Monotonic Tensile Tests Research Articles

Study on hysteretic performance of welded T-joints circular tube on platform considering seawater corrosion

In this study, the macroscopic hysteretic mechanical behaviour of welded circular tube T-joints corroded by seawater was evaluated through hysteretic mechanical performance tests. Full immersion accelerated electrochemical corrosion tests with a proportioned seawater medium were conducted on steel specimens obtained from tube joints. The generalised degradation rule of the mechanical performance of the material with the development of corrosion was obtained via a monotonic tensile test of steel specimens. The hysteresis test of corroded joints revealed that corrosion and cyclic loading have degradation effects on joint strength, stiffness, bearing capacity, and energy dissipation. At a low number of cycles, the effect of corrosion is generally greater than that of cyclic loading. A hysteretic skeleton model that can determine the ultimate load of the corroded joint was established based on the load–displacement curve. Moreover, the hysteretic rules that describe the degradation characteristics of the loading and unloading stiffness were established. Finally, the hysteresis model of corrosion joints was proposed. The model was validated using experimental results, and we demonstrated that it can accurately reflect the effect of the degree of corrosion and loading process on the hysteretic characteristics of joints.

Effect of local corrosion on tensile behavior of steel plates

Steel structures are susceptible to local corrosion due to the reasons such as the failure of anticorrosive coating, which is a serious threat to the normal use of steel structures, and even causes some tragic accidents. This paper focused on the tensile behavior of locally corroded steel plates. To develop the critical data of such steel plates, uniformly corroded and locally corroded steel plate specimens with different corrosion periods were prepared by artificially accelerated salt spray test. Subsequently, monotonic tensile tests were carried out on a total of 51 corroded and uncorroded specimens. The results revealed that the load–displacement curves of corroded specimens were significantly different from that of uncorroded specimens. In addition, the uniform corrosion had little effect on the actual stress of specimens, while the fully yield stress of the locally corroded specimens was clearly higher than that of uncorroded specimens due to stress concentration. Whereafter, an empirical formula with surface roughness parameters for predicting the elongation degradation of the locally corroded tensile steel plate was proposed based on the previous studies and the experimental data in this research. Finally, the finite element model of the locally corroded specimen under monotonic tensile load was established and the stress distribution in the local corrosion region was analyzed, which demonstrated that the maximum corrosion depth had a substantial effect on the stress concentration.

Identification of the anisotropic behavior of the laser welded Interstitial Free steel HC260Y subjected to uniaxial tensile tests

The main purpose of this paper is to study the anisotropic behavior of laser welded interstitial free steel HC 260Y when it is subjected to monotonic tensile tests. The specimens were cut in different orientations according to the rolling direction, annealed and finally assembled by laser welding. The plastic behavior was modelled using an identification strategy based on a behavior law taking into account the anisotropy of this material, a hardening law describing the evolution of the hardening curves and an evolution law. The proposed identification strategy allowed for a good validation of the model. The model was afterwards used to predict the behavior of the welded material when it is subjected to various solicitations. Finally, the fracture surfaces of the specimens were examined using the scanning electron microscope (SEM) to determine the failure characteristics under the tensile loading.

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.

Orientation dependent plastic localization in the refractory high entropy alloy HfNbTaTiZr at room temperature

A statistical and quantitative perspective on the incipient slip localization behavior of the HfNbTaTiZr refractory high entropy alloy is presented, after monotonic tensile testing at room temperature. High-resolution digital image correlation (HR-DIC) data collected in the scanning electron microscope (SEM) is coupled with electron back-scattered diffraction (EBSD) over millimeter-scale fields of view containing over a hundred crystal orientations. Two populations of grains are identified with respect to their slip localization: a vast majority of the grains exhibit a high density of apparently straight slip bands of low intensity, while the remaining grains show few but very intense and wavy slip bands at the mesoscopic scale. The slip localization behavior is strongly correlated to the crystal orientation with respect to the loading direction. This behavior is discussed with regard to dislocation glide and cross-slip processes.

