Characterization Of Fatigue Behavior Research Articles

Characterization of fatigue behavior of 3D printed pneumatic fluidic elastomer actuators

Soft robots have gained significant interest due to their high flexibility and adaptability to various working conditions. Recent advancements in engineering and innovative materials have enabled the design and production of sophisticated soft robotic systems with enhanced capabilities. This study aims to evaluate the fatigue behavior of bellow-type pneumatic soft actuators fabricated through fused filament fabrication (FFF) using thermoplastic polyurethane (TPU), compared to silicone rubber cast actuators. The actuators were equipped with resistive flex sensors to monitor bending motion, and fatigue tests were performed with cycles of inflation and deflation until failure. Results showed that 3D printed TPU actuators could withstand a significant number of cycles before failure, with an average of 6410 cycles at 3 bar pressure, compared to 3439 cycles at 1 bar pressure for the silicone actuators. The study identified a set of fabrication parameters that positively affect the durability of TPU actuators, providing valuable insights for replicating these results. Additionally, the study established a plausible range of utilization for 3D-printed FFF actuators in terms of the number of cycles they can endure, offering critical data for engineers and designers to make informed decisions about the design and application of these actuators in various practical scenarios. The findings demonstrate the potential of FFF for producing durable, long-lasting pneumatic soft actuators.

Characterization of fatigue behavior of AA2024‐T351 aluminum alloy

AbstractThe paper aims to investigate the fatigue behavior of the widely used AA2024‐T351 aluminum alloy in the aircraft industry. An experimental program was conducted to study the fatigue life and damage behavior under symmetrical tensile‐compressive loading. Cyclic tests in the low cycle fatigue regime were performed under fully reversed total strain amplitudes from 0.6% to 1.2%. The AA2024‐T351 alloy exhibited cyclic hardening until failure. Symmetric high cycle fatigue tests were also performed and the parameters for fatigue life estimation using the Manson–Coffin–Basquin model were identified. Elasto‐plastic behavior was analyzed through stress–strain hysteresis loops, evaluating kinematic and isotropic hardenings. Kinematic hardening was found to be strain amplitude dependent, unlike the isotropic hardening. The evolution of the isotropic variable with the percentage of fatigue life could be described by an exponential law. Fractography investigations showed crack initiation at the specimen border with quasi‐cleavage and then crack propagating by striation before ductile fracture.

Normalized characterization method for fatigue behavior of cement-treated aggregates based on the yield criterion

The objective of this paper is to propose a normalized characterization method based on the yield criterion to eliminate the impacts of different stress models on the fatigue behaviors characterization of cement-treated aggregates. Based on the theory of octahedral shear stress strength and yield surface mode, the yield surface of cement-treated aggregates was established with four-point bending, compression, and indirect tensile strength value under different loading rates. Then, the fatigue stress and corresponding ultimate strength could be characterized by the yield surface, uniformly and uniquely. In the yield surface space (I1, J2), the fatigue stress growth route from initial stress to ultimate strength was identified as fatigue stress path. Based on the fatigue stress path, the fatigue stress ratios related to loading rate and stress model were calculated. With these stress ratios, the conventional S-N fatigue equation was modified, on the basis of which a normalized characterization method of fatigue behavior was proposed to characterize the fatigue behavior of cement-treated aggregates. Compared with the traditional characterized method, the normalized characterization method has considered the influence of loading rate and stress model on strength and fatigue test results. The test results demonstrated that different strength and fatigue test results were obtained under distinct stress model and loading rates. All strength values have been expressed indiscriminately in the yield surface. With the normalized characterization method, a unique fatigue curve was gained for cement-treated aggregates under different loading rates and stress models. Therefore, findings of this work realized the normalization characterization of fatigue behavior of cement-treated aggregates.

Characterization of fatigue behavior of Al-Li alloy 2099

Experiments and modeling were performed to quantify the microstructure-fatigue properties relationship of wrought aluminum-lithium alloy 2099 (AA2099) plate. Microstructural morphology was examined via optical microscopy, SEM, and TEM techniques. The mechanical properties were determined through monotonic tensile and fully reversed fatigue testing. The rolled AA2099 was shown to have large elongated columnar grains several millimeters long. Metastable secondary phases, T1 and δ′, were observed and provided strength to the material. Fractography determined fatigue cracks initiate from copper-rich constituent particles. These particles ranged from 1 to 25 μm in size, with an average size of 12 μm. The size of these intermetallic Cu-rich particles influenced the fatigue life of AA2099. Lastly, a microstructure-sensitive fatigue model was used to correlate the various effects of intermetallic particle sizes on the fatigue life of AA2099.

