Decrease In Fatigue Life Research Articles

Asphalt Mixtures Fatigue Life Considering Various Environmental Impacts.

The pavement structure during the colder seasons (winter) or in regions located above sea level is commonly affected and deteriorated by many environmental factors. Two prominent factors are water and frost (weather) or road salt (maintenance). According to the article's literature review, there are only a few studies related to water and frost or road salt impact on mineral asphalt mixes considering fatigue. Most of the tests were performed on mixes containing common road asphalt or only one binder content level was investigated. There are no articles that investigate this problem comprehensively including new asphalt, its content levels, or production technology. Based on the literature review, the main problem regarding degradation impact on mixtures fatigue life was stated. The investigation was performed using two proprietary experimental methods allowing approximates in situ conditions regarding environmental impacts. A dynamic four-point bending fatigue test was applied to evaluate degradation considering fatigue. The investigation was performed using four coarse-graded asphalt mixtures (asphalt concrete AC 22) which differed in binder type (35/50 WMA, 35/50, 25/55-60, and 25/55-80 HIMA), content level (4.24%, 4.03%, 3.82%), and production technology (hot and warm). Regarding the results obtained, the authors proposed a degradation ratio regarding fatigue life variability. Based on the obtained results and ratio used, it was found that both interactions caused a significant fatigue life decrease-in the worst case, over tens of percent. Furthermore, it was found that asphalt mixture resistance to environmental factors depends on binder type, its content level, air void content, and discussed impact. Moreover, asphalt mixtures' susceptibility to degradation (fatigue) is extreme at lower binder content levels and accelerates due to air void content increase. In the article, it was also stated that the highest resistance was reached by a mixture with highly modified asphalt (25/55-80 HIMA). It was also found that the SBS polymer dosage increase in the asphalt matrix enhances asphalt mixture resistance to environmental impacts. The least resistant to the environmental degradation mixture was WMA (35/50 WMA).

Effects of interface cracks on reliability of surface mount technology interconnection in service environment

PurposeSurface mount technology (SMT) is widely used and plays an important role in electronic equipment. The purpose of this paper is to reveal the effects of interface cracks on the fatigue life of SMT solder joint under service load and to provide some valuable reference information for improving service reliability of SMT packages.Design/methodology/approachA 3D geometric model of SMT package is established. The mechanical properties of SMT solder joint under thermal cycling load and random vibration load were solved by 3D finite element analysis. The fatigue life of SMT solder joint under different loads can be calculated by using the modified Coffin–Manson model and high-cycle fatigue model.FindingsThe results revealed that cracks at different locations and propagation directions have different effect on the fatigue life of the SMT solder joint. From the location of the cracks, Crack 1 has the most significant impact on the thermal fatigue life of the solder joint. Under the same thermal cycling conditions, its life has decreased by 46.98%, followed by Crack 2, Crack 4 and Crack 3. On the other hand, under the same random vibration load, Crack 4 has the most significant impact on the solder joint fatigue life, reducing its life by 81.39%, followed by Crack 1, Crack 3 and Crack 2. From the crack propagation direction, with the increase of crack depth, the thermal fatigue life of the SMT solder joint decreases sharply at first and then continues to decline almost linearly. The random vibration fatigue life of the solder joint decreases continuously with the increase of crack depth. From the crack depth of 0.01 mm to 0.05 mm, the random vibration fatigue life decreases by 86.75%. When the crack width increases, the thermal and random vibration fatigue life of the solder joint decreases almost linearly.Originality/valueThis paper investigates the effects of interface cracks on the fatigue life and provides useful information on the reliability of SMT packages.

