Fatigue Damage Evolution Research Articles

Observations of fatigue damage development in woven glass fiber-reinforced polymer composite using transmission light photography technique

Fatigue behaviour is an important aspect for consideration while handling glass fiber-reinforced polymer (GFRP) composites. A combination of (0°/90°) and (±45°) plies are gaining practical interest in engineering applications due to their excellent mechanical properties. Properties of individual above-stated plies primarily influence the behaviour of laminates. Fatigue behaviour of on-axis (0°/90°) and off-axis (±45°) fiber orientated woven GFRP laminates was investigated. Tensile and tension-tension fatigue tests were performed on the prepared test coupons according to the ASTM standard. Fatigue test was conducted until failure at maximum applied stress of 90%, 70%, and 50% of the respective ultimate strength. Damage growth was monitored in the term of debond zones by employing the transmission light photography technique. Testing process was recorded by using a digital camera. The results were established in terms of the stress-strain curve, Wöhler curve, debond zones and dynamic stiffness. The fatigue strength of off-axis laminates was much lower than the on-axis laminates. Global damage has occurred in (0°/90°) laminates while (±45°) laminate witnessed localized damage. At higher stress levels, samples were failed at shorter lifespan with aggressive damage; however, on-axis specimens survived with longer fatigue life.

Mode II Behavior of High-Strength Concrete under Monotonic, Cyclic and Fatigue Loading.

An economically efficient yet safe design of concrete structures under high-cycle fatigue loading is a rather complex task. One of the main reasons is the insufficient understanding of the fatigue damage phenomenology of concrete. A promising hypothesis states that the evolution of fatigue damage in concrete at subcritical load levels is governed by a cumulative measure of shear sliding. To evaluate this hypothesis, an experimental program was developed which systematically investigates the fatigue behavior of high-strength concrete under mode II loading using newly adapted punch through shear tests (PTST). This paper presents the results of monotonic, cyclic, and fatigue shear tests and discusses the effect of shear-compression-interaction and load level with regard to displacement and damage evolution, fracture behavior, and fatigue life. Both, monotonic shear strength and fatigue life under mode II loading strongly depend on the concurrent confinement (compressive) stress in the ligament. However, it appears that the fatigue life is more sensitive to a variation of shear stress range than to a variation of compressive stress in the ligament.

Full-field progressive fatigue damage of 3D5D braided composites with yarn-reduction: visualization, classification, and quantification

Recently, X-ray computed tomography (Micro-CT) has shown its potential for damage analysis in 3D braided composites. However, the visualization, classification and quantification of progressive damage of 3D braided composites based on Micro-CT are still lacking. The present work aims at the progressive fatigue damage mechanism of 3D5D braided composites with yarn-reduction. A novel “three-step” approach based on Micro-CT was proposed to automatically classify and quantify the fatigue damage initiation and evolution considering the position. Also, the combination techniques of Acoustic Emission (AE) and Digital Image Correlation (DIC) are employed to characterize the post-fatigue residual mechanical properties and failure mechanisms. The results indicated that the initial damage can be simultaneously found at the yarn-reduction point and edge of the specimen after 5.57% of fatigue life. Subsequently, the wedge-shaped damage near the yarn-reduction point are progressively formed. More significantly, the quantitative data of multiple defined cracks propagation is in line with the 3D visual cracks. Furthermore, the post-fatigue residual strength occurred the 38.9% decrease after experiencing the 25.1% fatigue life. It is expected that this study can provide unparalleled quantitative data for the development and validation of fatigue life prediction models of 3D5D braided composite with yarn-reduction.

Foot kinematics and leg muscle activation patterns are altered in those with limited ankle dorsiflexion range of motion during incline walking

