the monotonic tensile behavior of ABS parts manufactured by FDM. The experiment uses the uPrint SE 3D printer to produce samples from ABS thermoplastic. The samples are tested following a modified form of ASTM D638 standard for plastic. The printed pieces are tested to failure using an Instron testing machine, and a strain gage extensometer that measures the amount of elongation in the pieces until failure. These standardized pieces are compared to know values of traditionally manufactured materials. This test shows the strength loss of materials through the 3D printing process compared to traditional manufacturing methods. The experiment for plastics is designed around two key criteria, orientation of the pieces, and the percent of infill during the printing process. It was found that a value of maximum strength, of 3D printed ABS, was approximately 92% of accepted values for the material, with a certainty of 5%. The study also shows that the bonds between layers are only 79% as strong as an axil loading along the layers.

Mechanical behavior of post-processed Inconel 718 manufactured through the electron beam melting process

The electron beam melting (EBM) process was used to fabricate Inconel 718. The microstructure and tensile properties were characterized in both the as-fabricated and post-processed state transverse (T-orientation) and longitudinal (L-orientation) to the build direction. Post-processing involved both a hot isostatic pressing (HIP) and solution treatment and aging (STA) to homogenize the microstructure. In the as-fabricated state, EBM Inconel 718 exhibits a spatially dependent microstructure that is a function of build height. Spanning the last few layers is a cored dendritic structure comprised of the products (carbides and Laves phase) predicted under equilibrium solidification conditions. With increasing distance from the build's top surface, the cored dendritic structure becomes increasingly homogeneous with complete dissolution of the secondary dendrite arms. Further, temporal phase kinetics are observed to lead to the dissolution of the strengthening γ″ and precipitation of networks of fine δ needles that span the grains. Microstructurally, post-processing resulted in dissolution of the δ networks and homogeneous precipitation of γ″ throughout the height of the build. In the as-fabricated state, the monotonic tensile behavior exhibits a height sensitivity within the T-orientation at both 20 and 650°C. Along the L-orientation, the tensile behavior exhibits strength values comparable to the reference wrought material in the fully heat-treated state. After post-processing, the yield strength, ultimate strength, and elongation at failure for the EBM Inconel 718 were observed to have beneficially increased compared to the as-fabricated material. Further, as a result of post-processing the spatial variance of the ultimate yield strength and elongation at failure within the transverse direction decreased by 4 and 3× respectively.

Tensile and fatigue behavior of layered acrylonitrile butadiene styrene

Purpose – This paper aims to define the effect of specimen mesostructure on the monotonic tensile behavior and tensile-fatigue life of layered acrylonitrile butadiene styrene (ABS) components fabricated by fused deposition modeling (FDM). Design/methodology/approach – Tensile tests were performed on FDM dogbone specimens with four different raster orientations according to ASTM standard D638-03. Resulting ultimate tensile stresses (UTS) for each raster orientation were used to compute the maximum stress for fatigue testing, i.e. 90, 75, 60 and 50 or 45 per cent nominal values of the UTS. Multiple specimens were subjected to tension – tension fatigue cycling with stress ratio of R = 0.10 in accordance with ASTM standard D7791-12. Findings – Both tensile strength and fatigue performance exhibited anisotropic behavior. The longitudinal (0°) and default (+45/−45°) raster orientations performed significantly better than the diagonal (45°) or transverse (90°) orientations in regards to fatigue life, as displayed in the resulting Wohler curves. Practical implications – Raster orientation has a significant effect on the fatigue performance of FDM ABS components. Aligning FDM fibers along the axis of the applied stress provides improved fatigue life. If the direction of applied stresses is not expected to be constant in given application, the default raster orientation is recommended. Originality/value – This project provides knowledge to the limited work published on the fatigue performance of FDM ABS components. It provides S-N fatigue life results that can serve as a foundation for future work, combining experimental investigations with theoretical principles and the statistical analysis of data.