Effect of Boron on Mechanical Properties and Fatigue Life of Spring Steel for Automobile Suspension

Three Si-killed 55SiCrA suspension spring steels with different boron contents (0, 23 ppm and 43 ppm) were obtained by vacuum induction levitation melting furnace. Through hot tensile, torsional Bauschinger and rotating bending fatigue tests, the microstructure, precipitate, tensile strength, percentage of area reduction, elastic sag resistance and fatigue life of spring steel were analyzed, respectively. Boron accelerated the dynamic recrystallization at 800 ºC and prevented the formation of reticular proeutectoid ferrite and coarse pearlite in steel, then made the tempered troostite of heat-treated spring steel become fine and uniform. However, much BN and boron carbide formed along prior austenite grain boundaries in spring steel containing 43 ppm boron and was retained after quenching and tempering, leading to the decrease of ductility and fatigue life of spring steel. Therefore, 23 ppm boron was the best content for increasing hot ductility and ductility at room temperature of spring steel, and improved its tensile strength and elastic sag resistance, finally, the fatigue life increased from 5.3 × 107 cycles to 8.2 × 107 cycles.

Effect of chemical ageing on fatigue life of short glass fiber-reinforced Polyamide 6,6

In this study, the effect of hydrolysis and oxidation on fatigue life of Polyamide 6,6 reinforced with 30 wt% glass fibers has been studied systematically for the first time. The chemical changes due to these two chemical processes were monitored, especially the molar mass decrease over ageing time, homogeneous throughout the sample for hydrolysis and localized in a near-surface layer for oxidized samples. In both cases the fatigue life was significantly decreased with ageing. For homogeneously aged samples, the maximal applied stress at a given number of cycles to failure was correlated to the decrease of the molar mass of the matrix using a Flory-based model. This leads to the definition of a critical molar mass around 13 kg/mol which can be linked to the molar mass between entanglements, suggesting that fatigue is governed by fracture occurring in the glassy amorphous phase. To explain the decrease in fatigue life for oxidized heterogeneous samples, we proposed that a brittle layer, smaller than the oxidized layer itself, is considered as not sustaining any stress. The existence of this brittle layer was confirmed by fracture surface analysis and found in good agreement with the values extracted from the analytical model proposed.

ANALISIS STRUKTUR PADA DISC BRAKE DENGAN VARIASI MATERIAL DAN JUMLAH LUBANG VENTILASI TERHADAP TEMPERATUR DAN TEGANGAN EKUIVALEN

Manny disc brake are produced at conventional machinery workshop. But, the optimum value of disc brake based on heat dissipation, and the safety is unknown. One of the causes of vehicle accidents is the vehicle factor (brake failure). Prolonged and continuous braking on the disc brake can result in fadding. Continuous stress generation can decrease fatigue life. The required material and the right number of holes are needed to solve this problem. The Purpose of this research is to get the optimum temperature and stress value. In this study, simulations were carried out with CAE software on disc brakes with materials Al 7075- T6, SS 304, gray cast iron and the number of ventilation holes 36, 48, 60. The results show that the disc brake with Al 7075-T6 material and 60 ventilaton holes has the best heat dissipation with 38,005ᴼC temperature value. Material gray cast iron with number of ventilation holes 48 produces the lower equivalent stress with 89,272 Mpa. From the research it can be concluded, disc brake with higher density,has higher temperature too. The greater tensile strength of disc brake material, resulting the lower equivalent stress. The gray cast iron material and the number of ventilation holes 48 is the most optimal in temperature absorption, the longest fatigue life, and the highest fatigue safety factor, with a temperature value of 54.99ᴼC, a fatigue life of 100000000 cycles, and an FOS of 3.34.The more number of ventilation holes, has the lower of temperature result but the higher stress concentration.

