Fatigue Behavior Of Materials Research Articles

Characterization of compressive fatigue behavior and acoustic emission analysis of Ti6Al4V cellular lattice materials fabricated by laser powder bed fusion

AbstractThis study investigates the mechanical properties and fatigue performance of Ti6Al4V cellular lattice materials (CLMs) featuring five distinct unit cell types (BCC‐Z, BCC, Octet, Truncated cuboctahedron [TCO], and Trabecular) at a relative density of 25%. Compression tests were conducted to assess static properties, including Young's modulus and yield strength. Subsequently, compression–compression fatigue tests (R = 0.1) were performed to evaluate fatigue behavior. Acoustic emission analysis was employed during static and fatigue tests to explore the potential for failure prediction. Results reveal that BCC‐Z and TCO exhibit slightly higher Young's moduli, surpassing 20 GPa, while BCC, Octet, and Trabecular display moduli ranging from 6 to 12 GPa. Regarding normalized fatigue behavior, BCC‐Z demonstrates superior fatigue resistance, followed by TCO. Notably, the acoustic emission parameters significantly correlate with the unit cell type. Lastly, a strong relationship between the initiation of failure and changes in acoustic emission parameters is observed, establishing a meaningful link between the static and fatigue curves and acoustic emission results.

Experimental investigation on fatigue and fracture behaviour of cold recycling materials

Cold Recycled Material (CRM) has emerged as a highly innovative road construction material, offering numerous advantages over conventional Hot Mix Asphalt (HMA), such as reduced construction costs, decreased energy consumption, and enhanced resistance to reflective cracking. CRM is primarily composed of Reclaimed Asphalt (RA) and bitumen emulsion, with the addition of cement as a co-binder. However, the presence of cement in CRM can lead to increased susceptibility to cracking under heavy traffic loads. In this study, the fracture-fatigue behaviour of CRM modified with by-product fillers was investigated in order to improve the overall performance of CRM mixtures. The Cyclic Indirect Tensile Fatigue test (CIT-CY) and Semi-Circular Bending (SCB) fracture tests were conducted on the CRM mixtures and mortars, respectively. The findings reveal that CRM materials incorporating specific fillers demonstrated a balanced combination of fatigue and fracture resistance, indicating the potential for these modified CRMs to enhance road construction applications.

A novel non-linear peridynamic model for quasi-brittle materials under cyclic loading

In the present paper, a novel non-linear peridynamic (PD) model is proposed to numerically simulate the fatigue behaviour of quasi-brittle materials. The model implements a non-linear degradation law for the bonds, function of the number of loading cycles. More precisely, a calibration function and a calibration parameter are included in such a law. The novel PD model is applied to simulate cyclic three-point bending experimental tests performed on concrete notched beams (available in the literature). The results are presented in terms of fatigue lifetime, Paris law parameters and crack path.

Failure Analysis and Fatigue Behavior of Natural Fibers Reinforced Composite Materials under Cyclic Loading

This research investigates the failure analysis and fatigue behavior of composite materials reinforced with a combination of glass fiber, sisal fiber under cyclic loading conditions. The study aims to elucidate the synergistic effects of these diverse natural fibers in enhancing the mechanical properties and fatigue resistance of the composite materials. Experimental methods, including mechanical testing and microscopic analysis, are employed to discern the individual contributions of each fiber type and their combined influence on failure modes and fatigue life. The project seeks to provide valuable insights into the optimal integration of glass, sisal to achieve a balanced composite material that exhibits superior durability and performance. The outcomes of this research contribute not only to the advancement of natural fibers composites but also offer practical guidelines for designing resilient materials for various engineering applications.

