Tensile Fatigue Properties Research Articles

Evaluation of tensile and low-cycle fatigue properties at elevated temperatures in piston aluminum-silicon alloys with and without nano-clay-particles and heat treatment

In this article, mechanical and low-cycle fatigue (LCF) properties of piston aluminum alloys were characterized. In addition, the effect of the reinforcement including nano-clay-particles and the heat treatment was also investigated. For this purpose, nano-particles were added to the aluminum alloy and then samples were heat-treated. Fully-reversed strain-controlled LCF tests were conducted besides tensile experiments. The strain amplitudes were set to 0.20%, 0.25%, 0.30%, 0.35%, 0.40% and 0.45% under the strain rate of 1%/s. They were repeated at four different temperatures (25 °C, 200 °C, 250 °C and 300 °C). Obtained results showed that there were no significant differences between mechanical properties such as the yield stress, the ultimate stress and the elastic modulus of specimens due to heat treat and nano-clay-particles. However, a little increment of the elongation of the heat-treated reinforced sample was observed. The reinforcement was not an effective parameter on the LCF lifetime at lower temperatures. However, the LCF lifetime of the base material decreased significantly by the reinforcement at 300 °C.

The role of microstructure and strain rate on the mechanical behavior of Ti-6Al-4V produced by powder metallurgy

Hydrogen sintering and phase transformation (HSPT), a powder metallurgy process, has been previously shown to produce desirable microstructures in Ti-6Al-4V components with corresponding excellent static and fatigue tensile properties. In the current study, three microstructures produced by HSPT and one produced by traditional wrought processing were tested under compression at strain rates of 0.001, 0.1, and > 1000 s−1. The wrought condition exhibited the best toughness at 0.001 s−1, but had the worst performance at both 0.1 and > 1000 s−1 strain rates. The HSPT condition with a globularized microstructure performed the best at 1000 s−1. From microstructural analyses, it is shown that the wrought condition had strong macroscopic texture consistent with hot rolling above the β-transus temperature. It is proposed that this macrotexture made the wrought material susceptible to relatively early-onset shear banding at all but the lowest strain rate. Being a powder metallurgical process with no mechanical working, this macrotexture does not form during the HSPT process.

Characterization of eco-friendly processing aids for styrene butadiene rubber composites with silica

With the development of environmentally friendly “green tires” in the tire industry, silica has been used as a reinforcing filler material in tread compounds. With regard to this rubber compounding process, non-toxic, and renewable processing aids are required. We fabricated such processing aids with multi-alcohol components of hydrophobic and hydrophilic groups (M-A-S) to make the hydrophilic silica compatible with the hydrophobic rubber matrix. The rubber composites with M-A-S showed remarkable enhancements in the mechanical properties, specifically the tensile strength, elongation and fatigue properties due to the improved dispersion of silica in the rubber matrix. They also exhibited outstanding heat build-up, good rebound resilience, and abrasion levels at low loadings. Furthermore, M-A-S were added directly to tread compounds to make a pneumatic tire with enhanced high-speed durability and enhanced dry and wet braking due to the strong interfacial interaction between the silica and the rubber matrix. These results demonstrate the advantages of the proposed potential replacement for metal-ion processing aids for tire engineering.

Tensile Fatigue of Poly(Vinyl Alcohol) Hydrogels with Bio‐Friendly Toughening Agents

AbstractInspired by the avoidance of toxic chemical crosslinkers and harsh reaction conditions, this work describes a poly(vinyl alcohol)‐based (PVA) double‐network (DN) hydrogel aimed at maintaining biocompatibility through the combined use of bio‐friendly additives and freezing–thawing cyclic processing for the application of synthetic soft‐polymer implants. This DN hydrogel is studied using techniques that characterize both its chemical and mechanical behavior. A variety of bio‐friendly additives are screened for their effectiveness at improving the toughness of the PVA hydrogel system in monotonic tension. Starch is selected as the best additive for further tensile testing as it brings about a near 30% increase in ultimate tensile strength and maintains ease of processing. This PVA–starch DN sample is then studied for its tensile fatigue properties through cyclic, strain‐controlled testing to develop a fatigue life curve. Though an increase in monotonic tensile strength is observed, the PVA–starch DN hydrogel does not bring about an improvement in the fatigue behavior as compared to the control. Although synthetic hydrogel reinforcement is widely researched, this work presents the first fatigue analysis of its kind and it is intended to serve as a guide for future fatigue studies of reinforced hydrogels.