Friction and Wear Behavior between Crane Wire Rope and Pulley under Different Contact Loads

Surface wear caused by contact between crane wire rope and a pulley seriously affects the mechanical properties of the wire rope. In this study, the tribological behavior of wire rope was investigated using a homemade rope–pulley sliding friction test rig. Then, the influence of different surface wear on the bending fatigue life of the rope samples was analyzed. The results show that the friction coefficient (COF) decreases with the increasing sliding distance. It reaches a minimum of approximately 0.52 when the contact load is 700 N. The surface temperature of the wire rope rises rapidly and then gradually stabilizes. The maximum temperature rise fluctuates in the range of 50 °C to 60 °C with increasing contact load. The wear scar of the wire rope is irregular, and the maximum wear width increases from approximately 1.94 mm to 2.45 mm with the contact load. Additionally, increased contact load leads to smoother wear surface of wire rope, and the wear mechanisms are mainly abrasive wear and adhesive wear. Additionally, surface wear leads to a decrease in the bending fatigue life of wire ropes, and degradation of anti-bending fatigue is more serious under a larger sliding contact load.

On the Difference in Mechanical Behavior of Glass Bead-Filled Polyamide 12 Specimens Produced by Laser Sintering and Injection Molding.

An increasing demand for additively manufactured polymer composites with optimized mechanical properties is manifesting in different industries such as aerospace, biomedical, and automotive. Laser sintering (LS) is an additive manufacturing method that has the potential to produce reinforced polymers, which can meet the stringent requirements of these industries. For the development of a commercially viable LS nylon-based composite material, previous research studies worldwide have focused on adding glass beads to the powder material with the goal to produce fully dense parts with properties more representative of injection molded (IM) thermoplastic composites. This led to the development of a commercially available glass bead-filled polyamide 12 (PA12) powder. Although this powder has been on the market for quite a while, an in-depth comparison of the mechanical behavior of laser sintered versus IM glass bead-filled PA12 is lacking. In this study, laser-sintered glass bead-filled PA12 samples were built in different orientations and compared to IM counterparts. After sample production, the mechanical performance of the produced LS and IM parts was tested and compared to evaluate the quasistatic and dynamic mechanical performance and failure mechanisms at different load levels. In addition, the glass bead-filled PA12 properties were also compared to those of standard (unfilled) LS PA12 to assess whether glass beads actually improve the mechanical performance and fatigue lifetime of the final LS samples, as suggested in literature. Results in this work present and explain the increased stiffness but decreased fatigue life of glass bead-filled polyamide parts made by LS and IM. This research can be regarded as a "benchmark" study, in which samples produced from commercially available, filled and unfilled, PA12 powder grades are compared for both LS and conventional production techniques.

Retardation effect on sheet steel under a mixed I–II mode overload revealed by experiment, DIC and FEM methods

As a high strength and commercial steel, Q420 is widely employed in many engineering applications. In this paper, a series of experiments was conducted to investigate the fatigue crack growth retardation mechanisms under mixed I–II mode overloads with loading angles 0, 30, 60 and 90°. The baseline of loading spectrum is a pure mode I cyclic loading with a mixed overload applied after pre-cracking. The results show that the crack path is always straight for each case. Both the retardation level and fatigue life decrease with the increasing loading angle. A combined model that considers the residual stress, plasticity-induced and roughness-induced crack closure effects was proposed to predict the fatigue crack growth rate and fatigue life. The predicted results agree well with several experimental results.

Effect of hydrogen on low-cycle fatigue behavior of HRB400 steel under asymmetric cyclic loading

This paper focuses on the study of ductility changes, ratcheting, and low-cycle fatigue behavior of materials after hydrogen charging. Hot-rolled ribbed bar 400 (HRB400) steel was electrochemically charged with H2SO4 solution, and the samples subjected to different hydrogen charging times were subjected to quasi-static tensile and low-cycle fatigue tests under asymmetric cyclic loading. The tests indicated that hydrogen charging changed the initial yield stress of the material, but the ultimate strength remained almost unchanged; hydrogen charging significantly changed the cyclic hysteresis behavior of the material, which increased the elastic range of the stable hysteresis curve; hydrogen charging changed the pattern of ratcheting deformation. The pattern of ratcheting deformation in the later stage was very different from that of the sample without hydrogen charging; hydrogen charging reduced the ductility of the material and resulted in a significant decrease in fatigue life. The fracturing of the hydrogen-charged samples exhibited apparent quasi-cleavage and intergranular fracture characteristics. The non-hydrogen-charged samples had two failure modes (fatigue failure and increased ratcheting deformation resulting in necking instability), whereas the hydrogen-charged samples had only one failure mode of fatigue failure. Based on the experimental analysis, a fatigue life equation that simultaneously considers the effect of hydrogen embrittlement index, mean stress, and stress amplitude is proposed. The equation was used to predict the low-cycle fatigue life of hydrogen-charged specimens under asymmetric cyclic loading, and the error between the results and the measured values was in the two-factor band.