Effects of Grout Compactness on the Tensile Behavior of Grouted Splice Sleeve Connectors

The quality of grouted sleeve has a significant influence on the performance of the sleeve splice. Incompactness of the infilled grout is inevitable in sleeve grouting. To investigate the tensile behavior of grouted splice sleeves due to different grout compactness, monotonic tensile tests on grouted splice sleeve connectors were performed at grout compactness of 100%, 90%, 70%, and 50%, respectively. The bond-slip analytical model of rebar-grout was deduced by fitting the tensile test data, and the formula for the tensile capacity of the grouted splice sleeve was proposed in the paper. The results show that the tensile strength of the splice sleeve reduces as the grout compactness decreases. It was found from the experiment that the calculated values of tensile capacity are in good agreement with the experimental values. The proposed formula can be adopted in determining whether reinforcing remedies or re-grouting should be taken in the case of incompact grout in grouted splice sleeve connectors.

Combination of cellulose and plant oil toward sustainable bottlebrush copolymer elastomers with tunable mechanical performance

In this work, sustainable cellulose-g-poly(lauryl acrylate-co-acrylamide) [Cell-g-P(LA-co-AM)] bottlebrush copolymer elastomers derived from cellulose and plant oil were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Differential scanning calorimeter (DSC) results indicate that these thermally stable Cell-g-P(LA-co-AM) bottlebrush copolymer elastomers show adjustable melting temperatures. Monotonic and cyclic tensile tests suggest that the mechanical properties, including tensile strength, extensibility, Young's modulus, and elasticity, can be conveniently controlled by changing the LA/AM feed ratio and cellulose content. In such kind of bottlebrush copolymer elastomers, the rigid cellulose backbones act as cross-linking points to provide tensile strength. The incorporated PAM segments can form additional network structure via hydrogen bonding, resulting in enhanced tensile strength but decreased extensibility when more PAM segments are introduced. This versatile strategy can promote the development of sustainable cellulose-based bottlebrush copolymer elastomers from renewable resources.

Consideration of a Tack Coat Bond Strength Test to Minimize the Potential for Slippage Failures on Flexible Airfield Pavements

Slippage failures on flexible pavements are a potential problem for airports given the large wheel loads and high tire pressures of modern aircraft. While not common, when slippage failures do occur the impact can be significant on flexible pavement performance. This paper has three components: (1) case studies of slippage failures that have occurred on airfield pavements; (2) a literature review of relevant interlayer bond strength test procedures; and (3) the results of an analytical, field, and laboratory research investigation. Component (3) was conducted to assess the suitability of interface bond strength tests to evaluate the sufficiency of interlayer bond strength between lifts of asphalt pavement, either new construction or an overlay of existing pavement. The analytical study found that for a fully bonded pavement (no-slip condition), subgrade strength was the primary factor affecting horizontal stress at the interface followed by wheel load. Field cores were obtained from recently constructed asphalt pavements and brought to the laboratory for monotonic direct shear testing to determine bond strength as well as monotonic indirect tensile testing to determine mixture strength. Testing was conducted at 77°F (25°C) and 136°F (58°C). Results showed better repeatability at room temperature with similar relative performance ranking to the critical case high temperature test. Bond strength was influenced by in-place mixture density. Overall, the bond strength test method was practicable for use in field laboratories for acceptance testing.

Modeling and experimental study on electrical impedance response to damage accumulation in 2D C/SiC composites

The electrical properties of C/SiC composites could be used for online and in-situ damage monitoring. To investigate alternating current (AC) impedance response to damage in the C/SiC composites, monotonic and incremental cyclic tensile tests were performed. Both AC impedance and acoustic emission (AE) techniques were applied to clarify the damage evolution during the tests. The relationship between damage and electrical impedance response was investigated and validated via macroscopic equivalent circuit models. The effects of longitudinal deformation and damage on AC impedance characteristics, including impedance magnitude and phase angle, were obtained from the models. Results showed that the longitudinal deformation increases the impedance magnitude and the phase angle, and the damage causes the impedance magnitude to increase and the phase angle to decrease. The phase angle is significantly sensitive to fiber breakage, which makes the AC-based method more suitable for online damage monitoring and final failure warning.

