Tensile Conditions Research Articles

Study on the Fatigue Strength of Welding Line in Injection Molding Products under Different Tensile Conditions.

The fatigue performance of polypropylene (PP) at various amplitudes and frequencies on fatigue cycles under tensile test conditions is investigated in this study. The results show that increasing the frequency leads to a decrease in fatigue cycles due to increased cycle time. The decline rate can be divided into two stages, between 1 and 5 Hz. The first stage rapidly decreases fatigue performance as the frequency increases from 1 Hz to 2 Hz or 3 Hz. The second stage has a lower reduction rate, which occurs between 2 Hz or 3 Hz and 5 Hz due to the strengthening effect of increasing frequency. Furthermore, increasing the amplitude from 0.1 mm to 0.4 mm reduces the fatigue cycle due to the higher deformation rate. In summary, expanding both amplitude and frequency reduces the fatigue performance of the PP material. Moreover, according to the scanning electron microscope microstructure, increasing the frequency results in more microcracks in the polymer matrix.

Development of order during strain induced crystallization of polymers, case of PET

This study aims at enlightening the kinetics and the nature of the precursor for crystallization in strain induced crystallization (SIC) of PET, combining ex situ and in situ X-ray diffraction on well controlled tensile experiments. Attention is paid too to annealing to assess “stability” of the phases that are generated. It is concluded that SIC in PET consists in the appearance of ordered entities the periodicities of which are those of crystal. Strain hardening corresponds to perfectioning without leading to actual crystal under tension. The kinetics of formation can be directly related to the stress, whatever the set on tensile conditions (temperature, strain rate). However, microstructure of PET can evolve after loading in case of annealing.

The experimental assessment of carbon nanotubes incorporation on the tensile and impact properties of fiber metal laminate fabricated by jute/basalt fabrics-aluminum layers: As hybrid structures

In this work, the simultaneous effect of different stacking sequences of basalt/jute fibers and adding the various weight fractions of carbon nanotubes (CNTs) on the mechanical features of fiber metal laminates (FMLs) under the tensile and impact conditions was assessed. According to the results, the FML had the highest performance under the mechanical tests, when the jute layers were sandwiched by the basalt fibers. In contrast, by sandwiching the basalt fibers with the jute fibers, the FML showed the weakest performance just under the tensile test. This configuration had the moderate performance under the impact test. Incorporating 0.3 wt.% CNTs in all configurations caused to reach the highest improvement in the tensile strength, elastic modulus and impact energy, which were 301 MPa, 50.9 GPa, and 12.3 J, respectively. Reinforcing an adhesion between skin/core and enhancing the mechanical properties of composite core were the effective factors for improving the tensile properties. The delamination of layers, fibrillation of jute fibers, creation of imprint phenomenon, and pull out the basalt fibers were the characterized wasting mechanisms under the impact conditions.

Effect of Bainite/Martensite/Retained Austenite Triplex Microstructure on the High Strain Rate Behavior of a One Step Quenching and Partitioning Steel

The mechanical properties and microstructure evolution of a one step quenching and partitioning steel containing bainite/martensite/retained austenite mixed microstructure was studied though static and dynamic tensile tests (strain rates ranging from10-3 s-1 to 5×102 s-1 ).Scanning electron microscopy (SEM) and electron-back-scattered diffraction (EBSD) were applied to describe the microstructure evolution near the fracture. XRD characterization shows the volume fraction of retained austenite decrease exponentially with the strain rates increased.EBSD phase maps reveal that the first type of retained austenite is less sensitive to strain rate than the second type.

Comparison on mechanical behavior and microstructural features between traditional and AM AISI 316L

AbstractThe aim of the present work is to investigate the difference in mechanical behavior between AISI 316L obtained by the turning process and that obtained by selective laser melting (SLM). To obtain a correlation between mechanical behavior and microstructure, static tensile and fatigue tests were performed, monitoring the energy release of the material adopting, respectively, the static thermographic method (STM) and the Risitano's thermographic method (RTM). Failure analysis was performed using optical and scanning electron microscopy. The corrosion resistance was evaluated by the double‐loop electropotential reactivation (DL‐EPR). Worst mechanical properties, both under static and fatigue loading conditions, loss of corrosion resistance, and heat dissipation compared to traditional stainless steel have been found. These findings can be attributed to microstructural defects typical of the SLM printing technology.