Fatigue damage analysis of pavements under autonomous truck tire passes

Abstract Two different tire configurations consisting of a dual tire and a super single wide tire having different range and distribution of contact pressures have been analyzed. Along with the effect of speed on development of pavement damage at speeds of 5, 50 and 80 km h−1 under zero and uniform wander modes. Results show that at super slow speeds of 5 km h−1, at dual wheel moving at zero wander mode, decrease in fatigue life of the pavement is 3.5 years, which is 1.45 times more than the dual wheel moving at uniform wander and 3.4 times more than wide tire moving at uniform wander mode. The difference between fatigue damage at different lateral wander modes is prominent at speeds greater than 50 km h−1. A wide tire performs better than the dual wheel under zero wander configurations.

Model and experimental studies on the effects of load characteristics and polyurethane densities on fatigue damage of rigid polyurethane grouting materials

This work aims to theoretically and experimentally investigate the fatigue damage evolution characteristics for rigid polyurethane grouting materials (RPGM). From the theoretical perspective, based on the integral method and classic Chaboche damage evolution model, a theoretical fatigue damage model considering load characteristics (load speed and magnitude) was established. From the experimental perspective, based on the three-point bending experimental fitting, the effects of polyurethane densities on fatigue damage characteristics were considered. In this case, the damage evolution model of semi-empirical and semi-theoretical for RPGM was established. The results show that the fatigue life of RPGM decreases with the increase of load magnitude and polyurethane density but increases with the increase of load speed. On the contrary, the fatigue damage of RPGM increases with the increase of load magnitude and polyurethane density but decreases with the increase of load speed. In addition, the mean relative error between predicted values and experimental results is less than 10 %. At last, the sensitivity analysis shows that the influences of density, load magnitude, and load speed on fatigue life decrease in turn. The damage evolution model established in this work can well predict the damage behavior of RPGM in the entire life cycle. It also can provide good theoretical guidance for the design of rehabilitation and reinforcement engineering.

The Effect of Temperature and Phase Shift on the Thermomechanical Fatigue of Nickel-Based Superalloy

In this paper, the minimum temperature and phase shift effects on the thermo–mechanical fatigue (TMF) behavior of Inconel 713LC are investigated. TMF tests were performed under 0° (in-phase-IP) and +180° (out-of-phase-OP) phase shifts between mechanical strain and temperature. Cylindrical specimens were cycled at constant mechanical strain amplitude with a strain ratio of Rε = −1. Tests were performed with temperature ranges of 300–900 °C and 500–900 °C. The heating and cooling rate was 5 °C/s. Fatigue hardening/softening curves and fatigue life data were assessed. Results show that out-of-phase loading was less damaging than in-phase loading. Scanning electron microscopy (SEM) examination of metallographic sections indicated that the life-reducing damage mechanism was intergranular cavitation under in-phase loading. Transmission electron microscopy (TEM) revealed honeycomb structures for IP loading. The plastic strain localization into persistent slip bands was typical for OP loading. For out-of-phase loading, fatigue damage appeared to be dominant. The increase in the temperature range led to a significant decrease in fatigue life. The reduction of fatigue life was far more pronounced for out-of-phase loading. This can be ascribed to the accelerated crack propagation at high tensile stress under out-of-phase loading as well as the amount of accommodated plastic strain deformation. Based on the SEM scrutiny of metallographic sections and TEM observations of dislocation arrangement, the prevailing damage mechanisms were documented and the lifetime behavior was accordingly discussed.

