Tension-tension Cyclic Loading Research Articles

Towards Understanding the Effect of Loading Direction on Fatigue Crack Behavior in Mg-3Al-Zn Magnesium Alloy.

As the lightest structural metal material, magnesium alloy is increasingly widely used in aerospace, rail transportation and other fields. However, during its service, the action of alternating loads often induces fatigue fracture damage, which seriously threatens its service safety and stability. This study investigates the fatigue behaviors of Mg-3Al-Zn (AZ31) magnesium alloy along its rolling direction (RD) and normal direction (ND) under strain-controlled tension-tension cyclic loading. The strain-life curve reveals that ND specimens in which the deformation was dominated by twinning-detwinning exhibits higher fatigue life than RD specimens dominated by slip. Morphological analysis of crack patterns indicates many grain boundary fractures and long surface cracks in RD specimens, contrasting with the ND specimens' uniform distribution of short, linear cracks throughout the texture. Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) analyses suggest that crack initiation in RD specimens is likely at grain boundaries due to deformation incompatibility between the grains with soft and hard directions. Conversely, the cracks of ND specimen predominantly formed at the {10 2} twinning boundaries, owing to the strain incompatibility between the matrix and twin due to the discrepancy of basal dislocation activations.

Multiscale fatigue life prediction model for CFRP laminates considering the mechanical degradation of its constituents and the local stress concentration of the matrix

Multiscale fatigue life prediction model for CFRP laminates considering the mechanical degradation of its constituents and the local stress concentration of the matrix

Tension-tension fatigue properties of multiaxial laminated carbon/epoxy composites molded by high-pressure resin transfer molding (HP-RTM) process

Tension-tension fatigue properties of multiaxial laminated carbon/epoxy composites molded by high-pressure resin transfer molding (HP-RTM) process

A comparison of damping-based methods to identify damage to carbon-fiber-reinforced polymers laminates subjected to low-velocity impact

A method for detecting low-velocity impact damage in carbon fiber reinforced polymer (CFRP) is presented. It involves the use of the Impulse Excitation Technique (IET) and hysteresis loops to calculate the damping parameter of T700/NCT304-1 carbon/epoxy samples subjected to various low-velocity impact energies. The value of the coefficient of restitution (COR) is determined for each impact, ranging between 0.62 for the lowest impact energy to 0.48 for the highest one. The results reveal that a three-step increase in the damping parameter exists in all cases as the impact energy on the specimen increases. An abrupt jump in the damping parameter value is observed for impact energies exceeding ∼0.9 of the material's maximum capacity. Overall, at the highest impact energy equal to 3.65 J, the damping parameter increased by 43.3% compared to the pristine specimen. Additionally, two cases of cyclic tension-tension loading were applied to the specimens, with maximum stresses set at 150 MPa and 200 MPa. The measured values of plastic and elastic strain energy were used to determine the damping ratios. For both cases, the damping of the specimen subjected to the highest impact energy was ∼1.2 times greater than that of an intact specimen, with an increase pattern similar to the findings of the IET method. Optical microscope images of the specimens are provided to illustrate various damage modes observed in the composite materials.

Fatigue life assessment of notched laminated composites: Experiments and modelling by Finite Fracture Mechanics

In this paper, the coupled Finite Fracture Mechanics criterion is extended to assess the finite fatigue life of orthotropic notched laminated composites. The approach is validated through a comprehensive experimental program conducted on laminated composites under tension-tension cyclic loading conditions with two distinct lay-ups. For a given loading ratio, fatigue tests on plain and cracked specimens are first performed to provide the model inputs, the critical cyclic stress and stress intensity factor amplitudes. Fatigue tests on samples weakened by circular holes of two different radii are then used for blind predictions. Accurate predictions of the number of cycles to failure are achieved without the need for inverse calibration of material properties or deviation from standard testing procedures. Finally, a parametric study is performed to investigate the hole radius effect. It is worth mentioning that the proposed approach is general and can be applied to any notched geometry.

Assessment of early fatigue in solid plates using quasi-static component by Lamb wave propagation under group velocity matching

Assessment of early fatigue in solid plates using quasi-static component by Lamb wave propagation under group velocity matching

Quantification of process-induced effects on fatigue life of short-glass-fiber-filled adhesive used in wind turbine rotor blades

Cracks in the adhesive joints of wind turbine blades can often cause severe structural blade damage. Effects induced by the manufacturing process can have a significant impact on the cycle number toward crack initiation in the bonding material. This research compared two experimental series of neat adhesive, dog-bone-shaped specimens with different degrees of cure, fiber orientation, and porosity content, which were subjected to static and cyclic tension-tension loading. To enhance the comparability of the two coupon series, the experimental data was normalized. Normalization factors were introduced to compensate for the different properties of the two series. These factors were derived from correction models. After normalization, the S-N values of the two data series were in good agreement in the high-cycle fatigue regime. In the very-low-cycle fatigue regime, however, there was still a lack of agreement in some cases, including the static strength. Moreover, the failure mechanisms were investigated by analyzing images from the fracture surfaces and dedicated samples using X-ray microscopy. The correction models presented can be applied to estimate the design strength of adhesives. This knowledge can then be used to make rotor blade structures more resistant to crack initiation.