BackgroundLarger ankle dorsiflexion (DF) is required when walking on inclined surfaces. Individuals with limited DF range of motion (ROM) may experience greater tissue stress on sloped surfaces and walk in altered gait patterns compared to the those with normal DF ROM. Research questionWould the individuals with limited DF ROM walk with distinctive ankle DF patterns compared to those with normal DF ROM on the inclined surfaces? MethodsTen Limited DF ROM (passive ROM=35.3 ± 2.7°) and nine Normal DF ROM (passive ROM=46.4 ± 4.2°) participants walked on a treadmill at five slope angles (0°, 5°, 10°, 15°, 20°) for 2 min at a self-selected speed. The peak DF angles and the peak myoelectric activity levels of the tibialis anterior (TA) and soleus (SOL) muscles were quantified during the swing and stance phases of each walking trial, and they were compared between the two groups. ResultsParticipants with limited DF ROM walked with smaller peak DF (3.1° at 0° slope ~ 8.4° at 20° slope) and greater peak TA activity in swing than those of the Normal ROM participants (3.4° ~ 12.2°), with significant differences at 20° slope. The peak DF angle in stance (Limited: 9.6° ~ 19.0°; Normal: 10.1° ~ 21.0°) did not differ between the two groups at all slopes, but the peak activity of the SOL muscle was significantly greater for the Limited group at slopes of 10° and higher. SignificanceStudy results indicate that incline walking could be more challenging to the individuals with limited DF ROM as they need to approach and push-off the sloped surfaces with more efforts of the dorsiflexor and the plantar flexor muscles, respectively. Prolonged walking on inclined surfaces may produce faster development of muscle fatigue or tissue damage than those with normal DF ROM.

Assessment of fatigue damage of prefabricated concrete composite beams with piezomagnetic signal

For prefabricated concrete structures constructed by the wet joining process, appropriate damage indicators need to be adopted to characterize fatigue damage development considering the effects of interface damage. In this study, through the cyclic load testing of 12 prefabricated concrete composite beam specimens with three different cross-section types, comparisons among the traditional damage indicators, such as deflection, stiffness, energy consumption, interface deformation and steel strain, and a new indicator – the piezomagnetic signal – are conducted. All damage indicators, including the piezomagnetic indicator, could characterize fatigue damage development. Furthermore, the piezomagnetic signal indicator could also reflect the impact of interface damage, similar to local indicators such as interface deformation and steel reinforcement strain. However, compared with local indicators, the piezomagnetic signal technique has the advantages of providing long-term monitoring provability and being a non-destructive method.

Energy dissipation and fatigue damage evolution of sandstone under different upper limit stresses

Energy dissipation and fatigue damage evolution of sandstone under different upper limit stresses

Reliability in mechanical systems projects

Sufficient safety of the parts, which determines the safety of the system specified by the technical assignment, is the necessary quality of the project, the subject of the design engineer’s attention and the customer’s requirement. An extensive task is the collection of data for iterative refinement of the resource for project details in a probabilistic aspect. It can be significantly reduced when using approximate methods for estimating the resource at intermediate stages of refining the project to the required resource with a calculated probability of failure-free operation. Thus, by the analysis of dimensionless relations of parameters of models of fatigue damage development, it is possible to obtain tools of numerical estimation of technological and constructive techniques of increase of a resource of details and their rational combination. The paper deals with the numerical measures of various directions of upgrading the fatigue life of the parts, derived from the dimensionless relations of the parameters of fatigue damage development models.

A continuum damage model for fatigue life prediction of 2.5D woven composites

Abstract A new model based on continuum damage mechanics is proposed to predict the fatigue life of 2.5D woven composites. First, a full-cell model reflecting the real microstructure of 2.5D woven composites is established in ANSYS. Subsequently, three independent damage variables are defined in the framework of the composite micromechanics to establish the component constitutive relations associated with damage. The strain energy density release rate and damage evolution equations for the matrix, fiber in yarns, and matrix in yarns are derived. Finally, the proposed model is implemented for fatigue life prediction and damage evolution analysis of 2.5D woven composites at 20 and 180°C. The results show that the numerical results are in good agreement with the relevant experimental results.

Methods for calculation and experimental evaluation of nucleation and development of the fatigue damages in tin based babbitt and babbitt lining of plain bearings

Fatigue damage to babbitt layers of plain bearings is often manifested during operation. The goal of the study is to develop a model for accumulation of the fatigue damage and destruction of antifriction materials and layers of plain bearings. A generalized fatigue diagram of tin-based babbitts including the main stages of fatigue damage and a diagram of the fatigue damage development in the antifriction layer of plain bearings are presented. The generalized model of V. V. Bolotin for damage accumulation and destruction is modified with regard to antifriction materials containing rather large structural elements. An explicit (direct) modeling of damage processes appeared possible for such materials. The model describes dissipated accumulation of microcracks (interpreted as destruction of the elements of the material structure), initiation and development of a system of short cracks, initiation and development of macro-cracks up to the limit state of the object. The model suggests discretization of the volume into sections with constant levels of complex stress state and discretization of the time axis into the intervals (blocks of loading cycles). The problem of identifying the parameters of a multistage model of the fatigue damage accumulation in the alloy is solved proceeding from the analysis of the results of testing babbitt specimens. We used the simplest optimization procedure, i.e., the method of deformable polyhedron. The parameters of the power function in the dependence of the rate of microdamage accumulation on the level of stresses are obtained. The parameters of the initiation and development of the crack system in the babbitt layer are obtained from the analysis of experimental results of studying steel-babbitt samples. The problem of calculating the durability of antifriction babbitt layers required the development of a new software. The program is examined by comparing calculated and experimental values of the durability of fatigue-tested bearing specimens forced against a rotating shaft by varying cyclic load. The calculated values of the durability match the experimental which confirms the performance of the calculated model.