Dynamic impact constitutive relation of 6008-T6 aluminum alloy based on dislocation density and second-phase particle strengthening effects

To investigate the mechanical properties and constitutive relationship of 6008-T6 aluminum alloy under dynamic impact loading, dynamic impact and microscopic experiments were conducted on 6008-T6 aluminum alloy. The results demonstrated that 6008-T6 aluminum alloy exhibits strain hardening effects. As the loading strain rates increased, the grains became more refined, whereas the dislocation density and number of second-phase particles (mainly Mg2Si) increased. Several dislocations interacted with each other, thereby preventing further dislocation movement and improving the material's strength. The precipitation of second-phase particles impeded the motion of dislocations and increased the flow stress of the material. A constitutive model of dynamic impacts was developed based on the evolution of dislocation density and reinforcing effects of second-phase particles. Furthermore, based on the isotropic assumption, the damage evolution equation of 6008-T6 aluminum alloy was obtained by introducing the energy release rate. By combining the dynamic constitutive model of materials under dynamic impact compression conditions, the dynamic constitutive model of materials was obtained under dynamic impact tensile conditions. Moreover, the rationality of the model was confirmed by comparing the model's data with experimental data. In this study, we examined the macro mechanical response, microstructure, and dynamic mechanical behavior of the 6008-T6 aluminum alloy under dynamic impact conditions, which can serve as a theoretical basis and analytical tool for the structural design and safety evaluation of high-speed trains.

COMPARATIVE STUDY OF PARTICLEBOARDS WITH HEVEA BRASILIENSIS WASTE FROM DIFFERENT PRODUCTION AND MOISTURE CONFIGURATIONS

After the production cycle of latex, Hevea brasiliensistrees becomeresidual living plants for this activity, although their woody trunks are still potentially subject to industrial utilization. Bio-composites derived from rubberwood particles were manufactured using two different configurations as a strategy to examine the potential of this species with respect to mechanical behavior. Homogeneous panels were developed from particles at the saturation condition, and heterogeneous panels were obtained from dry particles conditioned at 12% moisture content. Both examples were heat-pressed and glued with castor oil-based polyurethane resin. Density, short-term water absorption and thickness swelling, modulus of rupture and modulus of elasticity in the static bending and perpendicular tensile were evaluated. Panels derived fromrubberwood particles proved to be viable according to the technical standards.

Stress-Affected ORR on Stainless Steel

Oxygen reduction reaction (ORR) is an important cathodic reaction that often drives galvanic corrosion. In atmospheric environments, this reaction is responsible for accelerated corrosion from enhanced transport associated with discontinuous electrolytes. In load bearing structures, galvanic couples are subject to mechanical stresses that often necessitates these dissimilar metal unions. Greater understanding of mechanical stress effects on fundamental reactions of galvanic corrosion, such as ORR, is important from a forecasting perspective for improved prediction of component lifetimes and service requirements. Furthermore, extension of this behavior to confined, concentrated electrolytes is important to understand stress effects in atmospheric environments.This work reports the impact of tensile stress upon oxygen reduction reaction (ORR) for stainless steel fastener materials. Chronoamperometry was used to observe and quantify the influence of tensile stress profiles on ORR under NaCl droplet electrolytes. NaCl was utilized as a seawater proxy at concentrations of 0.6 M NaCl and 4.6 M NaCl, the latter corresponding to 80% relative humidity, which is near the deliquescence point for NaCl. The ORR current was shown to increase with tensile stress and displayed reversible behavior with simple stress profiles. Deoxygenated experiments were performed to isolate ORR contributions from oxide dynamics. Details of current transients during strain ramping are used to demonstrate these features are distinct from the ORR current shift observed during static tensile stress. Polarization experiments were performed during static tensile holds in the elastic and plastic regime for greater insight of stress effects on reduction kinetics. EIS and Mott-Schottky experiments were conducted to gain insight into the oxide behavior.