Fatigue crack propagation in fine-grained magnesium under low temperature tension-tension cyclic loading

Fatigue crack propagation in fine-grained magnesium under low temperature tension-tension cyclic loading

Investigation on carbon nanoparticle (CNP)-polymer sensors for fatigue monitoring of fiber-reinforced composites

Carbon nanoparticle (CNP)-polymer sensors are good candidates for monitoring structural damage. A combined numerical-analytical approach with considering the stiffness degradation of composite is proposed to calculate the resistance variations with the cyclic loads. The electro-mechanical behavior of the sensor can be simulated through the finite element analysis of a random representative volume element model and the equivalent resistance calculation of microcircuit. Then, taking the glass fiber-reinforced composite coated with the CNP-epoxy resin as example, its electro-mechanical behavior under tension-tension cyclic loading is investigated experimentally and numerically. Furthermore, by microscopic analysis, the fatigue damage monitoring mechanism of the sensor is revealed.

A comparative study on hybrid fatigue stress-life model of RC beams strengthened with NSM CFRP

Near Surface Mounted Carbon Fiber-reinforced Polymers (NSM FRP) are becoming widely used in the rehabilitation field of concrete structures. Several studies were conducted to evaluate the fatigue performance of Reinforced Concrete (RC) bridges strengthened with NSM FRP composite materials. Most stress-life (S-N) fatigue models of RC beams are based on fatigue testing that has been conducted in the region of load cycles ranging between 103 and 107. This might cause an inaccuracy in the stress-life predictions when the common S-N formulations are used. This paper presents a review of the recent research on the fatigue behavior of RC beams and proposes a hybrid fatigue stress-life model of RC beams strengthened with NSM CFRP. An analytical fatigue S-N model was developed based on experimental fatigue data of constant amplitude of tension-tension cyclic loading obtained from the literature. A hybrid formulation was used, combining both exponential and power regression analyses to enhance the accuracy of prediction in low and high cycle fatigue regions. Moreover, Muratov’s method was used to determine the endurance limit of strengthened RC beams. A three-dimensional finite element RC beam strengthened with NSM CFRP was modeled to investigate the accuracy of the proposed hybrid model. The RC beam was modeled in ANSYS with similar dimensions and material properties to experimental specimens in the literature. The hybrid model was compared to experimental and numerical data, and satisfactory precision was observed with a correlation coefficient of 0.86. The proposed hybrid model helps to provide comprehensive fatigue stress-life estimation for design purposes.

Comparison of fatigue lives between grain boundaries and component single crystals of copper bicrystals

Abstract Fatigue lives of grain boundaries (GBs) and component crystals were measured by using [123]/[335] and [5 9 13]/ [579] Cu bicrystals with a perpendicular GB at room temperature in air. The results show that the GBs were always the preferential sites for fatigue crack initiation and propagation in the two groups of bicrystals under cyclic tensiontension loading as well as push-pull straining control. When an [123]/[335] bicrystal with reduced section area was tested by cyclic tension-tension loading, the [335] component crystal always had a relatively higher fatigue life than the [123] component crystal. As a result, the fatigue life increased in the order of GB, [123] and [335] component crystals. When the two groups of bicrystals were subjected to cyclic push-pull straining, the GB of the [5 9 13]/[579] bicrystal showed a higher fatigue life than that of the [123]/[335] bicrystal, which was suggested to be partially attributed to the difference in the component crystal orientations in the two bicrystals. By using scanning electron microscopy and electron channeling contrast techniques, the fatigue damage features on the surfaces and fatigue fractography were examined. Based on the present results, the fatigue cracking mechanisms along GBs and persistent slip bands in Cu bicrystals are discussed.

