Fatigue Residual Strength Research Articles

Experimental investigation on shear fatigue behavior of perfobond strip connectors made of high strength steel and ultra-high performance concrete

This paper explores the fatigue performance of perfobond strip connectors (PBL) made from high-strength steel (HSS) and ultra-high performance concrete (UHPC) by fabricating and testing eight push-out specimens. The failure modes, load-slip curves, stiffness degradation, and residual strength of the PBLs are presented and discussed. The experimental results show that fatigue loads caused connector’s crack formation and stiffness degradation, leading to concrete dowel shear fracture and transeverse rebar bending-shear rupture damage. Compared to the static performance, the fatigue residual strength of the PBL subjected to 0.5 × 106, 1.25 × 106, and 2.0 × 106 loading cycles decreases by 1.2 %, 3.6 %, and 14.5 %, respectively, with corresponding reductions in ductility of 14.7 %, 19.4 %, and 4.7 %. Under the same loading cycles, the fatigue residual strength and ductility of the PBL with a maximum repeated load of 0.65Pu are 13.0 % and 3.9 %, respectively, smaller than those of 0.55Pu. A semi-empirical model based on the elastic foundation beam theory and linear cumulative damage model is developed to predict the residual strength of the PBLs using HSS and UHPC. The accuracy and applicability of the model are calibrated using the experimental results. The findings of this study can serve as an experimental foundation and theoretical reference for the fatigue design of PBLs made with high-strength materials.

Residual Stress and Fatigue Strength Analysis of Stiffener Welds of Steel-Plate Composite Girder Bridge Considering Welding Sequence

Residual Stress and Fatigue Strength Analysis of Stiffener Welds of Steel-Plate Composite Girder Bridge Considering Welding Sequence

Fatigue performance analysis of precast segmental assembled concrete beams

In recent years, assembled bridges have become widely utilized in bridge construction, raising concerns about durability-related bridge diseases over time. These issues significantly impact the fatigue life of assembled bridges, necessitating an in-depth exploration of their fatigue performance. While existing research primarily concentrates on the transverse connection of multiple longitudinal beams, there is a notable dearth of studies on longitudinal precast segmental assembled bridges. This paper addresses this gap by establishing a fatigue benchmark finite element model for segmental assembled concrete beams, building upon existing experiments. The study employs numerical simulation to analyze the entire fatigue process, examining stress distribution, damage development, and considering the influence of reinforcement corrosion. Furthermore, a fatigue life prediction method, based on fatigue residual strength (R), is proposed for predicting the fatigue life (N) of concrete in precast segmental assembled beams. Results reveal that prestressed and ordinary reinforcements experience increasing stress with loading cycles, peaking around 100,000 cycles. Throughout fatigue loading, compressive stress in concrete remains low, preventing fatigue compression failure. However, tensile stress near joints gradually rises, initiating cracks at the mid-span beam’s bottom. With continued cyclic loading, these cracks propagate towards the loading point. The upper and lower limits of fatigue life predicted by the fatigue life prediction method closely align with the compressive fatigue test values of concrete, proposed fatigue life prediction method is efficient and accurate.

Study on the Residual Strength of Nonlinear Fatigue-Damaged Pipeline Structures

The heat alternation and bending during the service process of the pipeline structure are the key issues affecting its residual strength. The nonuniform plastic deformation of its cross-section causes nonlinear damage to the structure, which makes it difficult to calculate the residual strength of the overall structure. This study proposed a novel variable-strength material damage model with damage accumulation, which achieved the coupling analysis of structural damage and material fatigue residual strength, making the structural strength of nonlinear damage cross-section computable. Based on this, a theoretical ultimate load model for nonlinear damage cross-section and a finite element analysis model for dynamic material strength with damage accumulation were established. The analysis was conducted on the repeated banding damage to coiled tubing. The results showed that the residual yield strength of nonlinear damaged coiled tubing showed a trend of first rapid decrease and then slow decrease with damage accumulation, and the tensile displacement showed an increasing trend with damage accumulation. The ultimate internal pressure strength of nonlinear damaged structures showed a similar downward trend to the yield strength. The nonlinear damage coupling analysis model proposed in this study has significant practical engineering application value.