Endurance and Damage in Fatigue of Symmetrical Configuration 2P-2V-2P Perlon-Glass-Acrylic Composite Laminates of Orthopaedic Use

In this paper, an experimental characterization of fatigue behaviour on prismatic specimens of a symmetrical laminated composite material perlon- glass- acrylique 2P-2V-2P for orthopaedic use is conducted. Cyclic repeated solicitation is employed corresponding to applied minimum stress σmin equal zero. The various loading levels imposed on the specimens are 80%, 70%, 60%, 55%, 45%, 35% and 25% of the value of the static failure strength measured in flexure. A significant scatter characterizes the results of material fatigue lifetime. That is the consequence of the heterogeneity of the material structure. The scattered phenomenon prevents any prediction of the lifetime with a good probability using Wohler equation. This enables defining a constant degradation rate by 10% cycle decade. The microstructure morphology study through microscopic observations is also discussed and analyzed. The damage state in fatigue is characterized by a combination of density and orientation of micro-cracks. This damage is mainly due to mechanisms complexity of matrix micro-cracking, inter facial exfoliation, debonding and delamination. The damage evolution stages in the case of cyclic loading have the same nature than those found in static loading but have different chronology and scale.

Fatigue Performance of 2017-T4 AL. alloy Under sub-zero Temperature by Using Electromechanical Freezing System

The effects of sub-zero(-22Co) cyclic rotating bending on the S-N behavior and cumulative damage are reported for 207-T4 aluminum alloy .Experimental characterization of fatigue behavior showed that the S-N curves behavior may described by the following Basquin's formulas: σ_f=1230〖(N_f)〗^(-0.15) At room temperature (RT) And σ_f=1563〖(N_f)〗^(-0.17) At sub-zero temperature (-22Co) From the above equation, the fatigue behavior can be change at σ_f=204 MPa and N_f=159475 cycles . Slightly increase in fatigue life results above 204 MPa and slightly decrease in fatigue below the 204 MPa stress level. A non-linear experimental law is introduced for the accumulation of damage at sub-zero temperature variable fatigue. This law gave conservative and safe fatigue life time prediction when applying to the data of variable fatigue at low temperature (-22 Co).

Fatigue Behavior Characterization of Bituminous Mixtures Made with Reclaimed Asphalt Pavement and Steel Slag

The paper discusses the results of a laboratory evaluation and a theoretical study on the fatigue behaviour of bituminous mixtures with Reclaimed Asphalt Pavement aggregate and electric arc furnace steel slag, used in different proportion.The experimental investigation was performed with the four-point bending test. The fatigue life has been evaluated by three different approaches, based on the 50% reduction of the initial stiffness modulus, the dissipated energy and the damage accumulation.With respect to the reference mixture, composed by a natural aggregate skeleton, the bituminous mixtures with RAP aggregate and steel slag have presented improved fatigue properties and performance.

Material deformation and fatigue behavior characterization for elastomeric component life predictions

AbstractFailure analysis and prediction of fatigue life of elastomers are important issues due to wide usage of elastomeric components in many applications. Material deformation and fatigue characterization including both crack nucleation and crack growth are typically required for such analysis and predictions. This article discusses relevant material deformation properties obtained from experiments conducted under stress states of simple tension and planar tension. Cyclic transient behavior including Mullin's effect is also discussed. Then, fatigue crack initiation approach and experimental procedure and obtained data are discussed including modeling of the R ratio effect. Finally, based on the fracture mechanics approach, fatigue crack growth test procedure and properties are presented, including a model for R‐ratio effect. It is also shown that using the crack growth approach as a total fatigue life predictor gives reasonable results, as compared with the crack nucleation approach. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