Effect of high-low frequency superimposed loading on the fatigue crack propagation of longi-web connection joint

The superposition of low-frequency (LF) wave loads and high-frequency (HF) loads resulting from springing and whipping will cause coupling damage due to the interaction of various frequency load components. In this study, a series of fatigue tests under different high-low frequency superimposed loading (called ‘‘superimposed loading’’ hereafter) conditions were carried out, and the co-simulation of FRANC3D and ABAQUS was utilized to explore the influence of high-low frequency coupling damage on the fatigue life and crack propagation characteristics of the typical welded joint of hull structures. The results indicated that the coupling damage has a significant influence on the decrease of fatigue life, especially on the crack propagation life. In parallel, the intermittent HF loads could also lead to fatigue life reduction and should be paid attention to. Moreover, based on the simulation, a correction coefficient of effective stress intensity factor considering the influence of coupling damage was proposed.

Corrosion fatigue of Ti‐6Al‐4V coupons manufactured by directed energy deposition

AbstractTitanium is a versatile biocompatible metal that is desirable in additively manufactured medical implant devices. However, additively manufactured parts have particular microstructures, porosity, residual stress, and surface conditions which can have a strong impact on fatigue performance. Implants have an added complexity from the saline operating environment and the associated impact on the safe design life. Equally, direct energy deposition induces a complex thermal history which, if not carefully controlled, can significantly alter the mechanical/material properties of the component. This study investigates the decrease in fatigue life, in an in vitro body fluid simulation using Ringer's solution, observed in Ti‐6Al‐4V specimens extracted from coupons manufactured by directed energy deposition. An interrupted deposition strategy was employed to control build regularity, which appeared to influence certain mechanical properties, including corrosion fatigue life. An ≈50% decrease in fatigue life was observed in Ringer's solution at 6 Hz loading frequency, clearly important in designing implants.

Dynamic adhesion of polyamide 6,6 cord/rubber composites in H-pull tests: Fatigue evolution, life prediction and methodology evaluation

The influence of fatigue on adhesion of cord/rubber composites was investigated through H-pull tests. Fatigue was found to promote sulfur diffusion from rubber to RFL and induce modulus homogenizing. Higher frequency caused decrease in fatigue life due to self-heating, but the effect was negligible under low displacement amplitude. Longer fatigue life was achieved at higher R ratio, but an exceptional increase in fatigue life was found at the highest R ratio. A universal CLD model was established for predicting fatigue life. Results of model verification revealed a critical R ratio, above which H-pull test no longer accurately evaluated dynamic adhesion.

Dependence of Creep Strain and Fatigue Behavior on Surface Characteristics of Resistive Strain Gauges.

Creep behavior and fatigue life are important performance indexes that affect the long-term stability of resistive strain gauges. The resistive strain gauges, fabricated with wet etching and resistance trimming, present micro-morphology such as textures and uneven edges on the surface and side-wall profile of sensitive grids. This paper observed the micro-morphology of the sensitive grids by microscope and analyzed its range of geometric dimensions. A sine function was used to establish equivalent geometric models for the surface textures and side-wall profile. Based on time hardening theory and the S–N curve, the dependence of micro-morphology of metal resistive strain gauges on creep behavior and fatigue life was studied. The results indicate that the roughness of micro-morphology has an influence on creep behavior and fatigue life. The surface textures and side-wall profile lead to the increase of creep strain and the decrease of fatigue life in varying degrees. When 60% of the ultimate stress of the strain gauges is loaded, the average creep strain in steady-state calculated by the maximum roughness of the side-wall profile reaches up to 6.95 times that of the perfect flat surface. Under the condition of loading 70% of the ultimate stress and the same roughness, the fatigue life led by side-wall profile could be reduced to 1/25 of the textured surface. The obtained achievements promote an understanding for optimizing the fabrication process of resistive strain gauges as well as developing high-precision and long-life force sensors.