Damage-entropy model for fatigue life evaluation of off-axis unidirectional composites

Damage-entropy model for fatigue life evaluation of off-axis unidirectional composites

Fatigue damage growth and fatigue life of unidirectional composites

Fatigue damage growth and fatigue life of unidirectional composites

Fatigue damage identification of SiC coated needled C/SiC composite by acoustic emission

Fatigue damage identification of SiC coated needled C/SiC composite by acoustic emission

Defect evolution during high temperature tension-tension fatigue of SLM AISi10Mg alloy by synchrotron tomography

Defect evolution during high temperature tension-tension fatigue of SLM AISi10Mg alloy by synchrotron tomography

Cyclic creep behaviour of two-phase Ti-6Al-2Mo-2Cr alloy

One of the important criteria for selection titanium alloys for discs and blades of turbine engine compressor is their fatigue and creep strength at room and elevated temperature. Fatigue and creep properties of two-phase titanium alloys show strong dependence on microstructure, especially morphology of the α and β phases which can be controlled to certain extent by proper selection of hot working and heat treatment conditions. Quantitative description of two-phase titanium alloys behaviour under loading and environmental conditions leading to combined creep and fatigue processes has been always very challenging task due to large number of factors affecting deformation and fracture behaviour of the material. In the course of the research cyclic creep behaviour of Ti-6Al-2Mo-2Cr alloy (VT3-1) was investigated and compared to low-cycle fatigue and static creep properties at the temperature of 450°C. Microstructure of the alloy was varied by means of the heat treatment. Constant load tensile creep tests were carried out. Tension-tension cyclic loading was applied at the constant stress ratio with and without hold time at maximum load. The effect of test parameters on the creep-fatigue life at elevated temperature was estimated. Characteristic features of fracture surfaces were identified by scanning electron microscopy methods.

Investigation on the Crack Evolution in Glass-Fiber Laminates Depending on the Stacking Sequence

In this paper experiments on the fatigue behavior of flat and tubular Glass Fiber Reinforced Plastics (GFRP) specimens with three different layups ([0/905/0], [0/902/01/2]s and [0/±45/01/2]s) are presented. The experiments are conducted to study the mechanics under cyclic tension-tension loading (R=0.1) until crack saturation (CDS). Fatigue testing is performed below the critical static load level where first matrix cracks can be observed. Therefore Load Levels (LLs) are derived from crack evolution curves obtained by static tests under usage of transmitted light photography. The shear lag model of Berthelot [1] is applied to the two cross-ply specimens to predict crack evolution. The results show good agreement between the prediction and the experimental data. Deviations can be found in prediction of crack evolution in [0/902/01/2]s-specimens. For predicting fatigue stiffness degradation the phenomenological model of Adden [2] is used. The results show good capabilities for predicting stiffness degradation after crack onset.

Influence of Residual Stress on Fatigue Weak Areas and Simulation Analysis on Fatigue Properties Based on Continuous Performance of FSW Joints

The fatigue weak area of aluminum alloy for a friction stir-welded joint is investigated based on the hardness profile, the residual stress measurement and the simulation analysis of fatigue property. The maximum residual stresses appeared at the heat-affected zone of the joint in the fatigue damage process, which was consistent with the fracture location of the fatigue specimen. The fatigue joint model of continuous performance is established ignoring the original negative residual stress; considering that it will be relaxed soon when the joint is under tension-tension cyclic loading. The fatigue parameters of joint model is based on the static mechanical properties of the joint that obtained from the micro-tensile tests and four-point correlation method. The predicted results for the fatigue weak locations and fatigue lives based on the continuous performance joint model are closer to the fatigue experimental results by comparison with the simulation results of the partitioned performance joint model.

Multiscale model of fatigue of collagen gels.

Fatigue as a mode of failure becomes increasingly relevant with age in tissues that experience repeated fluctuations in loading. While there has been a growing focus on the mechanics of networks of collagen fibers, which are recognized as the predominant mechanical components of soft tissues, the network's fatigue behavior has received less attention. Specifically, it must be asked (1) how the fatigue of networks differs from that of its component fibers, and (2) whether this difference in fatigue behaviors is affected by changes in the network's architecture. In the present study, we simulated cyclic uniaxial loading of Voronoi networks to model fatigue experiments performed on reconstituted collagen gels. Collagen gels were cast into dog-bone shape molds and were tested on a uniaxial machine under a tension-tension cyclic loading protocol. Simulations were performed on networks modeled as trusses of, on average, 600 nonlinear elastic fibers connected at freely rotating pin-joints. We also simulated fatigue failure of Delaunay, and Erdős-Rényi networks, in addition to Voronoi networks, to compare fatigue behavior among different architectures. The uneven distribution of stresses within the fibers of the unstructured networks resulted in all three network geometries being more endurant than a single fiber or a regular lattice under cyclic loading. Among the different network geometries, for low to moderate external loads, the Delaunay networks showed the best fatigue behavior, while at higher loads, the Voronoi networks performed better.

Experimental study on fatigue performance of adhesively bonded anchorage system for CFRP tendons

Experimental study on fatigue performance of adhesively bonded anchorage system for CFRP tendons