Residual stress, fatigue behavior, and mechanical properties of equal-channel angular pressed commercial pure titanium

Residual stresses, fatigue behavior, and mechanical properties of equal channel angular pressing (ECAP) commercial pure titanium (CP–Ti) are investigated in this study. Residual stresses can significantly affect the performance and reliability of CP-Ti components under cyclic loading conditions. The study focuses on understanding the relationship between ECAP processing, residual stresses, and fatigue behavior in CP-Ti. The ECAP process was employed to produce CP-Ti grade 2 samples, and their fatigue behavior was characterized. The results revealed a significant increment in residual stresses, fatigue strength, microhardness, and tensile strength by ECAP processing on the CP-Ti. The measured fatigue limit of the processed CP-Ti was found to be higher than that of coarse-grained CP-Ti and approaches the fatigue limit of the Ti–6Al–4V alloy. Residual stresses resulting from non-conventional machining processes and surface treatments are known to affect the fatigue life of titanium alloys. Compressive residual stresses have been shown to inhibit the growth rate of fatigue cracks and improve fatigue life. Understanding the effect of residual stresses on the fatigue behavior and mechanical properties of ECAP-processed CP-Ti is crucial to optimizing the design and ensuring the long-term durability of CP-Ti components in engineering applications.

Analyzing the macroscopic/mesoscopic mechanical properties and fatigue damage of graphene oxide/microcapsule self-healing concrete

Concrete materials used in transmission projects in Northwest China require specific properties, such as crack resistance, fatigue resistance, and low impedance. To meet these requirements, microcapsules with repair properties were synthesized using a physical method. Graphene oxide was employed as a conductive medium and reinforcing material to prepare standard concrete composite parts. Furthermore, the stress state and cracking behavior of the microcapsules in concrete were simulated through the Python-based secondary development of ABAQUS. An orthogonal test design was conducted to determine the optimal graphene oxide, microcapsule, and water–cement ratios. Based on the orthogonal test results, fatigue testing was conducted to assess the fatigue strength, fatigue life, and crack development behavior of the concrete under combined dynamic and static loading. The results show that the thickness of the microcapsule wall material directly influences the fracture extension and practicability of the concrete. Including a certain amount of graphene oxide can enhance the strength of the concrete, reduce its resistivity, and compensate for the microcapsule-induced early strength loss. The optimal graphene oxide/microencapsulated concrete ratios were determined as 3 % microcapsule admixture, 0.1 % graphene oxide admixture, and 0.45 water–cement ratio. Notably, at low stress levels, graphene oxide and microcapsules act synergistically to enhance concrete fatigue resistance. Graphene oxide/microencapsulated concrete exhibits higher residual fatigue strength than ordinary concrete; however, the difference in their fatigue resistance diminishes as the number of cycles increases.

Residual Stress Relaxation Behaviors and Fatigue Strength of Micro-Shot Peened EA4T Axle Steel under Constant and Variable Loading

Residual Stress Relaxation Behaviors and Fatigue Strength of Micro-Shot Peened EA4T Axle Steel under Constant and Variable Loading

Effect of galvanostatic anodic polarization on hydrogen evolution rate and residual fatigue strength of Mg alloys for implant use

For surgery, biodegradable magnesium alloys are considered promising candidates. The low corrosion resistance is advantageous since the implant is degraded in the presence of aqueous body fluids, supporting the human bone for a defined time and be fully degraded after this functional phase, making a second surgery for implant removal unnecessary. To design this phase and prevent early implant failure, precise knowledge of the degradation behavior over months and the correlating mechanical stability is essential. In vitro tests of the required duration are associated with enormous time and cost efforts. Therefore, a short-time method is developed to accelerate the degradation progress by anodic polarization without affecting the corrosion mechanism. The method is based on the corrosion behavior of Mg alloys under polarization, accompanied by increasing hydrogen evolution for increasing current densities, allowing conclusions to be drawn about the corrosion rate. Three-week immersion tests of the alloy WE43 with and without plasma electrolytic oxidation are the starting point. The time-dependent corrosion rates are to be reproduced by applying anodic polarization within three days. An experimentally determined relationship between current density and corrosion rate is used to design the polarization. The corrosion morphology of both testing strategies is analyzed by µCT. To evaluate the influence of the morphology on the mechanical stability, ex situ multiple amplitude tests are performed, allowing an estimation of the residual fatigue strength. The results show that a qualitative simulation of the hydrogen evolution rate is possible by applying polarization, achieving an enormous time saving. Due to a changed corrosion morphology with increased pitting tendency and the associated reduced residual fatigue strength, the method has to be considered as a worst-case evaluation allowing to exclude unsuitable Mg-based biomaterials right from the beginning, in particular before further preclinical studies.