Tensile and high-cycle fatigue performance of HRB500 high-strength steel rebars joined by flash butt welding

In this research, extensive testing results of the specimens of HRB500 high-strength steel rebars joined by flash butt welding were demonstrated, including metallographic and micro-hardness tests, monotonic tensile tests, high-cycle fatigue tests, and fracture surface analysis. The chief aim of the present research is to investigate the applicability of flash butt welding for HRB500 high-strength steel rebars. Thus, these tests were executed on the welded specimens, which were previously manufactured to evaluate the tensile and high-cycle fatigue properties. Meanwhile, a series of experimental technical details were proposed in the test process. Some conclusions can be obtained as follows: welding heat can change the metallographic structures of HRB500 high-strength steel rebars, and the welding heat-affected zone on the steel rebars with diameter of 16 mm is totally about 10 cm in length. Besides, the deformability and tensile strength of the welded specimens decline with their diameter degrees increasing, and brittle fractures occur in those welded specimens with diameter of 32 mm. Furthermore, three-parameter S-N curves of the welded specimens and the steel rebars base materials are obtained based on the fatigue test results. Fatigue strengths of welded specimens decrease with their diameters increasing, and reduction of high-cycle fatigue strength is more apparent for large-diameter welded specimens. Welded specimens are more prone to pre-mature fatigue failure than base materials of HRB500 high-strength steel rebars, and the rate of change in fatigue strength of welded specimen decreases with the increase of loading cycles. At last, mechanism of crack propagation in fatigue process is analyzed and further evaluated by fracture surface analysis with the aim of wider application.

Development of High Temperature Oxidation Resistant Titanium Alloy Arconic-THORTM

The aeroengine and airframe applications of titanium alloys are often limited by their insufficient oxidation resistance to the aggressive environment at higher temperatures. A high temperature oxidation resistant titanium alloy (Arconic-THORTM) has been developed. This alloy is an alpha-beta alloy with superior oxidation resistance and improved creep resistance. The oxidation weight gain of Arconic-THORTM is much lower than Ti-6242 and Beta 21s in the temperature range up to 750˚C. The room and elevated temperature properties of Arconic-THORTM are comparable to those for Ti-6242. Arconic-THORTM also shows superior, post-thermal-exposure tensile strength, ductility, and fatigue properties, and is capable of being cold formed, hot formed, and superplastic formed, welded and heat treated to different product geometries. The microstructures and mechanical properties for sheet manufactured from the production ingots are presented and discussed in this study.

Effect of toughened polyamide/carbon fiber interlace braid fabric on the mechanical performance of CFRP laminates

Delamination resistance and epoxy matrix brittle fracture have been the main issues in carbon/epoxy composites laminates. Various studies have been reported to complement the brittle fracture of epoxy matrix. Conventional methods of fabricating toughened carbon/epoxy composite laminates were thermo-plastic veils and films interleaving methods, directly toughening the matrix resin and dispersing nanoparticles in the matrix. In this study, the carbon/epoxy composites laminates were manufactured using carbon fiber/polyamide fiber braided fabrics. The chemical interactions between polyamide and epoxy matrix resin were investigated by Fourier transform infrared spectroscopy, which resulted in ring opening of the epoxide group by the amide group. The compression after impact strength and the interlaminar toughness of the carbon/epoxy composite laminate were increased by 31%, and the strain energy release rates were increased by 120% compared to the virgin interface composite. In the case of carbon/epoxy composite laminates interlaced with polyamide fibers, the mechanical properties, such as the tensile strength and fatigue properties, were improved as tensile modulus decreased.

The effect of niobium addition on the microstructure and properties of cast iron used in cylinder head

Cylinder head is one of the most important parts of heated components in the engine, while cracking due to low strength and large residual stress at high temperature is the main failure mode of cylinder head. With the growing demand of good performance and high reliability, gray cast iron with trace alloying element and optimized annealing process are probably effective ways in obtaining suitable materials. The effect of niobium addition on the microstructure and properties of cast iron used in cylinder head is studied in this paper. The results show that, the tensile strength, toughness, fatigue properties and thermal fatigue properties of gray cast iron are improved by adding trace niobium elements. The specimen with 0.20% niobium shows better comprehensive mechanical properties than others. The addition of trace niobium elements can not only refine the graphite, eutectic cell, carbide and phosphorus eutectic, but also reduce the pearlite lamellar space, thus strengthening the matrix. The cylinder head is made by cast iron with 0.20% niobium addition, and the annealing process of thermal aging is optimized. The residual stress of cylinder head can be maintained at a low level by adopting annealing process with higher holding temperature, longer holding time, lower cooling rate and lower outlet temperature. The analysis of microstructure, mechanical properties and residual stress for niobium alloyed cast iron is helpful for solving the cracking problem of cylinder head, and providing scientific basis for improving engine reliability.