Fatigue resistance evaluation of high Mn-TWIP steel through damage mechanics: A new method based on stiffness evolution

The work presented here deals with the implementation of a new methodology that allows fast and reliable determination of the fatigue strength. It is based on monitoring the specimen stiffness changes at different stress levels, as an indicator of the evolution of fatigue damage. This new rapid fatigue test uses techniques available in many laboratories, as the DIC (Digital Image Correlation) technique and common extensometers. Moreover, the obtained data are easier to handle than infrared cameras or acoustic emission systems data, and the experimental procedure to determine the fatigue limit is more evident than in the self-heating method.Experiments have been conducted in TWIP (Twinning Induced Plasticity) steel, a material used for lightweighting the structural parts of vehicles. With their excellent energy absorption capacity, TWIP steels can satisfy the part requirements in terms of crash performance, while their high tensile strength can deal with the cyclic loads acting on chassis parts. Therefore, many efforts focus on improving the fatigue strength of TWIP steels through pre-straining and/or surface treatments. However, finding the best way to improve the fatigue resistance requires time and resources that often hinder the development of the material. For this reason, a TWIP steel has been selected to check the new rapid fatigue test. The prediction made using the proposed approach is validated by comparison with conventional staircase results and fatigue crack growth standardised tests. The good agreement allows proposing the new method as a fast and efficient way to determine the fatigue resistance in metals.

Fatigue damage characterization and percolation in plain-weave carbon fiber-epoxy composites

The concept of ‘damaged unit cell’ was employed to describe the tensile fatigue damage evolution in plain-weave carbon-epoxy composites. The fatigue damage was connected to the development of cluster of damaged unit cells and their distribution, considering the measurements by thermoelastic damage analysis (TDA). Internal damage state was also observed by SEM. The experimental results showed that the size ratio of the maximum damaged unit cell cluster, Cmax, rapidly increased after the damaged unit cell ratio p exceeded 0.527, called ‘percolation threshold’ pc. This threshold announced the fatigue final failure, which occurred with fast accumulation of transverse cracks, wider local delamination and fibers breakage, once p exceeded pc. Since the relationship between the averaged thermoelastic damage response and Cmax was nearly linear, the fatigue damage evolution involved clustering of damaged unit cells. The fractal dimension D of the damaged unit cells cluster increased up to a steady state value Dc, when p exceeded pc, showing the faster fatigue damage evolution. Finally, the fatigue damage evolution was predicted using the concept of percolation and mutual interference between damaged units.

Modeling ultrasonic vibration fatigue with unified mechanics theory

A series of ultrasonic vibration tests are performed on A656 grade steel samples, at a frequency of 20 kHz. A fatigue life model based on the unified mechanics theory is introduced to predict the very high cycle fatigue life of metals. Then, the fatigue life test data results are compared with the unified mechanics theory based model simulation results. It is shown that the physics-based unified mechanics theory can predict very high cycle fatigue life very well, without the need for the traditional empirical curve fitting a fatigue damage evolution function. The model does not require any curve fitting parameters obtained from fatigue test data. However, it does require deriving analytical thermodynamic fundamental equation of the material subjected to ultrasonic vibration fatigue. The thermodynamic fundamental equation of the material formulates the entropy generation mechanisms during the fatigue process. There are more than half a dozen entropy generation mechanisms during fatigue process. Entropy is an additive property, hence, the entropy generation due to all active mechanisms can be added.