The High-cycle Fatigue Life of Cortical Bone Allografts Is Radiation Sterilization Dose-dependent: An In Vitro Study.

Structural cortical bone allografts are a reasonable treatment option for patients with large cortical bone defects caused by trauma, tumors, or complications of arthroplasty. Although structural cortical bone allografts provide the benefit of an osteoconductive material, they are susceptible to fatigue failure (fracture) and carry a risk of disease transmission. Radiation-sterilization at the recommended dose of 25 kGy decreases the risk of disease transmission. However, previous studies demonstrated that radiation sterilization at this dose can negatively impact the high cycle-fatigue life of cortical bone. Although the effects of higher doses of radiation on cortical bone allografts are well described, the effects of lower doses of radiation on a high-cycle fatigue life of cortical bone are poorly understood. (1) Does the cycle-fatigue life of human cortical allograft bone vary with gamma radiation dose levels of 0 (control), 10 kGy, 17.5 kGy, and 25 kGy? (2) What differences in Raman spectral biomarkers are observed following varying doses of gamma radiation exposure? The high-cycle fatigue behavior of human cortical bone specimens was examined at different radiation sterilization doses under physiologic stress levels (35 MPa) and in a 37° C phosphate-buffered saline bath using a custom-designed rotating-bending fatigue device. Six human femora from three donors were obtained for this study (two male, 63 and 61 years old, respectively, and one female, 48 years old). Test specimens were allocated among four treatment groups (0 kGy [control], 10 kGy, 17.5 kGy, and 25 kGy) based on donor and anatomic location of harvest site (both length and cross-sectional quadrant of femoral diaphysis) to ensure equal variation (n = 13 per group). Specimens underwent high-cycle fatigue testing to failure. The number of cycles to failure was recorded. Raman spectroscopy (a noninvasive vibrational spectroscopy used to qualitatively assess bone quality) was used to detect whether any changes in Raman spectral biomarkers occurred after varying doses of gamma radiation exposure. There was a decrease in the log-transformed mean high-cycle fatigue life in specimens irradiated at 25 kGy (5.39 ± 0.32) compared with all other groups (0 kGy: 6.20 ± 0.50; 10k Gy: 6.35 ± 0.79; 17.5 kGy: 6.01 ± 0.53; p = 0.001). Specimens irradiated at 25 kGy were also more likely to exhibit a more brittle fracture surface pattern than specimens with more ductile fracture surface patterns irradiated at 0 kGy, 10 kGy, and 17.5 kGy (p = 0.04). The Raman biomarker for the ratio of the relative amount of disordered collagen to ordered collagen showed a decrease at the 10 kGy radiation level from 1.522 ± 0.025 preirradiation to 1.489 ± 0.024 postirradiation (p = 0.01); no other detectable changes in Raman biomarkers were observed. The high-cycle fatigue life of cortical bone undergoes a nonlinear, dose-dependent decrease with an increase in gamma radiation sterilization in a clinically relevant dose range (0-25 kGy). Importantly, a notable drop-off in the high-cycle fatigue life of cortical bone appeared to occur between 17.5 kGy and 25 kGy, correlating to a sixfold decrease in mean cycles to failure. We speculate that the decrease in the Raman biomarker for disordered collagen at 10 kGy with no loss in high-cycle fatigue life may be caused by an increased amount of nonenzymatic crosslinking of the collagen backbone relative to collagen chain-scission (whereas the benefits of crosslinking may be outweighed by excess scission of the collagen backbone at higher radiation doses), but future studies will need to ascertain whether this in fact is the case. Radiation sterilization at the industry standard of 25 kGy has a substantial negative impact on the high-cycle fatigue life of cortical bone. Given these findings, it is possible to provide a meaningful increase in the high-cycle fatigue life and improve the overall functional lifetime of cortical bone allografts by lowering the radiation-sterilization dose below 25 kGy. Future work on radiation-sterilization methods at these clinically relevant doses is warranted to aid in preserving the high cycle fatigue life of cortical bone allografts while maintaining sterility.