On the fatigue behaviour of epoxy-based nanostructured composite materials

Epoxy composites and nanocomposites enable the creation of high-performance structures and innovative designs. However, there is limited research focused on their fatigue characterization. The purpose of this study is to analyze the fatigue resistance results of nanostructured composite materials made with an epoxy matrix of Diglycidyl Ether of Bisphenol F and 9,9-bis(3-chloro-4-aminophenyl) fluorine (DGEBF-CAF) reinforced with 5%wt of elastomeric nanoparticles with an average diameter of 200 nm. The tests are conducted at variable load and frequency using Rotating Bending (R-B) and Tensile-Tensile (T-T) tests, and the results are compared to those obtained with pure resin. The occurrence of thermal fatigue phenomena during the tests is monitored using a thermal camera. The results confirm that pure epoxy resin exhibits poor crack propagation resistance due to its low ductility and toughness, and the introduction of a second phase leads to an improvement of approximately 3 times in T-T tests and 5 times in R-B tests.

A novel approach of fatigue testing and evaluation of electronic systems based on phase tracking

This paper presents an experimental approach to perform fatigue testing of a lightly damped electronic assembly subjected to harmonic excitation. By leveraging the power of the phase locked loop control algorithm, our proposed work aims to accurately track the phase of the system. This innovative approach enables precise measurement of the drop in resonant frequency due to fatigue, enhancing overall damage prediction. The proposed approach exploits the characteristics of the materials that the phase at the resonance is constant and for a lightly damped system, the value is close to pi/2. In the event that the test article experiences fatigue, and the resonant frequency undergoes a change, the controller will promptly adapt to the new frequency while upholding a constant phase, ensuring the uninterrupted continuity of the testing process. The proposed approach is demonstrated by using the Ball Grid Array (BGA) electronic package as an example, where the test setup, data acquisition, and data monitoring for identifying the interconnect failure are presented. Failure analysis of the test article shows that the primary failure mode is the solder joint failure at the Intermetallic (IMC) layer. A finite element model is developed and correlated with experimental modal analysis to accurately estimate maximum stress and deflection in solder joints. By utilizing the obtained results, one can create a more accurate SN curve for the tested material. This will allow for a better understanding of the material's fatigue behavior and enable more precise predictions of its durability in real-world applications.

Corrosion fatigue performance of modified 17-4PH in simulated geothermal environment

Corrosion fatigue behavior of a new candidate material for geothermal turbine blade, modified 17-4PH, was investigated in detail. The environmental acceleration of crack growth rate was discussed in terms of ∆K. Fracture surface and side surface were observed by SEM. The crack path on side surface was also analyzed by EBSD. Then, the corrosion mechanism was discussed. Striation width on the fracture surface was compared to the crack growth per cycle. Since pitting occurred during the corrosion fatigue test, anodic polarization test was exercised to measure the pitting potential, and the cause for the pitting was also discussed. The hardness was also characterized by micro-hardness test and auger electron mapping.

Fatigue limit estimation of metals based on the thermographic methods: A comprehensive review

AbstractInfrared thermography has been under review in the last 30 years due to its versatility and potential in the detection of the thermal signature associated with intrinsic energy phenomena due to dissipative processes, specifically those relying on mechanical fatigue. Nowadays, it is a well‐established technique that can support mechanical and structural engineers to implement a damage‐tolerant design, assess the residual life, and finally characterize the fatigue behavior of materials. The aim of this work is to review all thermography‐based approaches and procedures for fatigue limit estimation by rapid tests, drawing considerations on the applicability of thermal methods in fatigue assessment of mechanical components, proposing the capabilities of different thermal indices in fatigue assessment, and discussing the pros and cons of each method as well as the open points. On one hand, this review intends to sum up what has already been done in the field; on the other hand, it provides a guideline to direct new researches toward issues that should be resolved or understood.

Low-cycle fatigue mechanical behavior of 30CrMo steel under hydrogen environment and numerical verification of chaboche model

In order to investigate the fatigue behavior of the hydrogen storage material, 30CrMo steel, in a hydrogen environment, an electrochemical hydrogen charging method was employed. Low-cycle fatigue experiments were conducted on the material to obtain half-life stress–strain hysteresis curves, cyclic response characteristics, and strain-life relationships under different hydrogen charging durations. The results indicate that the material exhibited an overall cyclic softening behavior, transitioning from ductile fracture to brittle fracture after hydrogen charging, resulting in a significant reduction in fatigue life. The Manson-Coffin formula was fitted based on material cyclic response characteristics and strain-life relationship curves. Additionally, fatigue toughness and Chaboche kinematic hardening models were fitted based on low-cycle fatigue test data. Finite element analysis was used to validate the accuracy and reliability of the Chaboche kinematic hardening model. The Chaboche kinematic hardening model showed minimal error compared to experimental data and accurately described the influence of hydrogen on the low-cycle fatigue mechanical behavior of 30CrMo steel.