FATIGUE BEHAVIOR CHARACTERIZATION OF NITINOL FOR PERIPHERAL STENTS

Nitinol stents are nowadays widely used for the treatment of occlusions in peripheral arteries. However, the expansion of this indication has also highlighted some complications. In particular, the patient daily activities expose the peripheral arteries to large and cyclic deformations which may cause long-term failure of the device and consequently re-occlusion of the artery. Accordingly, the assessment of the stent fatigue rupture is of primary importance to assure the effectiveness of stenting procedure. However the fatigue behavior characterization of Nitinol for peripheral stent is a quite difficult problem because of the complexity of the in vivo solicitations the stent is subjected to and the strong nonlinearity in the material response. In this paper we approached the problem in two steps: (i) in the first step the study of the stent solicitations under realistic (physiological) conditions was performed through the use of numerical simulations which allowed sophisticated patient-specific models of the stenting procedure; (ii) in the second step, the previous results were used for the design of an experimental campaign and the following execution of the tests for the material mechanical characterization and fatigue life study. The tests were performed on Nitinol specimens derived from the same tubes used for producing a commercial peripheral stent and created following the same procedure employed for the device. As a consequence of the small dimension of the specimens, a preliminary design of the experimental test set-up was also required. The obtained results allowed a sufficiently accurate characterization of the stent material fatigue behavior in the range of interest.

Energy Based Characterization of Fatigue Behaviour of Cyclically Unstable Materials

The paper presents a definition of a new energy based parameter which allows to better describe fatigue proprieties of materials, especially cyclically unstable materials in comparison with the Lagoda-Macha parameter. The proposed parameter distinguishes positive and negative work of external force and depends on the sign of the stresses in paths of strain in materials. It is used in laboratory tests for control of a fatigue process on hydraulic stand. A close-loop control system has been equipped with computer program based on MATLAB/Simulink module.

Characterization of fatigue behavior of long fiber reinforced thermoplastic (LFT) composites

Fatigue behavior of long fiber reinforced thermoplastic composites (polypropylene/20 vol.% E-glass fiber) is presented in terms of stress – number of cycles to failure curves. Samples tested along longitudinal direction showed a higher fatigue life than the transverse samples which can be explained by the preferential orientation of the fibers along the longitudinal direction developed during the processing. Fatigue life decreased with increase in frequency. Hysteretic loss and temperature rise were measured; they depended on the stress amplitude as well as the cyclic frequency. Long fiber reinforced thermoplastic composite showed a lower temperature rise compared to unreinforced PP because long fiber reinforced thermoplastic has higher thermal conductivity than unreinforced PP and thus faster heat dissipation to the surroundings occur. The hysteretic heating also led to decrease in the modulus of long fiber reinforced thermoplastic as a function of number of cycles due to the softening of the matrix during fatigue cycling and depended on stress amplitude and frequency of the test.

Fatigue crack growth of filled rubber under constant and variable amplitude loading conditions

ABSTRACTService conditions experienced by rubber components often involve cyclic loads which are more complex than a constant amplitude loading history. Consequently, a model is needed for relating the results of constant amplitude characterization of fatigue behaviour to the effects of variable amplitude loading signals. The issue is explored here via fatigue crack growth experiments on pure shear specimens conducted in order to evaluate the applicability of a linear crack growth model equivalent to Miner's linear damage rule. This model equates the crack growth rate for a variable amplitude signal to the sum of the constant amplitude crack growth rates associated with each individual cycle. The variable amplitude signals were selected to show the effects of R‐ratio (ratio of minimum to maximum energy release rate), load level, load sequence, and dwell periods on crack growth rates. In order to distinguish the effects of strain crystallization on crack growth behaviour, two filled rubber compounds were included: one that strain crystallizes, natural rubber, and one that does not, styrene‐butadiene rubber. The linear crack growth model was found to be applicable in most cases, but a dwell effect was observed that is not accounted for by the model.

Fatigue behavior and FEM modeling of thin-coated components

Physical vapor deposition (PVD) surface coatings make it possible to increase the surface hardness of treated components. Despite the good wear resistance of such coatings, the fatigue behavior of the bulk material may be affected by changes in the residual stress field and microhardness. The two-fold aim of this paper is to characterize the fatigue behavior of thin-coated components and to develop a model for fatigue life prediction. The fatigue behavior characterization was carried out by means of four-point bending tests, while the microstructure of the bulk and coating materials was evaluated by means of SEM analysis, microhardness and residual stress measurements. Equipment with which to carry out the four-point bending tests was specially designed for the purpose. Numerical FEM models of the specimens used in the experimental tests were developed with the aim of giving the designer a useful tool with which to predict the fatigue behavior of thin-coated components. Experimental tests carried out on duplex stainless steel coated with CrN PVD coating (5 μm thickness) validate the numerical model.

