Degradation Of Tensile Properties Research Articles

Investigation on the blooming behavior of additives in nitrile butadiene rubber at elevated temperature

AbstractThe degradation of rubber performance in service environments is closely associated with the blooming behavior of additives in the rubber. This study investigates surface precipitates and changes in tensile properties of nitrile butadiene rubber (NBR) after storage at 85°C in air. The morphology, elemental composition, phase composition, and functional groups of the precipitates were analyzed by scanning electron microscopy, energy dispersion spectroscopy, X‐ray diffraction, and fourier transform infrared spectroscopy. Based on the morphology of internal rubber particles and precipitates and variations in the Zn/C mass ratio (ERZn), the reaction between zinc oxide and stearic acid in rubber under long‐term thermal environment was determined. Four stages of blooming for the mixture of zinc oxide and zinc stearate were inferred, and the impact of the blooming on the degradation of tensile properties of NBR was established. A dramatic decrease in the elongation at break (δk) of NBR was correlated with the blooming of zinc stearate and its correspondingly weakened plasticizing effect.Highlights The core‐shell structured mixture of ZnO and Zn(St)2 bloomed onto the surface of nitrile butadiene rubber. The ratio of mass percentages of Zn to C evaluated the blooming process of additives. The migration and blooming process of precipitates were divided into four stages. The decrease in elongation of the rubber was attributed to the blooming of Zn(St)2.

An experimental study into the degradation of elastic, plastic and fracture properties of a pre-corroded ductile material at elevated temperatures

Carbon steel is one of the most commonly used engineering materials. However, the mechanical properties of steel deteriorates due to exposure to harsh environments like corrosive surroundings and high temperatures. Extensive studies have been done to understand the exclusive effect of corrosion and high temperatures on tensile and fracture properties, although their combined effect has not been addressed. The present work aims to experimentally investigate this by conducting tensile and fracture tests at elevated temperatures on pre-corroded ductile steel. Pre-corroded steel was considered with corrosion levels up to 55%. Empirical relationships were established to quantify the degradation in tensile and fracture properties. An unloading compliance approach using a single specimen was utilized to determine the J-integral fracture toughness and also establish traction separation relation for mode I. The results reveal that the combined influence increases the degradation in fracture toughness, but it restricts the degradation in tensile properties.

Dually-refined grain and precipitate microstructure of ATF-FeCrAl alloy by a two-step annealing process to separate the recrystallization from precipitation

The service of ATF-FeCrAl cladding requires excellent mechanical properties, creep resistance and radiation resistance, which can be improved by microstructure refinement. Traditional thermomechanical process is difficult to refine the matrix and precipitates simultaneously due to the interaction between the precipitation and recrystallization. Here by separating the recrystallization from the precipitation process, we proposed a two-step annealing strategy to obtain both refined grain and precipitate microstructure. A warm-rolled FeCrAl alloy was firstly annealed at a high temperature for a short time to obtain an extended recovery or recrystallized microstructure without significant precipitation. Then low-temperature annealing was applied to obtain homogenous and dense nano-sized precipitates without changing the grain size. Compared to the conventional one-step annealing processes, the alloy processed by the two-step process exhibited excellent radiation-induced hardening resistance, ultrahigh tensile strength (1064.9 MPa) at room temperature with an appreciable elongation (11.7%) and best resistance to degradation in tensile properties during exposure at 800 °C. The “dually-refined” microstructure obtained by the two-step annealing exhibits good stability under ion irradiation at 320 °C. The two-step annealing strategy can provide a promising pathway to achieve microstructure refinement for other alloy systems.