Artificial Neural Network-based fatigue behavior prediction of metals and composite materials

This article presents a study devoted to predicting the fatigue behavior of two different materials: aluminum alloy AL-2024-T6 and glass fiber composite samples. The approach used in the study involves the use of artificial neural networks (ANNs) to develop accurate models for predicting the fatigue life of these materials at various skewness ratios (R). For the first case study, the S-N curve of tensile-tested AL-2024-T6 was predicted for different values of R using a few sets of data for learning. The model was then tested on the same values of R as the learning set, as well as on a different value of R (-0.4), to demonstrate the ability of the model to predict fatigue data under varying conditions. The results showed that the model was capable of accurately predicting the fatigue life of AL-2024-T6 for different values of R. For the second case study, the stiffness degradation of bending-tested glass fiber woven composite samples was predicted for different values of R using ANN. Different layups of composite samples were considered in this study. The model was trained on a few sets of data and tested on the same and different values of R, demonstrating the ability of the model to accurately predict stiffness degradation of composite samples under varying coefficients of asymmetry. The results of both case studies showed that ANN-based models can be effective in predicting the fatigue behavior of different materials tested using different methods under varying coefficients of asymmetry. These findings have practical implications for industries involved in the design and manufacturing of materials, particularly in the aerospace and automotive sectors, where fatigue behavior is critical to the structural integrity of components.

Fatigue Behaviour of Cord Rubber Composite Materials in Air Spring Bellows of Rail Vehicles

Bogies of rail vehicles for passenger coaches and traction units commonly contain air spring systems as secondary spring stages. In the development and design of spring stages, it is necessary to ensure precise knowledge about the material properties and fatigue behaviour of the air spring bellows.The aim of this work is to systematically investigate the damage mechanisms evaluated at air spring bellows on sample level and to analyse the fatigue strength of the base material under different load conditions. The specially developed small-scale sample is biaxially loaded and different layups are examined at varying load levels. In the tests with different parameters, an increase in the mean value of the longitudinal displacement by 20 % has proved to act as a suitable failure criterion. In addition to the purely optical damage analysis, micro computed tomography analysis was carried out.In this study, four layered samples with a fibre angle of ±15, ±25 and ±35 degrees in respect to the longitudinal direction are examined. A global evaluation of the service life tests reveals that under comparable load conditions, the fibre angle exhibits a clear influence on the fatigue strength. The increase of 10 degree in fibre angle roughly results in a 15 % reduction of the tolerable lateral displacement amplitude at a number of fifty thousand load-cycles which commonly acts as design lifetime. In a second step, a local analysis based on an analytical approach is presented. With the help of the fibre strain amplitude calculated, all fatigue test data points can be unified to a master S/N-curve leading to an elaborated design model of cord rubber composite materials used in air spring bellows of rail vehicles.With the help of the presented methodology utilizing the developed representative small-scale sample testing procedure and evaluation approach, a time- and cost-efficient fatigue design is facilitated.