Predictive model for fatigue life in parallel-wire stay cables considering corrosion variability

This study quantitatively assessed the influence of corrosion and its variability on the stay cable fatigue life. The corrosion-life inverse equal rank assumption is proposed to identify the order of wire failures, with the wires with the largest level of corrosion failing first. Recursion formulas of stay cable fatigue life are established based on models of the evolution of fatigue damage for multi-step loading, assuming the loading redistribution after the failure of each wire. The bounds for the cumulative distribution function for stay cable fatigue life are estimated using order statistics, and Monte Carlo simulation is conducted to simulate the stay cable fatigue failure. As the variability in the corrosion of the wires increases, the variability in the fatigue life of the wires and stay cables increases, resulting in a decrease in the stay cable fatigue life. The stay cable fatigue life decreases sharply with the increase in the corrosion degree of the wires, with the effect being more pronounced for larger corrosion variability. Moreover, the effect of the corrosion variability on the stay cable fatigue life is much significant for larger corrosion levels and under lower stress ranges.

Highly Sensitive Nonlinear Identification to Track Early Fatigue Signs in Flexible Structures

Abstract This study describes a physics-based and data-driven nonlinear system identification (NSI) approach for detecting early fatigue damage due to vibratory loads. The approach also allows for tracking the evolution of damage in real-time. Nonlinear parameters such as geometric stiffness, cubic damping, and phase angle shift can be estimated as a function of fatigue cycles, which are demonstrated experimentally using flexible aluminum 7075-T6 structures exposed to vibration. NSI is utilized to create and update nonlinear frequency response functions, backbone curves and phase traces to visualize and estimate the structural health. Findings show that the dynamic phase is more sensitive to the evolution of early fatigue damage than nonlinear parameters such as the geometric stiffness and cubic damping parameters. A modified Carrella–Ewins method is introduced to calculate the backbone from nonlinear signal response, which is in good agreement with the numerical and harmonic balance results. The phase tracing method is presented, which appears to detect damage after approximately 40% of fatigue life, while the geometric stiffness and cubic damping parameters are capable of detecting fatigue damage after approximately 50% of the life-cycle.

Suitability of DIC and ESPI optical methods for monitoring fatigue damage development in X10CrMoVNb9-1 power engineering steel

The aim of this research was to compare the effectiveness of two different optical measurement techniques (digital image correlation—DIC and electronic speckle pattern interferometry—ESPI) during fatigue damage development monitoring in X10CrMoVNb9-1 (P91) power engineering steel for pipes. The specimens machined from the as-received pipe were subjected to fatigue loadings and monitored simultaneously using DIC and ESPI techniques. It was found that DIC technique, although characterised by lower resolution, was more effective than ESPI. DIC allows to monitor the fatigue behaviour of steel specimens and accurately indicate the area of potential failure even within the initial stage of fatigue damage development.

Statistics-based numerical study of the fatigue damage evolution in the microstructures of WC-Co hardmetals

In industrial applications, hardmetal tools are often exposed to fatigue loads. This paper proposes a micromechanics-based numerical approach for evaluating the fatigue performance of WC-Co hardmetals. Because the mechanical response of the material is sensitive to the coexisting toughening and damage mechanisms of the ductile binder matrix, this study employed a Chaboche model to precisely present the kinematic hardening behavior and describe the material plasticity of the binder phase. The progressive fracture in the microstructure is modeled by an implicit damage mechanics model implemented in the commercial solver Abaqus/Standard. The numerical study successfully simulated different stages of the fatigue failure process by modeling the damage behavior in the microstructure and reproducing the compromising roles of the ductile binder under the fatigue regime. In addition, the study also emphasizes the need to view fatigue behavior from a statistical perspective owing to the high level of microstructure heterogeneity. By studying the cyclic responses of 50 representative volume element models converted from real scanning electron microscope images, the study revealed how the microstructural characteristics of the hardmetal interact with the imposed external loading and how these two factors jointly determine the load-bearing capacity of the material.

Damage evolution of 3D woven carbon/epoxy composites under the tension–compression fatigue loading based on multi damage information

The fatigue damage mechanisms of 3D woven composites are very complex. In this work the tension–compression (T-C) fatigue damage evolution of 3D woven composites is investigated using a multi-scale method. To avoid the buckling failure during the T-C fatigue tests, a novel anti-buckling device is designed. The authors combine the macro damage information (i.e., axial stiffness and surface temperature) and the meso-damage information (i.e., detection results by synchrotron radiation computed tomography (SRCT)) to investigate the fatigue damage evolution. The results show that the T-C fatigue process can be divided into two stages. The stiffness decreases slowly in a linear form in Stage I, and then decreases rapidly to final failure in Stage II. Most of the fatigue damage occurs in Stage II. The SRCT results can reveal the damage modes in either fatigue stage, in which the warp yarn breakage is the critical damage mode.