About the influence of high temperature or fire testing conditions on the tensile behavior of carbon reinforced poly phenylene sulfide laminates

This study aims to investigate the thermo-mechanical coupling in carbon fibers reinforced Poly Phenylene Sulfide (PPS) laminates subjected to critical temperature conditions. In order to dissociate the physical phenomena (degradation/decomposition on the one hand and deformation/damage mechanisms on the other hand) at play in quasi-isotropic laminates (fiber-dominated mechanical behavior), homogenous and fire testing conditions (heterogenous) were considered with or without mechanical loading. X-Ray tomographic and fractographic analyses were conducted to identify the role played by porosities formation (resulting from thermally induced deformations and damages) on the structural bearing capabilities of C/PPS laminates to be used in high-temperature environments. Under high temperature conditions (homogenous temperature distribution), the retention of tensile properties is not well preserved as the axial stiffness and strength decrease of 50% and 75%, respectively. Under fire conditions (heterogenous temperature distribution), the degradation of tensile properties is more dramatic with an 80% decrease.

Durability development of lightweight and high-strength engineered cementitious composites subject to combined sulfate–chloride attack under freeze–thaw cycles

A novel lightweight high-strength engineered cementitious composite (LECC) was developed, and its mechanical property changes and the resultant durability evolution under the triple coupling factors of chloride attack, sulfate attack, and freeze–thaw cycles were studied. The results indicate that the salt solutions can accelerate the failure of LECC under freeze–thaw cycles. Salt solutions accelerated the tensile properties degradation of LECCs, and the deterioration degree was LECC-S (sulfate) > LECC-CS (chloride-sulfate) > LECC-C (chloride). The influence degree of salt solutions on mass loss was LECC-CS > LECC-C > LECC-S, while their influence on relative dynamic elastic modulus was LECC-S > LECC-CS > LECC-C. The surface spalling and internal structure destruction of LECC after salt freezing provided a favorable channel for CO2 penetration in the environment and the external sulfate–chloride environment under low temperature offered highly suitable conditions for the formation of expansive thaumasite. The combined physical and chemical attacks of sulfate promoted chloride diffusion, but chloride ion delayed sulfate’s diffusion and expansion reaction. This study more comprehensively revealed the durability development of LECC in some abominable environments and provided data support for the engineering application of LECC.

Effects of alkaline concentration and saline contents on degradation of tensile properties, microstructure and chemical characterization of glass fiber reinforced polymer (GFRP) rebars

Glass fiber reinforced polymer (GFRP) rebar has attracted widespread attention in construction industries to mitigate steel corrosion problems which significantly affect the engineering sustainability. However, GFRP tensile strength may degrade under exposure to alkaline/saline environments, and the inherent quantitative relationship between tensile strength degradation and exposure conditions is still unclear. In this study, the tensile strength retention of GFRP rebars was found to drop to 45.9%, 47.2%, 44.2%, 41.1%, 27.6%, 30.3% and 31.9% in distilled water (DW, pH = 7), seawater (SW, pH = 8.2), sodium hydroxide solutions (NaOH, pH = 11, 12 or 13), simulated normal concrete (NC, pH = 13.6) and seawater sea-sand concrete pore solutions (SSC, pH = 13.6), respectively, after 12 months of exposure at 60 °C. Both the residual tensile strength retention and activation energy in the Arrhenius equation were found to decrease with pH in a descending quadratic parabola form. The underlying degradation mechanism was then revealed by relating the macroscopic tensile strength degradation to the water/ion diffusion and fiber/matrix deterioration at the microscopic level. The pH level rather than saline ions was uncovered to be the major influence factor for GFRP degradation. The findings of this study supply engineers with a comprehensive database on GFRP tensile strength degradation, suggesting that lowering the exposure pH rather than the saline content is critical for enhancing the durability of GFRP composites.