Fatigue crack growth rate and propagation mechanisms of SiC particle reinforced Al alloy matrix composites

PurposeThis study aims to investigate the fatigue crack propagation behavior of SiC particle-reinforced 2124 Al alloy composites under constant amplitude axial loading at a stress ratio of R = 0.1. For this purpose, it is performed experiments and comparatively analyze the results by producing 5, 10, 15 Vol.% SiCp-reinforced composites and unreinforced 2124 Al alloy billets with powder metallurgy (PM) production technique.Design/methodology/approachWith the PM production technique, SiCp-reinforced composite and unreinforced 2124 Al alloy billets were produced at 5%, 10%, 15% volume ratios. After the produced billets were extruded and 5 mm thick plates were formed, tensile and fatigue crack propagation compact tensile (CT) samples were prepared. Optical microscope examinations were carried out to determine the microstructural properties of billet and samples. To determine the SiC particle–matrix interactions due to the composite microstructure, unlike the Al alloy, which affects the crack initiation life and crack propagation rate, detailed scanning electron microscopy (SEM) studies have been carried out.FindingsOptical microscope examinations for the determination of the microstructural properties of billet and samples showed that although SiC particles were rarely clustered in the Al alloy matrix, they were generally homogeneously dispersed. Fatigue crack propagation rates were determined experimentally. While the highest crack initiation resistance was achieved at 5% SiC volume ratio, the slowest crack propagation rate in the stable crack propagation region was found in the unreinforced 2124 Al alloy. At volume ratios greater than 5%, the number of crack initiation cycles decreases and the propagation rate increases.Originality/valueAs a requirement of damage tolerance design, the fatigue crack propagation rate and fatigue behavior of materials to be used in high-tech vehicles such as aircraft structural parts should be well characterized. Therefore, safer use of these materials in critical structural parts becomes widespread. In this study, besides measuring fatigue crack propagation rates, the mechanisms causing crack acceleration or deceleration were determined by applying detailed SEM examinations.

Damage assessment during ultrasonic fatigue testing of a CF-PEKK composite using self-heating phenomenon

The knowledge and experience with the very high cycle fatigue (VHCF) behavior are limited compared to the low cycle and high cycle fatigue behavior of fiber-reinforced composite materials. Accelerated cyclic loading using an ultrasonic fatigue testing system is one potential solution to evaluate the longevity of composite materials within a reasonable time. Insufficient sampling rates and the inherent inaccuracies of non-contact measurement devices pose critical challenges in the adaptation of accelerated fatigue experiments. This study aims to overcome these challenges by combining the temperature response of the composite specimen and the input parameters for the dynamic response of the in-house developed ultrasonic fatigue testing system to detect damage before failure. Increasing- and constant-amplitude fatigue experiments were conducted on a carbon fiber satin fabric-reinforced poly-ether-ketone-ketone (CF-PEKK) composite material. These experiments were carried out under three-point bending loading conditions at a cyclic frequency of about 20 kHz. Various parameters, such as the surface temperature, the cyclic displacement, and the input resonance parameters of the ultrasonic generator, were recorded during these experiments. The VHCF behavior of the CF-PEKK material system was characterized based on these results and through digital light optical microscopy.

EFFECT OF MACHINABILITY OF GNP–GFRP COMPOSITES ON TENSILE STRENGTH AND FATIGUE BEHAVIOR

The paper focuses on the cutting behavior of Glass Fiber Reinforced Polymer (GFRP) composites and GNP–GFRP composites that contain varying amounts of Graphene Nano Platelets (GNP). GFRP composites are increasingly being used in a variety of industrial applications due to their excellent mechanical properties, such as high strength, stiffness, and low weight. However, their machining and cutting behavior can be challenging due to the presence of the reinforcing fibers. Therefore, the study aims to investigate the machining behavior of GFRP composites and the effect of adding GNP on their cutting behavior. The effect of different parameters such as cutting speed, feed rate and reinforcement rate on cutting forces and delamination factor is investigated. In addition, the tensile strength and fatigue behavior of the composite materials with the best and worst delamination factors were also determined. Addition of up to 0.2 wt.% of GNP to GFRP composites resulted in an increase in cutting forces and delamination factor when drilling GFRP composites. While the cutting force and delamination factor decreased with the increase in cutting speed, the cutting force and delamination factor increased with the increase in the feed rate. Analysis of variance (ANOVA) was performed to determine the effects of drilling parameters and reinforcement ratio on cutting force and delamination factor according to full factorial experimental design. The most efficient factor on the cutting forces is found to be feed rate (84.97%), followed by the reinforced rate (6.48%) and cutting speed (6.13%). The most efficient factor on the delamination factor is determined to be feed rate for (44.49%), followed by the reinforced rate (29.20%) and cutting speed (21.73%).