Investigation on fatigue behavior and damage mechanism of C/BMI composites under hygrothermal environment

In this paper, the fatigue behavior and damage mechanism of C/BMI composites in hygrothermal environment were studied. T700/HT280 composite and its matrix resin were subjected to the hygrothermal aging treatment of 80 °C/85% RH. Moisture absorption rate, FTIR, DMA, Static tensile properties and fatigue properties of materials were tested before and after hygrothermal aging, respectively. The results show that the moisture absorption rate of composite and resin is in accordance with the Fick's second law. The maximum moisture absorption rate of composite is about 1/3 of resin's. With the increase of the hygrothermal aging time, the tensile strength of the composite increases and then decreases. The stiffness degradation curves of the original specimens at 60% and 65% stress levels follow the “fast-slow-fast” trend which presents a complete three stages of stiffness degradation. The fatigue properties damage of the materials by the hygrothermal aging can be attributed to the interface debonding and delamination between the interface and the layer under the action of moisture absorption and hygrothermal stress. The stage III of the stiffness degradation curve and the area of the hysteresis energy curve can effectively characterize the environmental damage effects induced by the hygrothermal environment factors.

Mechanical properties of the inertia friction welded aluminum/stainless steel joint

Mechanical properties of aluminum alloy/stainless steel joint including tensile strength, bending angle, impact toughness, and fatigue property were evaluated, and the effects of friction pressure and rotational speed were also discussed in this work. Results showed that the intermetallic compound (IMC) layer was formed at the bonding interface of the joint, and a thicker IMC layer was observed in the outer region of the joint, and the thickness decreased slightly in the edge region. The thickness of the IMC layer increased with increasing rotational speed. As friction pressure increased, the tensile strength of the joint gradually increased. Joint strength reached to the maximum tensile strength of 323 MPa when the rotational speed and friction pressure were 1100 rpm and 180 MPa, respectively. With the increase of friction pressure, the bending angle of the joint first increased and then decreased. The bending angle reached to 94°, and the welded joint had the excellent bending ductility. The average impact-absorbing energy of joints was 14.47 J, and the maximum fatigue cycle number of joints could reach to 1.25 × 105.

Tensile and fatigue properties of the Bridgman directionally solidified Fe-Al-Ta eutectic

Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates. High-oriented lamellar (or rod-like) Fe2Ta(Al) phase is uniformly distributed into Fe(Al,Ta) matrix. Micro-hardness, tensile and high cycle fatigue properties of the Fe-Al-Ta eutectic at different solidification rates were systematically studied. Moreover, the fracture morphologies were observed by SEM. It is found that the mechanical properties of the Fe-Al-Ta eutectic composites are better than that of the as-cast Fe-Al-Ta eutectic alloy because of the directional heat flow. Finally, the strengthening mechanism of Fe-Al-Ta eutectic was discussed.

Ribose pre-treatment can protect the fatigue life of γ-irradiation sterilized bone.

Structural bone allografts are often sterilized with γ-irradiation to decrease infection risk, which unfortunately degrades the bone collagen connectivity, making the bone weak and brittle. In previous studies, we successfully protected the quasi-static mechanical properties of human cortical bone by pre-treating with ribose, prior to irradiation. This study focused on the quasi-static and fatigue tensile properties of ribose treated irradiated sterilized bone allografts. Seventy-five samples were cut from the mid-shaft diaphysis of human femurs into standardized dog-bone shape geometries for quasi-static and fatigue tensile testing. Specimens were prepared in sets of three adjacent specimens. Each set was made of a normal (N), irradiated (I) and ribose pre-treated+irradiation (R) group. The R group was incubated in a 1.2M ribose solution before γ-irradiation. The quasi-static tensile and decalcified tests were conducted to failure under displacement control. The fatigue samples were tested under cyclic loading (10Hz, peak stress of 45MP, minimum-to-maximum stress ratio of 0.1) until failure or reaching 10 million cycles. Ribose pre-treatment significantly improved significantly the mechanical properties of irradiation sterilized human bone in the quasi-static tensile and decalcified tests. The fatigue life of the irradiated group was impaired by 99% in comparison to the normal control. Surprisingly, the R-group has significantly superior properties over the I-group and N-group (p < 0.01, p < 0.05) (> 100%). This study shows that incubating human cortical bone in a ribose solution prior to irradiation can indeed improve the fatigue life of irradiation-sterilized cortical bone allografts.