Modelling Temperature and Strain-Rate Dependence of Recycled Aluminium Alloy AA6061

Recycling aluminium is a topic of high interest for numerous researchers to cope with the high demand for usage of its primary sources, and to overcome the environmental issues at the same time. Yet, the deformation behaviour is lacking in the literature and thedevelopment of an appropriate numerical analysis of such recycled material is also missing without this information. It is very important to understand the behaviour of the recycled aluminium alloy under various deformation condition before any application is applied. The numerical analysis data is also important for the ease of future application simulation work. Thus, the aim of the present study is to characterize the deformation behaviour of the recycled aluminium alloy under different tensile loading condition and to model a numerical analysis for the prediction of the deformation behaviour of recycled AA6061. The deformation behaviour of the recycled AA6061 was tested over two different loading speed (1.5 mm/min and 15 mm/min) and different elevated temperature (100°C –300°C). The recycled AA6061 exhibits strain-rate dependence behaviour with mild-ductile-elastoplastic behaviour within the considered loading condition. The degradation of tensile properties is quite significant, which is due to crystallinity. Based on the experimental findings, the material model MAT_098 of Simplified Johnson-Cook model, was adopted and the input parameters were characterized. The simulation results were validated against the experimental data. A good agreement between the experimental and numerical results are obtained. The outcome of numerical analysis is important to prove a strength model is still relevant to predict the deformation behaviour of such recycle material. Further, it showed that further manufacturing advancement is required on the experimental part since an anisotropic parameterare still unavailable, yet vital for consideration.

Correlation between grain size variation and hydrogen embrittlement in a cost-effective Fe40Mn40Ni10Cr10 austenitic medium entropy alloy

The effect of grain size variation (11 μm, 34 μm) on the hydrogen-induced tensile properties degradation of a Co-free cost-effective Fe40Mn40Ni10Cr10 austenitic medium entropy alloy was investigated using a slow strain rate test. Despite improving both strength and ductility with decreasing the grain size in non-charged conditions, the fine-grain alloy showed a higher relative elongation loss after electro-chemical hydrogen charging. The larger ductility loss in the fine-grain alloy was ascribed to the fast propagation rate of major intergranular cracks and the drastic strain hardening rate drop of the alloy under hydrogen charging. The Schmid factor analysis showed that the enhanced dislocation activity in the fine-grain alloy compared with coarse-grain one was responsible for rapid hydrogen transfer to the grain boundaries, fast dislocation pile-up behind the grain boundaries, and, consequently, more severe hydrogen embrittlement. The significant stress concentration near the grain boundaries and fast intergranular crack propagation were recognized to be the main reason for premature fracture in fine-grain alloy.

Effect of Different Environmental Conditions on Durabilities of Polyester- and Vinylester-Based Glass-Fiber-Reinforced Polymer Pultruded Profiles

This paper presents the results of experimental investigations on the durability of glass-fiber-reinforced polymer (GFRP) pultruded profiles made of unsaturated polyester (UP) and vinylester (VE) resins commonly used in civil engineering. The water absorption, tensile properties, and microstructures of GFRP profiles exposed to several typical accelerated aging environments (e.g., deionized water, salt water, salt fog, and combined hygrothermal cycles) for 12 months were investigated. Moreover, a sustained loading factor was included in the test to reflect the behavior of the GFRP profiles in real structures. A normalization approach based on the controlled specimens was used to assess the effectiveness and relevance of the accelerated exposure. The results indicated that the maximum moisture absorption of both UP and VE GFRP profiles was immersed in deionized water, where the masses increased by 1.03 and 0.53%, respectively, leading to the maximum degradation of tensile strength (24.03%) of UP GFRP profile immersion in deionized water after 360 days of aging. However, the tensile modulus was more sensitive to high temperatures and has the maximum degradation (47.03%) after hygrothermal cycles. Moreover, VE GFRP profiles show superior humidity and temperature endurance. Furthermore, the sustained loading exacerbated the degradation of tensile properties slightly under the same conditions. Finally, by incorporating the cumulative damage caused by the sustained loading and a time-dependent factor into a residual strength model, a revised model was proposed to describe the tensile strength loss of pultruded UP GFRP profiles.