Application of digital image correlation to derive Paris' law constants in granite specimens

This study investigates the effectiveness of Digital Image Correlation (DIC) as a powerful tool for deriving Paris' law constants in black granite specimens subjected to cyclic loading. A series of monotonic and cyclic loading tests on rectangular granite specimens yields valuable insights into geological material fatigue behavior, establishing monotonic tests as foundational references for subsequent cyclic loading experiments. Innovative DIC software application enables precise tracking and analysis of Crack Mouth Opening Displacement (CMOD) values, revealing distinct, observable patterns in crack growth during cyclic loading. A notable contribution lies in the implementation of a compliance calibration technique integrating Finite Element Method (FEM), facilitating the direct linkage between CMOD values and effective crack lengths, resulting in highly accurate Paris' law constants. With an average of 1.04 E −7 for C and 8.95 for m, these constants are essential for predicting fatigue crack propagation in granite specimens. This research underscores DIC's efficacy as a pivotal fatigue analysis tool, enhancing predictive capabilities for structural safety and durability assessments in geological materials, while emphasizing the crucial role of advanced imaging and numerical techniques in material science and structural engineering. It lays a robust foundation for future geological material studies and comprehensive structural integrity assessments.

Low cycle fatigue behaviour of cellular materials: Experimental comparative study of strut-based and gyroid structures made of additively manufactured 316L steel

Cellular materials are an attractive option to improve mechanical properties in lightweight design. Given their complex geometry, cellular materials present small features at the meso-scale that make them highly susceptible to fatigue failures. Fatigue of these materials has been receiving adequate attention only in the last few years, nevertheless, studies of low cycle fatigue (LCF) behaviour are extremely scarce and fragmented. In this study, 316L steel strut-based (FBCCZ) and gyroid cellular specimens were successfully manufactured by laser-powder bed fusion and tested in the LCF regime, considering their post-manufacturing morphological characteristics. The cyclic elastoplastic response revealed a higher stiffness for the strut-based than the gyroid cellular structure. The latter, in contrast, exhibited higher fatigue strength in strain-control mode, thanks to the absence of severe stress and strain raisers when compared to the strut-based counterpart. Overall, strain-life curves of both types of cellular materials are shifted to lower number of cycles to failure with respect to the base material. Detailed fractographic analyses revealed complex and tri-dimensional fracture surfaces for the gyroid specimens, whereas the strut-based lattice displayed planar fracture surfaces.

Fatigue and Fracture Behaviors of Short Carbon Fiber Reinforced Squeeze Cast AZ91 at 20 °C and 250 °C

AZ91 is one of the most broadly used Mg alloys because of its good castability and reasonable mechanical properties. Strengthening AZ91 with carbon short fibers aims to increase tensile and fatigue strength, creep, and wear resistance. One of the proposed applications of reinforced AZ91 is the production of pistons for trucks. Such reciprocating parts are subjected to alternating fatigue loads which can lead to fatigue failure. In this respect, studying the tensile and fatigue behavior of materials subjected to such loading conditions is of great interest. The alternating low-cycle fatigue (LCF) and high-cycle fatigue (HCF) of unreinforced AZ91 and carbon fiber-reinforced AZ91 (AZ91-C) were investigated at 20 °C and 250 °C. Tensile tests were carried out at the same testing temperature to find the appropriate fatigue testing stress and strain for stress-controlled and strain-controlled tests, respectively. The fatigue curves of stress against the number of cycles (S–N) revealed that the composite AZ91-C’s fatigue strength was 55 MPa under HCF, while that of the matrix alloy AZ91 was only 37 MPa at 250 °C. Fracture investigations were conducted on the broken test samples. The fracture approach in the matrix material (AZ91) is mixed ductile/brittle containing fatigue serration, fiber fracture, and separation in the reinforced material (AZ91-C).