Study on the Causes of Highway Pavement Cracks in Desert Environment

According to relevant statistics, more than 90% of domestic high-grade asphalt pavement is semi-rigid base pavement, and semi-rigid base cracking is a congenital stubborn disease and common. In Tengger Desert section of Wuma expressway, the temperature difference is large, and the cracking of temperature shrinkage and dry shrinkage is difficult to avoid, resulting in the decline of pavement structure strength. Once the semi-rigid base is cracked, the asphalt pavement is equivalent to a flexible structure; the residual fatigue strength is greatly reduced; the long-term service performance of pavement structure can not be guaranteed; the durability is poor, the damage layer is deep; the repair is difficult and the cycle is long; maintenance costs are relatively high. This paper analyzes the causes of pavement cracks in the harsh environment in the hinterland of Tengger Desert, and studies its mechanism and treatment scheme.

Fatigue performance of rib-to-deck joints in orthotropic steel deck with PWHT

Post-weld heat treatment (PWHT) displays potential for enhancing the fatigue strength of rib-to-deck (RD) welded joints in orthotropic steel decks (OSDs) by mitigating welding residual stress. In this study, residual stress measurements, fatigue tests, and fracture analyses were performed to investigate the influence of PWHT on the welding residual stress and fatigue strength of RD joints. Eighteen full-scale specimens were fabricated, i.e. ten PWHT-processed specimens and eight as-welded specimens without additional treatment. Hole drill (HD) and X-ray diffraction (XRD) were used to measure the residual stress in four PWHT specimens and four as-welded specimens. The PWHT specimen showed a reduction in the peak residual stress by 76% and 78% in the HD and XRD results, respectively. Fatigue tests were carried out on the six PWHT specimens and four as-welded specimens. The comparison was made between the two specimen types using the mean value of equivalent fatigue strength derived at 2 million cycles. The results indicated that PWHT improved the mean equivalent fatigue strength of RD joints by 23% and 33% under nominal stress and hot-spot stress, respectively. Parametric investigations were carried out using finite element-based fracture analysis to elucidate the influence of residual stress mitigation on fatigue crack growth in RD joints. The result indicated a significant decrease in the crack growth rate owing to residual stress mitigation. Such a decrease enhances the fatigue strength of RD joints.

Research on the Residual Bearing Capacity of a Rib Beam Bridge Carriageway Slab Based on Fatigue Cumulative Damage

In order to study the residual bearing capacity of the carriageway slab of a reinforced concrete rib beam bridge after fatigue damage, a double T-beam carriageway slab model with a high degree of symmetry was designed and fatigue tests were carried out. Based on the fatigue cumulative damage theory, the fatigue residual strength equation of concrete was improved and a constitutive fatigue model of a steel bar and concrete with arbitrary loading times was established. Because the carriageway slabs are highly symmetrical, we used a ratio of length to width and a ratio of width to height to express the dimensional changes in the carriageway slabs. Abaqus general analysis program was used to create a symmetrical T-beams model and analyze the influence of the fatigue load level, the ratio of width to height of the roadway slab, and the ratio of length to width on the remaining bearing capacity of the roadway slab. Finally, the 1stOpt fitting software was employed to fit the roadway slab’s residual bearing capacity evaluation model. The fatigue test results show that the fatigue failure form of the roadway slab is punching failure, and the development law of fatigue damage can be divided into three stages, accounting for 6.25%, 56.25%, and 37.5% of the total fatigue life. The finite element analysis results showed that the length–width ratio of the roadway slab is positively correlated with its relative residual bearing capacity, and the residual bearing capacity of the two-way slab is higher than that of the one-way slab. The fatigue load level and the aspect ratio of width to height are negatively correlated with their relative residual bearing capacity.