Characterization methods for strain‐induced damage in polypropylene

AbstractVarious methods are used to characterize the deterioration of mechanical properties in polymers. The focus is set on distinguishing between time‐dependent and irreversible damage in two different grades of polypropylene. First, digital image correlation is utilized to capture the stress–strain behavior during monotonic tensile tests. Changes in specimen volume are recorded throughout the experiment and serve as an indicator for crazes and voids. However, the elastic modulus, E, cannot be monitored throughout the entire experiment. Further analysis is performed in the form of cyclic load–unload tests. E and the residual strain, εres, as a function of the applied strain, εappl, are obtained for each cycle. Results show that E primarily suffers from the time‐dependent behavior of the tested polymers in this case. Subsequently, an alternative technique is applied, where specimens are prestrained and then allowed to relax. In the following dynamic mechanical analysis, viscoelastic effects can be avoided. Considerations on the onset and evolution of damage are made. Ultimately, these results are confirmed through microcomputed tomography, where the shapes and densities of defects are captured in high resolution.

Effect of pre-fatigue damage on static and hysteretic behavior of Q355 steel

The mechanical behavior and low cycle fatigue properties of Q355B structural steel subjected to different levels of pre-fatigue damage were investigated in the present study. Monotonic tensile and low cycle hysteresis loading tests were carried on Q355B steel coupons with pre-fatigue damage to investigate its influence on the mechanical properties of Q355B steel. A reliable relationship between the mechanical behavior and the pre-fatigue damage under cyclic loading was subsequently established. The findings from the present research provide a valuable reference for the accurate assessment of the mechanical performance of steel structures after varying degrees of pre-fatigue damage.

An Investigation on Fatigue Resistance of Notched Long Fiber-Reinforced Composite Materials

A new type of specimen is proposed for further research on the structure of glass-fiber-reinforced resin matrix composite lamina, which holds the potential to significantly improve the fatigue property of materials while having limited effect on the tensile strength. Herein, the fatigue life, based on the monotonic tensile test, was simulated utilizing ANSYS and nCode analysis software. The results show that the tensile strength of the local notched fiber specimens is slightly lower than that of the continuous long-fiber specimens. However, when extending the notches’ longitudinal distance, the impact to tensile strength becomes smaller and smaller. The results show that, when the longitudinal distance of the notched fiber is greater than 80 mm, the reduction in tensile strength is less than 0.65%. At the same time, the fatigue property of the specimens is improved considerably. It has been found in this experiment that when the notches’ longitudinal distance is 100 mm, the notches’ length is 1.5 mm, and the notches’ width is 1.75 mm, the fatigue cycles number of the specimens reaches 126,000 cycles, which is about 180% higher than that of the 0-0 type long fiber specimens without notches. This investigation provides a robust foundation and is a compelling basis for further exploration of new fatigue specimens.

Viscoelastic-viscoplastic modeling of epoxy based on transient network theory

The expansion of the application of polymers instead of metals has warranted the evaluation and modeling of their mechanical behaviors under various conditions. In the present study, the strain-rate- and temperature-dependent nonlinear mechanical behavior of a glassy polymer from small to large strain ranges is investigated experimentally and numerically. The effects of strain rate and temperature on the mechanical responses and development of the strain field under monotonic and cyclic uniaxial tensile tests of epoxy are evaluated experimentally. In addition, the stress relaxation test is performed to evaluate the time-dependent mechanical behavior of epoxy. In the previous work (Uchida et al. 2019), the concept of the transient network (TN) theory was applied to demonstrate the nonlinear behavior of the thermosetting glassy polymer. In this model, the time-dependent mechanical behavior of the thermosetting glassy polymer was assumed to be characterized by the debonding and rebonding of intermolecular secondary bonds (SBs). In the present study, the TN model is extended to represent the temperature- and strain rate-dependent mechanical behavior of the thermosetting glassy polymer below the glass transition temperature Tg. The decrease in the deformation resistance of a polymer at a higher temperature is represented by a decrease in the SB density. Furthermore, the fixation parameter is introduced to accurately predict the residual strain in the cyclic tensile test. The mechanical responses in the monotonic and cyclic tensile tests and the stress relaxation test predicted by the extended TN model are consistent with the experimental results. The proposed model is further verified using additional experimental results provided in references. The obtained results demonstrate the nonlinear deformation behaviors of glassy polymers under wide ranges of temperature and strain rate.