Degradation caused by self-multiplication of damage induced by an interplay between hydrogen and the martensite transformation in a Ni–Ti superelastic alloy

ABSTRACT The role of damage in the degradation of tensile properties related to a stress-induced martensite transformation in a hydrogen-charged Ni–Ti superelastic alloy has been investigated. By damage, we mean vacancy clusters and dislocation structures induced in advance by a dynamic interplay between hydrogen and the martensite transformation. To homogenise the hydrogen concentration, the specimen was aged at room temperature after charging with a small amount of hydrogen (approximately 30 mass ppm). In this case, no fracture occurs within 2000 cycles during a cyclic tensile deformation test in the stress plateau region generated by stress-induced martensite and reverse transformations. With this hydrogen concentration, cyclic interplay between hydrogen and the martensite transformation scarcely leads to the degradation of tensile properties. Nevertheless, following cyclic martensite transformations before aging that induces pre-damage, fracture occurs after around 1000 cycles under a cyclic tensile deformation test despite the hydrogen concentration being the same. The present results clearly indicate that pre-damage induced by hydrogen affects the subsequent transformations, thereby causing the self-multiplication of damage, which degrades the tensile properties.

Experimental investigation on mechanical performance of carbon fiber reinforced polymer wire after exposure to elevated temperature

The current study experimentally investigated the influence of elevated-temperature exposure on the mechanical performance of carbon fiber reinforced polymer (CFRP) wires through conducting the axial tensile, three-point bending and transverse load tests. The results show that the CFRP wires under axial tensile load exhibited a brittle fracture after exposure to 30 and 100 °C, and the wires after 200 °C exposure were pulled out from the anchorage. The axial tensile and three-point bending performance of the wires were adversely affected by the elevated temperature; and with the increase of the exposed temperature, the maximum contact force, maximum wire tension, maximum wire tension increment, deflection at fracture and the energy dissipation capacity of the preloaded CFRP wires in the transverse load tests declined. Based on the experimental results, reduction functions were established to quantify the degradation in tensile properties of the CFRP wires after elevated-temperature exposure, and the formulas used for predicting the post-elevated temperature transverse failure responses of the preloaded CFRP wires were proposed. Furthermore, through verification by the test results, the previously established failure criteria are demonstrated to be applicable to assess the failure state of a CFRP wire after evaluated-temperature exposure when subjected to combined tension and bending.

Study on aging properties and degradation mechanism of FRP bars

The tensile properties of fiber-reinforced composites (FRP) under various factors of composite aging were studied by tensile test. The test parameters mainly include temperature, salt spray, ultraviolet, rainwater, and stress. The results show that the higher the temperature, the faster the FRP tensile strength decreases; At the same temperature, the ultraviolet radiation has little effect on BFRP bars. Salt spray and rainwater hydrolyze the resin on the surface of the steel bars and expose the inner steel bars. Stress can accelerate the degradation of tensile properties of FRP bars. It has little effect on the elastic modulus of FRP bars. A scanning electron microscope (SEM) was used to observe the changes of steel bars and the mechanism of mechanical property degradation was studied

Carbon effect on hydrogen diffusivity and embrittlement in austenitic stainless steels

Hydrogen embrittlement behavior of three austenitic stainless steels with 0.1−0.3 wt.%C was investigated. Carbon alleviated hydrogen-induced degradation of tensile properties. Increasing the carbon content over 0.1 wt.% hardly influenced hydrogen diffusivity. Hydrogen caused cracks to initiate at grain boundaries on the sample surface, and to propagate inside the grains through α’ and ε martensites. The crack propagation was suspended by confronting a grain boundary, and did not reach the depth of hydrogen penetration. It was suggested that the carbon at grain boundaries delayed the crack initiation, and the carbon in solid solution enhanced austenite stability, which impeded the crack propagation.

AMB2018-03: Benchmark Physical Property Measurements for Material Extrusion Additive Manufacturing of Polycarbonate.