Residual stress and fatigue strength of longitudinal attachment joints improved by HFMI treatment under static load

Residual stress and fatigue strength of longitudinal attachment joints improved by HFMI treatment under static load

Impact of the drilling process on the surface integrity and residual fatigue strength of 2024-T351 aluminum parts

This paper investigates the influence of the drilling process on an aluminum 2024-T351 part in terms of surface integrity and fatigue strength. Two drilling processes (axial; orbital) are considered. The surface integrity is studied through surface roughness measurements, microstructure and hardening analysis and residual stress assessment. An innovative Hole Opening Comparative Technique is set up to assess the residual stress state. Fatigue tests are conducted with open-hole specimens, and on filled-hole samples (double-lap bearing strength tests). The strain hardening of the hole subsurface seems to be the main factor influencing the fatigue behavior, associated with a residual stress state.

Experimental Study of the Probabilistic Fatigue Residual Strength of a Carbon Fiber-Reinforced Polymer Matrix Composite

Degradation of the mechanical properties of fiber-reinforced polymer matrix composites (PMCs) subjected to cyclic loading is crucial to the long-term load-carrying capability of PMC structures in practice. This paper reports the experimental study of fatigue residual tensile strength and its probabilistic distribution in a carbon fiber-reinforced PMC laminate made of unidirectional (UD) carbon-fiber/epoxy prepregs (Hexcel T2G190/F263) with the ply layup [0/±45/90]S after certain cycles of cyclic loading. The residual tensile strengths of the PMC laminates after cyclic loading of 1 (quasistatic), 2000, and 10,000 cycles were determined. Statistical analysis of the experimental data shows that the fatigue residual tensile strength of the PMC laminate follows a two-parameter Weibull distribution model with the credibility ≥ 95%. With increasing fatigue cycles, the mean value of the fatigue residual strength of the PMC specimens decreased while its deviation increased. A free-edge stress model is further adopted to explain the fatigue failure initiation of the composite laminate. The present experimental study is valuable for understanding the fatigue durability of PMC laminates as well as reliable design and performance prediction of composite structures.

Effects of Conventional and Severe Shot Peening on Residual Stress and Fatigue Strength of Steel AISI 1060 and Residual Stress Relaxation Due to Fatigue Loading: Experimental and Numerical Simulation

This study investigates and compares the effects of different shot peening treatments including conventional and severe shot peening on microstructure, mechanical properties, fatigue behavior, and residual stress relaxation of AISI 1060 steel. Shot peening treatments were applied with two Almen intensities of 17 and 21 A and a wide ranges of coverage (100%–1500%). Various microstructural observations were carried out to analyze the evolution of microstructure. Microhardness, residual stress and surface roughness measurements and also axial fatigue test were performed. Moreover, the extent of the residual stress relaxation during cyclic loading was investigated by means of XRD measurements. Furthermore, numerical simulation of residual stress relaxation due to fatigue loading was carried out and validated against experimental investigations. The comparison indicated a good agreement for the surface residual stress relaxation up to 100 cycles. The experimental results indicated the efficiency of severe shot peening processes in obtaining nanostructured surface layer and achieving superior mechanical properties and fatigue behavior. Also, residual stress measurements revealed that stress relaxation started with a high rate at the initial stages of loading and gradually increased at higher number of cycles which was lower in the case of severely shot peened samples compared to the conventionally treated ones.Graphic

Fatigue response of a solid state self-healing resin

The present work verified the capability of a solid state self-healing system for retarding or arresting fatigue cracks in epoxy materials subjected to cyclic loading at room temperature. A solid state self-healing material is demonstrated using a thermosetting epoxy polymer which was modified by incorporating a linear thermoplastic polydiglycidyl ether bisphenol-A (PDGEBA) as a healing agent. The stress-controlled constant amplitude (CA) tensile fatigue behavior at stress ratio, R = 0.1 and frequency 10 Hz for both the neat and the modified epoxy was investigated. Fatigue life and residual strength degradation were continuously monitored during the fatigue tests. The modified epoxy fatigue life was shown to be increased by ∼50% after healing periods. The fatigue-healing process was proven through the surface and cross-section resin morphology analyses using microscopy optic and scanning electron microscope (SEM). On the whole, the solid state self-healing system has proven to be very effective in obstructing fatigue crack propagation, effectively improved the self-healing polymeric material to achieve higher endurance limits.