Multiaxial fatigue life assessment of 304 austenitic stainless steel with a novel energy-based criterion

A novel energy-based multiaxial fatigue criterion was proposed considering the effect of normal strain energy and shear strain energy. The difference of contributions of both the normal strain energy and shear strain energy on the failure of materials was identified by introducing the stress-path-dependent energy weight coefficient. A newly defined non-proportionality based on the stable hysteresis loops was introduced to the criterion considering the non-proportionality additional hardening behavior. Most of the coefficients can be determined by the monotonic tensile test which gives more opportunities for the applicability and feasibility of the new criterion in engineering practice. The performance of the new criterion was approved by comparing the predicted and tested life of SS304 under various multiaxial loading paths.

Metallic materials fatigue behavior: Scale levels and ranges of transition between them

The metal fatigue behavior is analyzed on the basis of the multi-scale description of damage accumulation processes in direction of increasing scales (from micro- to meso- and macroscopic scale levels). The governing mechanisms in the damage accumulation process peculiar to each scale level are considered. The transitions between scales are realized gradually within the ranges with the bimodal distribution of fatigue life. Statistical analysis of data on mechanical characteristics defined in monotonic tensile and fatigue tests for aviation structural materials based on Fe, Al, Mg, Ti, Cu, and Ni have shown that for most alloys the three scale levels are exhibited in the direction of the stress level increasing.

Precipitation kinetics and crystal plasticity modeling of artificially aged AA6061

An artificially aged AA6061 alloy was investigated at multiple heat treatment conditions with monotonic tensile and cyclic shear testing to characterize the effect of precipitation on the alloy's mechanical properties. The microstructure was first measured with scanning electron microscopy, which was observed to remain fairly constant throughout all aging conditions. Mechanical testing showed that artificial aging reduced the initial work hardening rate without affecting dynamic recovery. The alloy also exhibited a reduction in plastic anisotropy and an increase in kinematic hardening with increased aging time. Afterwards, a numerical through-process framework was introduced to predict both the precipitation kinetics and mechanical behavior of AA6000-series materials. The kinetics model was calibrated and validated with transmission electron microscopy measurements on several Al-Mg-Si alloys. The mechanical model uses the simulated precipitate distribution in a modified crystal plasticity framework to calculate the alloy's constitutive response. The framework was able to simulate the yield strength, work hardening, plastic anisotropy and Bauschinger behavior of AA6061 with reasonable accuracy. Plastic anisotropy and kinematic hardening was specifically captured with an inclusion-based method of modeling the precipitates. The model was later used to simulate precipitation hardening in individual single crystals. It was observed that the effect of artificial aging is minor compared to the overall effect of texture on the material.

Mechanical properties of plate type steel bar connectors for prefabricated concrete structures

This article presented experimental studies on mechanical properties on Plate Type steel Rebar Connector (PTRC), which is composed of steel plate, thread coupler, and steel tube. This is a new method of mechanical connection of steel bars provided in this article for full-precast concrete shear wall structures. The proposed PTRC was tested under monotonic tensile tests, high-stress cyclic tests and high-deformation cyclic tests according to the code (JGJ107-2016). PTRCs were evaluated as Grade I splice through U0, U4, U8, Asgt, and U20 according to the code. The stress distribution curves and end section rotation of PTRCs with different parameters were analyzed using verified Finite Element Model. The calculation methods of PTRC initial stiffness, including stiffness of bolt and threads were provided.