Hydrogen Embrittlement Behavior of Plastically Pre-Strained and Cathodically Hydrogen-Charged 316H Grade Austenitic Stainless Steel

In this work, the effects of electrochemical hydrogen charging of 316H grade austenitic stainless steel were investigated in order to characterize its hydrogen embrittlement (HE) resistance. The as-received 316H material was in a fully recrystallized (solution-annealed) material condition. The susceptibility to HE of the studied material was evaluated by determination of the embrittlement index from the results of conventional uniaxial tensile tests of nonhydrogenated and hydrogen-charged test specimens. The study was focused on the effects of two selected plastic pre-strain levels of tensile specimens on their resulting HE resistance. The selected pre-strains corresponded to the tensile stress conditions within the “yield stress–ultimate tensile strength” (YS–UTS) range and directly at the UTS point. The obtained embrittlement indices for the presently used pre-straining and hydrogen charging conditions indicated that the HE of the studied material states was small. However, it was revealed that the observed degradation of deformation properties of plastically pre-strained and hydrogen-charged materials was mainly caused by gradual plasticity exhaustion due to tensile straining, which well correlated with the observed effects indicated by electron backscatter diffraction analyses and indentation hardness measurements.

High-density Polyethylene - Expanded Perlite Composites: Structural Oriented Analysis of Mechanical and Thermomechanical Properties

As part of this work, research was carried out on the effect of the addition of expanded perlite (PR) on the mechanical and thermomechanical properties of high-density polyethylene (PE) composites. Composites containing from 1 to 10 wt% of the inorganic filler were produced. Polyethylene-based composites manufactured by twin-screw extrusion and formed in the compression molding process were subjected to mechanical, thermomechanical, and structural analyses. The structure of polymer composites and filler was analyzed using scanning electron microscopy (SEM). It has been correlated with the static tensile tests and results of dynamic thermomechanical analysis (DMA). As part of the work, several thermomechanical parameters were calculated, and the obtained results were discussed with the evaluation of interfacial adhesion based on microscopic analysis. The research showed that despite introducing a 10 wt% of particle-shaped filler, the composites show increased stiffness without noticeable deterioration in tensile strength, simultaneously reducing toughness and brittleness. The analysis of the thermomechanical properties showed the lack of significant effects of the filler influence on the polymer matrix.

Experimental study on the effect of grouting volume on the tensile performance of offset semi-grouted couplers

Research results have shown that the mechanical properties of sleeve grouting connections are related to the diameter of the rebar, the sleeve, the grout, the temperature and the loading method, but research on the factor of grout volume needs to be further developed. Therefore, this paper considers the effects of three grouting volumes (50%, 75% grouting and 100% full grouting) on the tensile properties of the joint under the offset condition of the rebar. A total of 22 uniaxial tensile tests on semi-grouted steel sleeve connection specimens were carried out, mainly to study the damage morphology, load-displacement relationship, stiffness and the strain change law on the surface of the rebar and the sleeve under different grouting amount, etc. The stress mechanism of the specimens in the tensile condition was analysed, and the effective bond length calculation model was proposed with reference to the steel-concrete bond strength research theory, and the formula for calculating the maximum bond stress related to the effective anchorage length was obtained. Studies have shown that the grouting amount affects the load bearing capacity and stiffness, and that the quality of the specimen joint is reliable when the grouting volume reaches more than 75% of the design grouting volume.