Study on the Local Mechanical Behavior and Forming Safety of the Clad Steel Plate Used in the Accumulator Tank of Nuclear Plant

The micro-morphology and local mechanical mechanic property parameters of the clad steel plates (304L+533B) used in the accumulator tank of nuclear plant at different temperatures are obtained from the microscopic and macroscopic test. And the monotonic tensile behavior of the clad steel plates and the forming process of the accumulator tank petals are simulated by using the finite element code ABAQUS. Based on the simulations, the validation of the obtained mechanical parameters and the forming safety of the clad steel plates are checked and evaluated. It is shown that the mechanical parameters obtained in this paper are reasonable, and the cold forming process of the rolling clad steel plates (304L+533B) used in the accumulator tank of nuclear plant is safe.

Effect of loading rate and temperature on monotonic tensile behavior in two-dimensional C/SiC composites

The effect of loading rate and temperature on the monotonic tensile behavior of a 2D C/SiC composite was investigated. C/SiC composites with the same area were fabricated by a chemical vapor infiltration and then some were heat-treated (HT) at 1500°C and 1900°C in argon, respectively. The dog-bone shape specimens were machined and subjected to a monotonic tensile test. The results showed that when the loading rate was within 0.0002–0.01mm/s, the strength changed slightly. The failure mode exhibited a transition from brittle to a tough fracture when the loading rate was decreased. The elastic modulus of the as-received, 1500, and 1900°C HT specimens increased by 17.6, 23.1, and 5%, respectively with the rise in loading rate. After HT, the strength and the modulus decreased whereas the work of fracture began to increase, indicating excellent fracture toughness.

Development of a Bamboo-Based Composite as a Sustainable Green Material for Wind Turbine Blades

Bamboo has many engineering and environmental attributes that make it an attractive material for utilization in wind turbine blades. This paper examines the mechanical properties of a novel bamboo-poplar epoxy laminate which is being developed for wind turbine blades. Information provided in this paper includes an overview of the laminate construction and initial data for the monotonic tensile and compressive stress-strain behavior and tension-tension fatigue life of panels formed by hot-pressing. In addition, a discussion of fracture resistance of the bamboo-poplar laminate, under Mode I and Mode II loading conditions is provided.

Tensile behavior of high performance natural (sisal) fibers

Environmental awareness and an increasing concern with the greenhouse effect have stimulated the construction, automotive, and packing industries to look for sustainable materials that can replace conventional synthetic polymeric fibers. Natural fibers seem to be a good alternative since they are readily available in fibrous form and can be extracted from plant leaves at very low costs. In this work we have studied the monotonic tensile behavior of a high performance natural fiber: sisal fiber. Tensile tests were performed on a microforce testing system using four different gage lengths. The cross-sectional area of the fiber was measured using scanning electron microscope (SEM) micrographs and image analysis. The measured Young’s modulus was also corrected for machine compliance. Weibull statistics were used to quantify the degree of variability in fiber strength, at the different gage lengths. The Weibull modulus decreased from 4.6 to 3.0 as the gage length increased from 10 mm to 40 mm, respectively. SEM was used to investigate the failure mode of the fibers. The failure mechanisms are described and discussed in terms of the fiber microstructure as well as defects in the fibers.

Monotonic tensile behavior analysis of three-dimensional needle-punched woven C/SiC composites by acoustic emission

High toughness and reliable three-dimensional needled C/SiC composites were fabricated by chemical vapor infiltration (CVI). An approach to analyze the tensile behaviors at room temperature and the damage accumulation of the composites by means of acoustic emission was researched. Also the fracture morphology was examined by S-4700 SEM after tensile tests to prove the damage mechanism. The results indicate that the cumulative energy of acoustic emission (AE) signals can be used to monitor and evaluate the damage evolution in ceramic-matrix composites. The initiation of room-temperature tensile damage in C/SiC composites occurred with the growth of micro-cracks in the matrix at the stress level about 40% of the ultimate fracture stress. The level 70% of the fracture stress could be defined as the critical damage strength.