Enhancement of fatigue properties of 2024-T351 aluminum alloy processed by cryogenic laser peening

The tensile fatigue performance of 2024-T351 aluminum alloy processed by room temperature laser peening (RT-LP) and cryogenic laser peening (CLP) were explored. The nanoindentation measurement was performed. Scanning electron microscopic and transmission electron microscopic were used to inspect the microstructure evolution. Experimental results indicated that tensile fatigue life of the specimen subjected to CLP increased by 6.8% when compared with the RT-LP specimen. Additionally, CLP could induce finer grain and higher-density of dislocation structure, which have an important contribution to improving the nano-hardness and tensile fatigue properties of 2024-T351 aluminum alloy.

A Study of Crack Initiation Mechanism in the Aluminum Alloy 7475-T7351 when Tensile Loading

A study of 3D surface topography of the aluminum alloy 7475-T7351 after advanced machining and its material and mechanical properties were investigated in situ herein the scanning electron microscope TESCAN MIRA 3, equipped with a brand new combined tensile fixture MT1000 (NewTec, France). Advanced characterizations of material structures and electron backscattered diffraction mapping (EBSD) of selected chemical elements were made, as well as the energy dispersive X-ray analyses of the surface and distributions of the material inclusions. Some very thin cross-sections of the material have been produced by the focus ion beam technique also. The tensile tests confirmed that the cracks nucleated at the interfaces of brittle particles and metal material matrix. Consequently, the cracks spread under the increasing tensile loading and the samples were broken finally before reaching the standard tensile strength limits even. The fatigue results displayed an evident dispersion of the data, but the mechanism of fracture was similar. The surfaces topographies that have been made under selected cutting conditions by face milling operation have not proved to have any decisive impact on the fatigue properties. On contrary, a very evident decohesion between the alumina matrix and brittle inclusions have been observed frequently affecting the strength of the material. The main conclusion is that the phases the complex Al7Cu2Fe and Al-Cr-Fe-Cu-Si intermetallic inclusions have the crucial effect on the tensile mechanical and fatigue properties of the material, suppressing the expected effect of machining and surface topography.

Mechanical behavior of course-grain and ultrafine-grain titanium for biomedical application

The manuscript is devoted to the investigation of microstructure, static and fatigue tensile properties of commercially pure titanium grade 2 in two states with coarse grains (CG ≈ 25 µm) and ultra-fine grains (UFG ≈ 0.2 µm). During mechanical tests, the in situ monitoring was conducted by means of acoustic emission and digital image correlation. Scanning electron microscopy was employed for fracture surface observations. The results of the tensile tests show significant growth in ultimate strength and decrease of ductility due to grain-boundary strengthening. Fatigue tests revealed that the high amount of defects (grain boundaries, dislocations, etc.) in UFG suppress plastic deformation and leads to earlier crack initiation, however, at the macrocrack growth stage, these impurities are obstacles for the transgranular mechanism of fracture. The experimental data obtained allow one to get the appropriate understanding of the mechanisms responsible for the variation of mechanical properties and fracture patterns as well as to attain quantitative estimation of strain localization induced by the grain refinement.

Tensile and Fatigue Properties of Miniature Size Specimen of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge Lead-Free Solder

Tensile and low cycle fatigue properties of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge (mass%) lead-free solder were investigated using miniature size specimens and obtained data were compared to those of Sn-3.0Ag-0.5Cu (mass%). The microstructure of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge consists of dendritic β-Sn phases and ternary eutectic phases surrounding them which are composed of β-Sn, (Cu,Ni)6Sn5 and Ag3Sn. Tensile strength and 0.1% proof stress of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge are superior to those of Sn-3.0Ag-0.5Cu at 25°C and 150°C. However, elongation of it is inferior to that of Sn-3.0Ag-0.5Cu at both temperatures. Fatigue lives of both alloys obey the Manson-Coffin equation and are analogous at 25°C. Although fatigue lives of both alloys decrease at 150°C, the fatigue life of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge is inferior to that of Sn-3.0Ag-0.5Cu. At 150°C, the crack mainly progresses at grain boundaries of recrystallized grains. Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge has several grain boundaies which can be the origin of the crack so that fatigue lives degrade at 150°C.