A coupled model for investigating the interfacial and fatigue damage evolution of slab tracks in vehicle-track interaction

Modeling, evaluation and prediction of slab track damage and its evolution are nowadays challenge and hot topics, in which the computer modeling program lies a foundation for vehicle-track dynamic analysis subject to slab track damage except the experimental research. In this work, the finite element modeling methods and related computer modules are presented to compile a simulation program to evaluate the slab track damage evolution accompanied by vehicle-track dynamic interaction, where the moving vehicle is modeled as a multi-rigid-body system with the primary and secondary suspensions, and the Bernoulli-Euler beam, thin-plate and solid finite element and spring-dashpots are introduced to model the track system. The fatigue damage constitutive models of the concrete slabs and viscoelastic filling layers, and the interfacial cohesive zone model, are set as the criteria to control and characterize the damage evolution of slab tracks. Apart from model validations, numerical studies are conducted to quantitatively show influence of track irregularities on slab track damage evolution and the slab track damage on vehicle-track system response. It illustrates the necessity of considering the combined fatigue and interfacial damages of slab tracks instead of separately accounting for the fatigue or interfacial damage.

Evaluation of fatigue performance of cement-treated composites based on residual strength through discrete element method

Fatigue damage is the process of material fatigue failure caused by cyclic loading, and the development of damage degrades the material properties. This paper aims to investigate the fatigue degradation law of cement-treated base (CTB) materials using a discrete element method (DEM) simulation technique. A fatigue evolution model was adopted to characterize the time-dependent fatigue damage under cyclic loading. Virtual semi-circular bending (SCB) fatigue and residual strength tests at different fatigue stages were performed on mesoscale DEM model to evaluate the fatigue damage of CTB material. With residual strength variable, the fatigue damage model was established to reveal the accumulation of damage. The results show that the residual strength evolution nearly appears an exponential correlation with the fatigue stages. In the first stage, the strength degradation is stable and appears as approximately linear. At about 80% of the fatigue life, the degradation rate is significantly accelerated. The residual strength degradation rate is related to the initial stress level and decreases with the increase of stress ratio. At the same fatigue life stage, the greater residual strength attenuation will be generated with a lower load level. The fatigue damage evolution model indicates the fatigue damage accumulation approximately linearly in the early stage and rapidly in the late stage. The late fatigue stage has the main contribution to fatigue failure. The degradation law demonstrates the lower the load level is, the more the damage accumulation at the same fatigue life stage will be, and the corresponding critical damage is greater. Moreover, based on the strength degradation law, a prediction model is established to evaluate the residual fatigue life of pavement base material.

Investigation on the macro-meso fatigue damage mechanism of rock joints with multiscale asperities under pre-peak cyclic shear loading

The fatigue damage mechanical behaviours of rock joints under pre-peak cyclic shear loading are one of the key factors affecting the dynamic stability of slopes. In this study, the macro-meso fatigue damage mechanism of rock joints with multiscale asperities, when considerthe influence of the normal stress, shear rate, shear amplitude, first-order asperity angle, number of shear cycles and joint morphology, were investigated using experimental and numerical approaches under a constant normal load (CNL). The laboratory pre-peak cyclic shear experiments on the saw-tooth rock joints with different first-order asperity angles, i.e., 30°, 45° and 60°, and the same second-order asperity angle of 45°, were first conducted under different influence factors mentioned above. Six evolution stages of the shear stress with the shear displacement, i.e., initial nonlinear shear contraction deformation, approximate linear elastic shear dilation deformation, cyclic fatigue damage deformation, plastic deformation of the local compression-shear fracture, full plastic deformation of the stress brittle drop and ideal plastic flow deformation, were obtained. Additionally, the variation rules of the influence factors mentioned above with the peak (and residual) shear strengths and the cumulative shear (and normal) displacements were explored. Subsequently, the PFC2D discrete element method was used for the meso numerical simulations, in which the meso fatigue damage evolution processes of the saw-tooth and wavy rock joints were simulated considering more number of shear cycles. Meanwhile, the change rules of the meso fatigue damage crack number (and energy) with the shear displacement (and the number of cycles), and the distribution characteristics of the meso fatigue damage particles were observed. Based on the good agreement between the macro experimental results and the meso numerical observations, the macro-meso fatigue damage failure modes of rock joints can be generally summarized as three basic types, i.e., compacting – climbing failure mode, climbing – cyclic abrading – extruding – gnawing failure mode and gnawing – sliding failure mode.