Reversible Stress‐Driven and Stress‐Free Two‐Way Shape Memory Effect in a Sol‐Gel Crosslinked Polycaprolactone

AbstractThe two‐way shape memory effect is the ability of a material to change its shape between two configurations upon application and removal of a stimulus, and, among shape memory polymers, it is featured only by few systems, such as semicrystalline networks. When studied under tensile conditions, it consists of elongation–contraction cycles along cooling and heating across the crystallization and melting region, typically under the application of a constant load. However, recent studies on crosslinked semicrystalline co‐polymers demonstrate that also a completely stress‐free, or self‐sustained, two‐way effect may be achieved through specific thermomechanical cycles. This effect is currently regarded with interest for the development of intrinsically reversible sensors and actuators, and it may also be displayed by simpler materials, as homopolymer‐based semicrystalline networks. Only seldom articles investigate this possibility, therefore in this work the two‐way shape memory behavior is studied on a poly(ɛ‐caprolactone) system, crosslinked by means of a sol‐gel approach. The effect is studied both under stress‐driven and stress‐free condition, by applying properly set‐up thermo‐mechanical histories. The results allow to describe the effect as a function of temperature, to reveal the dependence on specific testing parameters and to compare the extent of the reversible strain variation under these two conditions.

Three-stage breakage model for laminated glass plate under low-velocity impact

Two failure modes of laminated glass under impact loading are summarized, after which a series of experiments are carried out and a three-stage breakage model for laminated glass plate is proposed. The three-stage breakage model consists of an elastic stage (stage Ⅰ), a stage of total breakage of the back glass layer (stage Ⅱ) and a stage of total breakage of both layers of glass (stage Ⅲ). Furthermore, a combined TCK-JH2 constitutive model is proposed for the numerical analysis conducted with Finite Element Method (FEM). In this constitutive model, the TCK model is employed when the material is under tensile condition whereas the JH2 model is employed when the material is under compressive condition. Moreover, a stiffness recovery behavior is defined. The criterion of tension and compression is studied as well.

F.E.M Analysis of Static Tensile Properties of Corroded Steel Structure at Connections

F.E.M Analysis of Static Tensile Properties of Corroded Steel Structure at Connections

Numerical modeling and constitutive model verification for high-strength automotive steel

In this paper, the quasi-static and dynamic tensile tests with a gauge length of 20 mm for dual-phase (DP) 780 steel were conducted under strain rates ranging from 10−3 to 103/s. The neglected details and differences between the quasi-static and dynamic tensile test conditions were investigated to develop an accurate numerical modeling method. A high-precision combination method for the empirical constitutive model was proposed and utilized in the developed numerical model to verify the ability of the constitutive model to reproduce the experimental data at different strain rates. The excellent results indicate that the adjusted determination coefficient of the constitutive model, the adjustable range of the extrapolation curves, and the proportion factor P in the combined constitutive model are the key parameters for accurately describing the quasi-static and dynamic mechanical behavior before and after the necking.

Stress Dependence on Relaxation of Deformation Induced by Laser Spot Heating.

This paper deals with a non-destructive analysis of residual stress through the visualization of deformation behaviors induced by a local spot heating. Deformation was applied to the surface of an aluminum alloy with an infrared spot laser. The heating process is non-contact, and the applied strain is reversible in the range of room temperature to approximately +10 °C. The specimen was initially pulled up to elastic tensile stress using a tensile test machine under the assumption that the material was subject to the tensile residual stress. The relaxation behaviors of the applied strain under tensile stress conditions were evaluated using contact and non-contact methods, i.e., two strain gauges (the contact method) and a two-dimensional electronic speckle pattern interferometer (non-contact method). The results are discussed based on the stress dependencies of the thermal expansion coefficient and the elasticity of the materials.

Effect of fiber orientation on the fatigue crack initiation and propagation of glass fiber reinforced plastics

AbstractIn recent years, glass‐fiber‐reinforced plastic (GFRP) applications have expanded. This study elucidates the fatigue fracture mechanism of GFRP with different fiber orientations and experimentally clarifies the relationship between fiber orientation and fracture mechanism by using specimens with unidirectional simple fiber orientations. First, Static tensile and fatigue tests are performed on two types of specimens with fibers oriented in a single direction (parallel to the load axis and orthogonal to the load axis), and it is found that specimens with a single fiber orientation parallel to the load axis shows higher strength in both tests. Next, In the case of GFRP with fibers oriented parallel to the load axis, it is found that fatigue loading causes fatigue crack initiation at the fiber ends, followed by fiber localized debonding due to crack propagation at the fiber‐matrix interface and that the crack propagation rate gradually decreases and stops. Therefore, this suggests that the increase in fiber length of fibers oriented parallel to the load axis in GFRP leads to an increase in the crack propagation life at the fiber‐matrix interface, which leads to an increase in fatigue life.