Effect of Corrosive Environment on the High-Cycle Fatigue Behavior of Reinforced Concrete by Epoxy Resin: Experimental Study.

Large engineering structures made of various materials, including concrete (e.g., bridges, dams, buildings, and multilevel car parks), steel (e.g., power towers, ships, and wind turbines), or others, are often subjected to severe vibration, dynamic, and cyclic loads, which lead to crack initiation, crack growth, and finally structural failure. One of the effective techniques to increase the fatigue life of such structures is the use of reinforced materials. In the meantime, environmental factors, such as corrosion caused by corrosive environments, also affect the fatigue behavior of materials. Therefore, the main purpose of this paper is to study the influence of corrosive environment on the high-cycle fatigue (HCF) behavior of concrete reinforced by epoxy resin. For this purpose, five corrosive environments with different intensities, including fresh air, water: W, sea water: SW, acidic: AC, and alkaline: AL, were considered and the laboratory samples of conventional concrete (CC) and polymer concrete (PC) were immersed in them for one month. Next, axial fatigue tests were performed under compressive-compressive loading with a frequency of 3 Hz on cylindrical specimens. Moreover, to achieve reliable results, for each stress amplitude, the fatigue test was repeated three times, and the average number of cycles to failure was reported as the fatigue lifetime. Finally, the stress-life cycle (S-N) curves of different states were compared. The results showed that polymer concrete can resist well in corrosive environments and under cyclic loads compared to the conventional concrete, and in other words, the epoxy resin has performed its task well as a reinforcer. The results of fatigue tests show that the load bearing range of 10 tons by CC has reached about 18 tons for PC, which indicates an 80% increase in fatigue strength. Meanwhile, the static strength of samples in the vicinity of fresh air has only improved by 12%.

Fatigue Analysis of Novel Aortic Valve Stent Using Finite Element Analysis

Aortic stenosis and Regurgitation are the common heart valve diseases that about 20% of the US population get diagnosed with each year. Recent advances in minimally invasive surgical techniques like transcatheter aortic valve replacement (TAVR) have paved the way for high-risk patient treatment with minimal hospital stay and use of anesthetic. While the patient data on prosthetic stent based aortic valve durability from the last decade has instilled confidence, this data is still considered inadequate for large scale adoption of TAVR therapy for low and medium risk patients. As one of the leading failure modes for the Nitinol based prosthetic stents is material fracture due to cycling fatigue, it is critical to identify a method to accurately predict it. While the historic scientific literature available indicates the presence of stress based, strain based and damage-tolerance analysis-based assessments of fatigue behavior of Nitinol material, there still exists a gap specifically for accurate prediction of fatigue life of Nitinol based prosthetic stents using computational methods like finite element analysis. This article presents a case study of estimating the fatigue life of novel aortic valve when subjected to physiological loading conditions using FEA while using minimal computational resources. This FEA and strain-based approach using constant-life diagram method of fatigue estimation will allow for preliminary evaluation of fatigue life and make design and process changes before fabrication and testing of prosthetic aortic.

Effects of pulsed laser hardening of cylindrical surfaces on fatigue behavior

The issues of the of laser hardening of the plain bearing effects on the fatigue strength of the crankshaft neck journal are discussed in this article. The crankshaft destruction of the crankshaft leads to catastrophic consequences, especially for heavy diesel engines. The article substantiates the assertion of a decrease in the fatigue strength of steels after pulsed laser hardening treatment of the friction surface to increase the wear resistance of a plain bearing. The process of formation of a surface hard layer of steel and the formation of dimple-shaped stress concentrators on it after interaction with a laser pulse is studied. Factors affecting the fatigue behavior of materials are analyzed. Particular attention is paid to the formation of a residual stress state in the surface layer and the role of surface defects on the fatigue behavior of steel. The assumption about the possibility of reducing the decrease in fatigue strength by optimizing the technological parameters of laser processing is substantiated. On the basis of the study, it is proposed to limit the energy of the laser pulse, preventing the surface from melting.