Material extrusion (MatEx) is finding increasing applications in additive manufacturing of thermoplastics due to the ease of use and the ability to process disparate polymers. Since part strength is anisotropic and frequently deviates negatively with respect to parts produced by injection molding, an urgent challenge is to predict final properties of parts made through this method. A nascent effort is underway to develop theoretical and computational models of MatEx part properties, but these efforts require comprehensive experimental data for guidance and validation. As part of the AM-Bench framework, we provide here a thorough set of measurements on a model system: polycarbonate printed in a simple rectangular shape. For the precursor material (as-received filament), we perform rheology, gel permeation chromatography, and dynamical mechanical analysis, to ascertain critical material parameters such as molar mass distribution, glass transition, and shear thinning. Following processing, we conduct X-ray computed tomography, scanning electron microscopy, depth sensing indentation, and atomic force microscopy modulus mapping. These measurements provide information related to pores, method of failure, and local modulus variations. Finally, we conduct tensile testing to assess strength and degree of anisotropy of mechanical properties. We find several effects that lead to degradation of tensile properties including the presence of pore networks, poor interfacial bonding, variations in interfacial mechanical behavior between rasters, and variable interaction of the neighboring builds within the melt state. The results provide insight into the processing-structure-property relationships and should serve as benchmarks for the development of mechanical models.

Marked Degradation of Tensile Properties Induced by Plastic Deformation after Interactions between Strain-Induced Martensite Transformation and Hydrogen for Type 316L Stainless Steel

Marked degradation of tensile properties induced by plastic deformation after dynamic interactions between strain-induced martensite transformation and hydrogen has been investigated for type 316L stainless steel by hydrogen thermal desorption analysis. Upon modified hydrogen charging reported previously, the amount of hydrogen desorbed in the low temperature range increases; the degradation of tensile properties induced by interactions between plastic deformation and hydrogen at 25 °C or induced by interactions between martensite transformation and hydrogen at −196 °C occurs even for the stainless steel with high resistance to hydrogen embrittlement. The hydrogen thermal desorption behavior is changed by each interaction, suggesting changes in hydrogen states. For specimen fractured at 25 °C, the facet-like morphology and transgranular fracture are observed on the outer part of the fracture surface. At −196 °C, a quasi-cleave fracture is observed at the initiation area. Modified hydrogen charging significantly interacts both plastic deformation and martensite transformation, eventually enhancing the degradation of tensile properties. Upon plastic deformation at 25° C after the interactions between martensite transformation and hydrogen by straining to 0.2 at −196 °C, cracks nucleate in association with martensite formed by the interactions at −196 °C and marked degradation of tensile properties occurs. It is likely that the interactions between martensite transformation and hydrogen induce damage directly related to the degradation, thereby affecting subsequent deformation. Upon dehydrogenation after the interactions between the martensite transformation and hydrogen, no degradation of tensile properties is observed. The damage induced by the interactions between martensite transformation and hydrogen probably changes to harmless defects during dehydrogenation.

Tensile Properties Degradation of Thermally Aged NR/EPDM Blend and Nanocomposites for Engine Mounting

Tensile Properties Degradation of Thermally Aged NR/EPDM Blend and Nanocomposites for Engine Mounting

Nitrogen effect on hydrogen diffusivity and hydrogen embrittlement behavior in austenitic stainless steels

Hydrogen embrittlement behavior of three austenitic stainless steels with 0.1–0.3 wt% N was investigated by electro-chemical charging of hydrogen. The degradation of tensile properties was alleviated by nitrogen. Hydrogen permeation testing revealed that the increase of nitrogen content decreased the hydrogen diffusivity, and thereby, reduced the depth of hydrogen-affected zones. Intergranular cracks were formed in an early stage of deformation by hydrogen charging and reduced the strain-hardening rate. The cracks propagated further into the grains along martensite/austenite interfaces especially in steels with less nitrogen.