Static and Fatigue Tensile Behavior and Damage Mechanisms Analysis in Aged Flax Fiber/PLA Composite

The aim of this paper is to analyze the effect of water aging of flax/PLA composites on their mechanical characteristics and damage mechanisms. The composites were manufactured with three-dimensional (3D) printer using bio-based material which is polylactic acid reinforced with flax fiber. The composites studied were subjected to water immersion at room temperature and tested in static and fatigue tensile tests for different immersion times. During mechanical tests, the acoustic emissions (AE) method was utilized to identify the emergence of damage processes and to track their evolution. Moreover, macroscopic and microscopic data were used to study damage processes. To confirm the reality of the damage mechanisms observed, microscopic data were linked with acoustic emission classes. Two types of events were observed by acoustic emissions associated with two composite damage mechanisms. Young’s modulus and stress decreased with aging, according to static testing. However, there was an increase in the strain. Strength and damping properties of unaged and aged composites were investigated using fatigue tensile tests. The results showed that water uptake induced a decrease in strength and stiffness and an increase in damping when compared in terms of aging time. There was also a reduction in useful life as immersion time increased.

A Multistage Analysis of Asphalt Binder Nanocrack Generation and Self-Healing Behavior Based on Molecular Dynamics.

In order to study the characteristics and laws of nanocrack generation and self-healing behavior of asphalt materials under tensile action, the molecular dynamics (MD) method was used to simulate the continuous “tensile failure—self-healing” process, and this study remedies the shortcomings of existing experimental and observational methods. It is found that the MD-reproduced formation process of asphalt binder nanocrack contains four stages: “tensile extension”, “nanocrack generation”, “crack adding, expanding and penetrating” and “cracking failure”. The influence of tensile conditions on the tensile cracking simulation of an asphalt binder model was analyzed, and it was found that low temperature and high loading rate would increase the tensile strength of the asphalt binder model. In addition, the MD-reproduced healing process of asphalt binder nanocracks can be divided into four stages: “surface approach”, “surface rearrangement”, “surface wetting” and “diffusion”, which is similar to the healing process of polymers. Finally, from the perspective of energy change, the change rule of dominant van der Waals energy in the self-healing process was studied. Based on the existing research, the influence of damage degree on the healing performance of asphalt binder and its mechanism were further analyzed. The research results further enrich the theoretical research on microlevel cracking and healing of asphalt materials, and have certain theoretical value for the further development of self-healing asphalt materials.

Multifunctional Carbon Nanotubes-Reinforced Surlyn Nanocomposites: A Study of Strain-Sensing and Self-Healing Capabilities.

Multifunctional nanocomposites based on carbon nanotubes (CNT)-reinforced Surlyn, which is a commercial ionomeric polymer, are manufactured by micro-compounding and hot-press processes. Multifunctionality is studied in terms of electromechanical response and self-healing abilities. The strain sensing analysis under tensile conditions shows ultra-high gauge factor (GF) values from 10 to 20 at low strain levels up to 106 at high strain levels, and a decreasing sensitivity as CNT content increases because of the reduction in the tunneling distance between neighboring nanoparticles. The electromechanical response under consecutive tensile cycles demonstrated the robustness of the proposed materials due to the repeatability of both responses. With regard to mechanical properties, the addition of CNT induces a clear increase in Young’s modulus because the nanoparticles enable uniform load distributions. Moreover, self-healing capabilities are improved when 4 and 5 wt.% CNT are introduced because of the synergistic effect of the high thermal conductivity of CNT and their homogeneous distribution, promoting an increase in the thermal conductivity of bulk nanocomposites. Thus, by comparing the measured functionalities, 4 and 5 wt.% CNT-reinforced Surlyn nanocomposites showed a high potential for various applications due to their high degree of multifunctionality.