Isothermal high-temperature fatigue behaviour of a near-γ titanium aluminide alloy

AbstractThe high-temperature fatigue behaviour of smooth cylindrical specimens of a near-γ-TiAl alloy with duplex microstructure was studied performing total-strain-controlled low-cycle-fatigue tests in the temperature range 500 – 750 °C. The tests were run in air and high vacuum. Mean stress, environmental degradation (oxygen- and hydrogen-induced embrittlement) and plastic strain range were identified to be the most significant parameters affecting damage evolution. The cyclic stress– strain response was found to depend strongly and characteristically on temperature. Below the brittle-to-ductile-transition temperature (TBD) of about 650 °C, cyclic deformation leads to a pronounced initial hardening manifesting itself in an increase of stress amplitude and a decrease of plastic strain range. Conversely, cyclic deformation curves from tests performed aboveTBDshow a marked state of saturation which is established already after few cycles. With increasing temperature, fatigue life decreases in vacuum. However, testing in air not only decreases fatigue life tremendously as compared to vacuum, but also leads to an inverse temperature effect, i. e., the number of cycles to failure increases with temperature.

In-situ observation of microstructurally small fatigue crack initiation and growth behaviors of additively-manufactured alloy 718

To reveal the effects of microstructural features on fatigue property, microscopic fatigue crack initiation and growth behavior were successively observed for rolled plate and additively-manufactured nickel base 718 alloy. Three types of additive manufacturing (AM) methods: powder bed Electron Beam Melting (EBM), Selective Laser Melting (SLM), and wire-fed Electron Beam Additive Manufacturing (EBAM) were adopted for specimen preparation to create various microstructures for comparison. The results showed that the fatigue lives of the EBM and EBAM specimens, which have a robust (001) texture, were shorter than those of the rolled plate and SLM specimens. This fatigue life difference could not be explained by the defects, because the fatigue cracks in the part of EBAM specimen were initiated along a slip plane. On the other hand, acceleration of the early stage fatigue crack growth rate (FCGR) was found in the EBM and EBAM specimens. Cross-sectional electron back scatter diffraction (EBSD) observations also showed that early stage cracks initiated and grew along the {111} slip plane; but in the EBAM specimens, the cracks continuously propagated straight to an adjacent grain due to their (001) texture. It thus appears that the low-angle grain boundaries which tend to be generated as a result of the (001) texture do not act as barriers to the penetration of dislocations; instead, they accelerate the shear mode fatigue crack growth rate in the early stages and decrease fatigue life.

The mechanical properties and fatigue responses of fiber metal nanocomposite laminates with double-edged cracks

ABSTRACT The fiber metal laminates (FMLs) of hybrid Ti/APC-2 neat and nanocomposite laminates were fabricated. Geometrically symmetric and anti-symmetric double-edged cracks were cut in FMLs. From tensile tests, we received the load vs. displacement curves, stress intensity factors of mixed mode and mechanical properties. From cyclic tests, the load vs. cycles (P–N) curves, residual life and failure mechanisms were obtained. The mechanical properties of symmetrically cracked specimens were slightly lower than those of anti-symmetrically cracked counterparts. As the crack length increases and inclination angle decreases, the fatigue life decreases. The enhancement of nanopowder improved the ultimate load and fatigue life. The local stress intensity at the crack tip dominates the fatigue responses. The piece of elliptical part was observed from cyclic tests at failure. Although the attraction of two crack tips accelerated the crack growth towards each other, the delay to failure was caused by two crack tips circling around and forming a small piece of ellipse centrally.