CFRP Reclamation and Remanufacturing Based on a Closed-loop Recycling Process for Carbon Fibers Using Supercritical N-butanol

This study presents a closed-loop recycling process for carbon fibers using supercritical n-butanol. In the reclamation process, to achieve the highest composite recovery efficiency, the degradation of the carbon fiber-reinforced epoxy resin composites was conducted at various experimental feedstock ratios (ratio of composite waste to n-butanol), then the reclaimed carbon fiber (RCF) was characterized using various methods to develop an understanding of the changes in the properties and morphologies. In the remanufacturing process, in order to evaluate the reusability of the RCFs and the feasibility of the closed-loop recycling process for carbon fibers, the RCFs were mixed with new epoxy resin and polypropylene to remanufacture the composites, and then the mechanical properties of remanufacture composites were tested. The results show that, under an optimized process, the maximum recovery efficiency (feedstock ratio) of the composite was 0.1 g/ml. The impact of reclamation process on RCF lies in the degradation of tensile properties and the removal of sizing agent, which leads the change of the interfacial bonding strength between RCF and new resin, and eventually results in an impact on the performance of remanufacture composites. Compared with the virgin carbon fiber-reinforced composites, the improvement in the RCF-reinforced polypropylene properties and insubstantial variations in the tensile properties of the RCF validate the potential of the closed-loop recycling process for carbon fibers.

Gaseous hydrogen embrittlement of a Ni-free austenitic stainless steel containing 1 mass% nitrogen: Effects of nitrogen-enhanced dislocation planarity

We investigated the effect of hydrogen on degradation of tensile properties in a Fe–25Cr–1N austenitic stainless steel. Hydrogen was introduced by exposure to a hydrogen gas atmosphere at 100 MPa and 270 °C. Hydrogen charging caused significant ductility loss associated with nitrogen-enhanced dislocation planarity. Specifically, even without hydrogen, the nitrogen-enhanced planar dislocation glide induced micro-stress concentration, which assisted the occurrence of hydrogen-induced intergranular and quasi-cleavage fractures. The hydrogen-assisted intergranular cracking occurred along boundaries of grains where primary slip was predominantly activated. On the other hand, the hydrogen-assisted quasi-cleavage fracture took place when multiple slip systems were activated. The hydrogen-related cracks emerged, but their growth was arrested via crack blunting associated with a significant plastic deformation. Instead, new cracks formed near the crack tips. Therefore, hydrogen-assisted crack propagation occurred through repetition of crack blunting, initiation, and coalescence.

Mechanical, thermal, electrical and crystallographic behaviour of EPDM rubber/clay nanocomposites for out-door insulation applications

ABSTRACTIn this study, the degradation of tensile properties is investigated by placing the neat ethylene propylene diene monomer (EPDM) rubber and different weight percentages (2 wt%, 4 wt% and 6 wt%) of MMT clay dispersed in the EPDM rubber samples in a humidity chamber for 0, 5, 7, 12 and 14 days. The thermal properties of neat EPDM rubber and its clay nanocomposites were studied by using different instruments, namely dynamic mechanical analyser (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The viscoelastic properties are studied over the temperature range of −80°C to 80°C at different frequencies by using DMA. An increase in storage modulus and the decrease in loss tangent values are observed with the increase in clay content from 0 wt% to 6 wt% in EPDM rubber. Increase in storage modulus and glass transition temperature (Tg) values is observed with the increase in frequency from 1 Hz to 50 Hz. Also, the thermal stability and change in mass of these materials as a function of temperature and time are studied using TGA. It is found that EPDM/4 wt% clay composites exhibit the highest residual weight at 690°C while neat EPDM exhibits the highest weight loss compared to samples dispersed with other clay weight percentages. Using X-ray diffraction (XRD), 2θ value was measured and the crystal structure is investigated. Fourier transformed infrared spectroscopy (FTIR) was used to characterise the grafting of clay in the EPDM rubber. The dielectric constant and conductivity were studied for different frequencies and temperatures.