Comparing the effects of waste engine and cooking oil on the properties of asphalt concrete containing reclaimed asphalt pavement (RAP)

The effects of using waste engine oil (WEO) and waste cooking oil (WCO) as rejuvenators on some engineering properties of asphalt concrete containing reclaimed asphalt pavement (RAP) have been studied. 10% (by the weight of total binder) of the rejuvenators has been added to asphalt concrete containing 25%, 50% and 75% (by the weight of aggregate) of RAP, and the Marshall properties, indirect tensile strength (ITS), permanent deformation and fatigue properties of the mixtures have been evaluated. The effect of rejuvenators on Marshall properties depends on RAP content and type of rejuvenator, with higher values for the mixtures containing WEO. The ITS of the mixtures increase with increasing RAP content, and decreases with increasing rejuvenators content. Addition of WEO results in lower accumulated strain in the mixtures than adding WCO. In addition, the accumulated strain in the mixtures containing 50% of RAP is higher than that in the mixtures containing 25% and 75% of RAP. The fatigue life of the mixtures was found to increase with increasing RAP content and decrease by addition of rejuvenator with a higher reduction for the WCO. In general, it is concluded that using the rejuvenators enables using higher RAP content in recycled asphaltic mixtures.

TENSILE AND HIGH CYCLE FATIGUE PROPERTIES OF ANNEALED TI6AL4V (ELI) SPECIMENS PRODUCED BY DIRECT METAL LASER SINTERING

The tensile and high cycle fatigue (HCF) properties of high temperature annealed (HTA) direct metal laser sintered (DMLS) Ti6Al4V extra low interstitial (ELI) machined and polished specimens were investigated. The HTA heat treatment of the specimens resulted in the nucleation and growth of the alpha and beta grains from the acicular ?′ martensite grains, improving their elongation to failure. The specimens were micro-CT scanned in an attempt to relate the pores in the specimens to their fatigue properties. The micro-CT pore information from suspected crack initiation pores on the surfaces of eventual fracture was used to calculate the stress intensity factors, which correlated well with the decreasing cycles to failure of the fatigue test specimens for all three build directions. Three representative specimens were analysed, and the ‘killer pore’ was identified in each micro-CT scan and fractograph, all of which were proximal to the surface of the specimen.

Fatigue performance of hydroxyapatite filled polyetheretherketone functional gradient biocomposites

ABSTRACTHydroxyapatite filled polyetheretherketone functional gradient biocomposites (HA/PEEK FGBm) is one of the most promising orthopedic implant biomaterials. In this study, The influences of the total HA content, hydroxyapatite concentration difference between adjacent layers (HCDBAL), stress level, and notch sensitivity on the tensile fatigue properties of HA/PEEK FGBm were systematically investigated. Results of fatigue-resistance tests indicated that HA/PEEK FGBm presented excellent tensile fatigue-resistance properties under different fatigue cyclic load. The tensile fatigue-resistance properties of HA/PEEK FGBm are superior to that of HA/PEEK biocomposites. The notch sensitivity has negative influence on the tensile fatigue-resistance properties of HA/PEEK FGBm. The tensile fatigue-resistance properties of the functional gradient biocomposites obviously decreased with the rise of notch sensitivity. Studies on the mechanical properties revealed that both the tensile strength and modulus of the HA/PEEK FGBm decreased after fatigue tests.

Effect of annealing treatment on microstructure and fatigue crack growth behavior of Al–Zn–Mg–Sc–Zr alloy

Al–Zn–Mg–Sc–Zr alloy samples were annealed to four different states (under-aging, peak-aging, over-aging and double-aging) and then thoroughly investigated by means of electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), tensile and fatigue crack growth rate tests to explore the influence of annealing treatment on microstructure and fatigue crack growth behavior. The results indicate that Al3(Sc,Zr) particles can effectively refine grains and enhance tensile properties and fatigue properties. After annealing treatment, the under-aged sample and double-aged sample obtained average grain sizes of 4.9473 and 4.1257 μm, and the maximum value of yield/tensile strength (561 MPa/581 MPa) was obtained in peak-aged state. In the Paris region, fatigue crack growth rate, crack deflection and bifurcation, crack blunting and inter/trans-granular propagation were discussed based on data fitting and Laird model and Griffith theory. And the results show that the under-aged sample possesses the best resistance to fatigue crack propagation and the most tortuous and bifurcated crack path. For all samples, the fatigue crack growth rate in the rupture region was inversely proportional to yield strength.