Effects of Sulfur Level and Anisotropy of Sulfide Inclusions on Tensile, Impact, and Fatigue Properties of SAE 4140 Steel

During metal forming processes such as rolling and forging, deformable manganese sulfide (MnS) inclusions become elongated. Such elongated MnS inclusions can have considerable adverse effects on mechanical properties, if the inclusions are not aligned with the loading direction. The objectives of this study were to evaluate and compare fatigue, monotonic tensile and CVN impact behavior of SAE 4140 steel with high (0.077% S), low (0.012% S) and ultra low (0.004% S) sulfur contents at two hardness levels (40 HRC and 50 HRC). The longitudinally oriented samples at 40 HRC, where MnS inclusions were oriented along the loading direction, did not exhibit any significant sensitivity of tensile or fatigue properties to the sulfur content. For the transversely oriented MnS inclusions, however, the monotonic tensile test results indicate very low ductility of the high sulfur material at both hardness levels, where specimens failed shortly after yielding. The yield strength of the materials, however, did not differ significantly with the sulfur content. With regards to fatigue strength, the high sulfur material had up to 25% lower fatigue strength than the ultra low sulfur material under transverse loading. The scanning electron microscopy (SEM) inspection of failed fatigue test specimens revealed that the fracture topography of the high sulfur material were very rough and jagged, indicating several cracks originating from MnS inclusions. The fracture surfaces of the other two materials with lower sulfur content exhibited typical fatigue fracture surfaces with clear initiation and final fracture regions.

Effect of loading rate on the monotonic tensile behavior and tensile strength of an oxide–oxide ceramic composite at 1200 °C

The influence of loading rate on monotonic tensile behavior and tensile properties of an oxide–oxide ceramic composite was evaluated in laboratory air at 1200 °C. The composite consists of a porous alumina matrix reinforced with woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tensile tests conducted at loading rates of 0.0025 and 25 MPa/s revealed a strong effect of rate on the stress–strain behavior as well as on the ultimate tensile strength (UTS), elastic modulus and failure strain. At 0.0025 MPa/s, increase in stress results in non-monotonic change in strain, with the rate of change of strain reversing its sign at stresses ∼25 MPa/s. Several samples were subjected to additional heat treatments prior to testing in order to determine whether this unusual stress–strain behavior was an artifact of incomplete processing of fibers in the as-received material. The unusual material response in the 0–30 MPa stress range was further investigated in creep tests conducted with the applied stresses ≤26 MPa. Negative creep (i.e. decrease in strain under constant stress) was observed. Porosity measurements indicate that a decrease in matrix porosity and matrix densification may be taking place in the N720/A composite exposed to 1200 °C at stresses <30 MPa for prolonged periods of time.

Effect of interfacial bonding on uniaxial ratchetting of SiC P/6061Al composites: Finite element analysis with 2-D and 3-D unit cells

The effect of interfacial bonding state between particulate and metal matrix on the ratchetting of SiC particulate reinforced 6061Al alloy composites (i.e., SiC P/6061Al composites) in uniaxial cyclic stressing at room temperature was discussed by numerical simulation using a finite element code ABAQUS. In simulation, axi-symmetrical two-dimensional (i.e., 2-D) mono-particle and three-dimensional (i.e., 3-D) multi-particle unit cells were employed, respectively. The ratchetting of un-reinforced matrix alloy was addressed by an elasto-plastic constitutive model with nonlinear kinematic hardening rule, and the particulates were assumed as elastic. Two kinds of interfacial layers were inserted into the unit cells between particulate and matrix, i.e., elastic and elasto-plastic interfacial layers previously employed by Kang et al. [G.Z. Kang, Q. Gao, Composites A 33 (2002) 657–667] in the numerical simulation for monotonic tensile behavior of short fiber reinforced metal matrix composites. Finally, the ratchetting of T6-treated SiC p/6061Al composites was simulated by using 3-D multi-particle unit cell and suitable interfacial property parameters. It is shown that the simulated results are closer to the corresponding experiments than those obtained with assumption of perfect interface. Simultaneously, some microscopic deformation features in the composites and their evolution rules were also revealed by the numerical simulation. Some significant conclusions are obtained, which are useful to establish a constitutive model to describe the ratchetting of the composites.