Ultimate tensile behavior of bolted stiffened T-stub connections in progressive collapse resistance

This paper investigates the ultimate tensile behavior of the bolted stiffened T-stub connections using experimental, numerical, and analytical methods. The monotonic tensile tests were carried out on sixteen bolted stiffened T-stub connections with different parameters to investigate the failure mode, yield line distribution, and key mechanical properties of them. The results showed that the distribution pattern of the yield line along the center of the bolt holes changed with the increase of the stiffened T-stub thickness and the longitudinal bolt pitch. The effect of the longitudinal bolt pitch on the ultimate strength of the connection was non-monotonic. Finite element models of the bolted stiffened T-stub connections were established and validated to conduct the parametric analysis. The simulation results showed that increasing the thickness ratio between the vertical plate and the horizontal plate could improve the ultimate strength of the connection. Based on the experimental and parametric studies, the prediction methods for the ultimate strength and initial stiffness of the stiffened T-stub connections with or without bolt pretension were proposed and validated against the experimental data and other prediction methods.

Effects of weld geometry and HAZ property on low-cycle fatigue behavior of welded joint

A previous experimental study by the authors clearly indicated that, due to the delay of the crack initiation, the butt-welded joint with smoother weld toe profile and harder weld metal had a longer low-cycle fatigue life. In the present study, supplementary numerical studies considering weld geometries and inhomogeneous mechanical properties are executed. Monotonic tensile and strain-controlled low-cycle fatigue tests on the reheated round bars are firstly conducted to characterize the mechanical properties for different zones of the butt-welded joints. The test results are used to calibrate the material constitutive model, which is then embedded into three-dimensional finite element models to investigate the low-cycle fatigue behavior of the butt-welded joints. The numerical results suggest the necessity of considering the effects of inhomogeneous material properties when evaluating the low-cycle fatigue of welded joints. It is also confirmed that decreasing weld toe stress concentration and simultaneously increasing weld metal strength can maximally increase the low-cycle fatigue life of welded joints compared to the individual changes for either one. These findings are expected to provide some insights into the low-cycle fatigue life improvement of welded joints.

Microstructural characterization and mechanical properties of additively manufactured 17–4PH stainless steel

The aim of the present study is to carry out a comprehensive microstructural characterization on the Selective Laser Melting (SLM) printed 17–4PH stainless steel and to compare the results with commercial 17–4PH wrought alloy (in H1150 condition). It was found out that the middle region of as-printed SLM had less microporosities as compared to bottom and top regions which was attributed to the lower cooling rate in the middle-area and greater extent of fusion during manufacturing. The as-printed samples mainly consist of ά-martensite and retained austenite (γ). The electron back scatter diffraction (EBSD) results showed that the middle region had less retained austenite as compared to top and bottom ones. The fraction of high angle grain boundaries (HAGB) and twin boundaries (TB) in martensite in wrought alloy was found to be greater than the as-built samples. In contrast, a high fraction of HAGBs and low fraction of TBs were observed in austenite in as-printed samples. The SEM-TKD revealed that the fraction of phase boundaries close to Kurdjumov–Sachs (KS) orientation relationship (OR), i.e., x < 10°, was 93.3% and 91.73% for the wrought alloy and SLM printed, respectively. The average Vickers hardness of as-printed sample was ≈ 25% less than the commercial wrought alloy (in H1150 condition) which can be attributed to more retained austenite, larger grain size, and more microporosities in the matrix. Monotonic uniaxial tensile test and in-situ tensile deformation with the aid of EBSD were used to examine the mechanical strength of wrought and SLM samples and microstructural evolution during plastic deformation. The ultimate tensile strength (UTS) of the as-printed sample (≈1118 ± 4 MPa) was quite comparable to commercial alloy (1017 ± 2 MPa) but the uniform elongation was considerably higher in as-printed sample (21.8% ± 0.3 in as-printed versus 9.00% ± 0.56 in wrought alloy). EBSD analysis during the in-situ tensile test showed transformation induced by plasticity (TRIP effect) of γ → ά. The area fraction of retained austenite in SLMed sample decreased from 26.2% in stage I (zero strain) to 0.49% in stage IV (failure). Lath and acicular shape retained austenite transformed faster to martensite than the blocky shape austenite.