Fatigue behavior characterization of laser-welded cold rolled sheet metal (SPCEN)

For the present work, the fatigue behavior of laser-welded cold-rolled sheet metal (SPCEN) was studied. Also, the thickness heterogeneity effect of weldment on the fatigue strength and crack growth behavior was studied. The sheet metals of same thickness (0.9 mm) were laser-welded (Case A), and the sheet metal of 0.9 mm thickness was laser-welded to the sheet metal of 2.0 mm thickness (Case B). For both cases, fatigue tests were conducted applying the load perpendicular or parallel to the welding line. Finite element analysis was performed to determine the form of stress intensity factor as a function of crack length for both cases. The results showed that the fatigue strength of Case A was 8.5% higher than that of Case B when the loading direction was parallel to the welding line. However, the fatigue strength of Case A was similar to that of Case B for the perpendicular fatigue loading to the welding line. At the same crack length, the stress intensity factor of Case A was greater than that of Case B. It was also found that for both cases, the crack propagation rate decreased noticeably in the front of weld bead but increased rapidly in the weld bead. The retardation of crack propagation was due to the increased hardness in the front of weld bead, and the increased crack propagation rate was due to the reduced fracture toughness in the weld bead.

Characterization of Fatigue Behavior of Bonded Composite Repairs

Composite patches are bonded to a cracked metallic surface either symmetrically (double sided ) or unsymmetrically (single sided ) to extend service life. The stresses in the metallic panel are greatly affected by the repair symmetry. Unsymmetric repairs present the greatest challenge because of the presence of out-of-plane bending. Thermal residual stresses are present because of the thermal coefe cient mismatch of the patch and the aluminum plate. Debonding along an adhesive ‐adherend interface can reduce the patch effectiveness. A simple analysis with Mindlin plate theory is investigated to model the host and the repair plate. The two plates are connected by an adhesive layer modeled by effective springs. Large dee ection theory is used in the case of unsymmetric repairs. The springs are ineffective in the debond zone and are removed. Both the aluminum and the debond cracks are characterizedbyfracturemechanicsby useofthestressintensity factorand strain-energyreleaserate,respectively. Experiments on aluminum 2024-T3 plate, AS4/3501-6 carbon/epoxy composite patch and FM73 adhesive include determining the thermal residual stresses in the aluminum plate and observation of debond development by use of an ultrasonic C-scan. Tests are conducted to examine the metallic and debond crack growth interaction on unsymmetric repairs.

Characterization of Fatigue Behavior in Cross-Ply Laminate of SCS-6/Ti-15-3 Metal Matrix Composite at Elevated Temperature

A study was conducted to investigate the fatigue behavior of a cross-ply, [0/90]2s, laminate of silicon fiber reinforced titanium matrix composite, SCS-6/Ti-15-3 at an elevated temperature of 427°C. Two sets of tests, at frequencies 0.02 and 2 Hz, were run at different stress levels. Fatigue damage initiation and growth patterns were dependent on the specific test conditions of frequency and stress level. Microscopic analysis of the fatigued specimens revealed matrix failure mechanisms ranging from ductile failure to cleavage fracture. The results of this study showed that temperature and frequency, as well as stress levels, are important design considerations for this composite in fatigue loading applications.

Characterization of Fatigue Behavior in Quasi-Isotropic Laminate of Ceramic Composite

Fatigue damage mechanisms in a quasi-isotropic laminate, [0/ 2 45/90] s of silicon carbide fiber reinforced calcium-alumino-silicate glass ceramic composite was investigated. Several tests were conducted at different maximum stress levels which intro duced varying degree of initial matrix cracking in 90°, 45° and 0° plies. The initial damage and change in modulus was monitored during the fatigue cycling. Specimens with a considerable amount of initial cracking in 0° plies failed in less than 700 cycles, and others did not fail over one million cycles. The results of this study confirmed the findings of the previous studies regarding the existence of fatigue limit in ceramic composites. The fatigue limit did not correspond to the proportional limit of the static test as reported in the previous studies, however, it corresponded to the initial damage or static loading condition where 0° plies were largely intact.

Fatigue Behavior of Composite Laminate

The paper discusses a characterization of fatigue behavior of [0/±45/90] s glass/epoxy laminate in terms of the following parameters: static properties; S-N relationship; reliability; effect of thickness variation; damage initiation and growth; temperature increase; secant modulus change; effect of preloading on residual modulus and strength; and effect of ply failure on compression buckling strength. Some of the findings are the following. The primary failure process responsible for up to about 106 cycles of fatigue life is the wear-out followed by the chance failure. Change of secant modulus can be used as a measure of damage extent. Preloading to a high level has negligible effect on the residual tensile strength when the fatigue stress is low. However, ply failure and partial delamination result in a moderate loss of compression buckling strength.