Effect of Ultrasonic Surface Impact on the Fatigue Properties of Ti3Zr2Sn3Mo25Nb.

The effect of nano grain surface layer generated by ultrasonic impact on the fatigue behaviors of a titanium alloy Ti3Zr2Sn3Mo25Nb (TLM) was investigated. Three vibration strike-numbers of 24,000 times, 36,000 times and 48,000 times per unit are chosen to treat the surface of TLM specimens. Nanocrystals with an average size of 30 nm are generated. The dislocation motion plays an important role in the transformation of nanograins. Ultrasonic surface impact improves the mechanical properties of TLM, such as hardness, surface residual stress, tensile strength and fatigue strength. More vibration strike numbers will cause a higher enhancement. With a vibration strike number of 48,000 times per square millimeter the rotating-bending fatigue strength of TLM at 107 cycles is improved by 23.7%. All the fatigue cracks initiate from the surface of untreated specimens, while inner cracks appear after the fatigue life of 106 cycles with the ultrasonic surface impact. The crystal slip in the crack initiation zone is the main way of growth for microcracks. Crack cores are usually formed at the junction of crystals. The stress intensity factor of TLM titanium alloy is approximately 7.0 MPa·m1/2.

Comparison of biomechanical properties of cervical paravertebral foramen screws, lateral mass screws and pedicle screws

Objective To investigate and compare the biomechanical strength of paravertebral foramen screws (PVFS), lateral mass screws (LMS) and pedicle screws (PS). Methods A total of 30 human cervical spine vertebrae (C3-C6) were harvested from 8 fresh-frozen cadaver specimens whose mean age was 45.3±11.2 years at death. The vertebrae were randomly divided into three groups for specific screws. For each vertebra, one side was randomly chosen for direct pullout strength test (speed 5 mm/s), and the other side for fatigue test (displacement ±1.0 mm, frequency 1 Hz, 500 cycles) and residual pullout strength test. 4.5 mm × 12 mm screws were used for PVFS, 3.5 mm × 14 mm screws for LMS, and 3.5 mm × 24 mm screws for PS. Results The direct pullout strength was 327.10±17.07 N for PVFS, 305.71 ± 11.63 N for LMS, and 635.67 ± 22.82 N for PS. The residual pullout strength was 265.62 ±18.19 N for PVFS, 192.80 ±17.10 N for LMS, and 494.89 ±41.79 N for PS. The residual pullout strength of PVFS, LMS and PS respectively, compared with the direct pullout strength, decreased by 18.8%, 36.93% and 22.15% (tPVFS=7.795, tLMS=17.267, tPS=9.349, P<0.001). The direct pullout strength of PS was higher than that of PVFS and LMS(t=34.245, t=40.741, P< 0.001), as well as PVFS was slightly higher than LMS (t=3.275, P=0.004). The residual pullout strength of PS was the highest, PVFS was the second, and LMS was the smallest (F=314.619, P<0.001). For the fatigue test, the load at the first cycle and the first time when the set position was reached of PVFS were higher than those of LMS (t=3.625, P=0.002; t=5.388, P<0.001) and PS (t=2.575, P=0.019; t=2.680, P=0.015), but there was no difference between those of LMS and PS (t=0.609, P=0.550; t=1.953, P=0.067). The load at the last cycle of PVFS and PS was higher than that of LMS (t=5.341, P<0.001; t=3.439, P=0.003), while there was no difference between PVFS and PS (t=1.606, P=0.126). Conclusion The direct pullout strength of PVFS was slightly higher than that of LMS, and the residual pullout strength was significantly higher than LMS. The property of fatigue resistance of PVFS was similar to PS and obviously better than LMS. In summary, PVFS can be used as an effective substitute for LMS and PS. Key words: Cervical vertebrae; Spinal fusion; Bone screws; Biomechanics

Effects of Laser Marking on Fatigue Strength of Titanium Alloys

Abstract Laser marking is a requirement for all medical implants in the biomedical industry. The purpose is to provide permanent identification of the details of an implant, such as the part number, size, lot number, etc., in the form of laser engraving. The intent of this practice is mainly to provide the information needed to correctly identify an implant when removed from its package and before its use and, secondly, to provide the necessary information when an implant is surgically removed from a patient’s body to analyze the cause of removal. However, laser marking can affect the fatigue performance of an implant and create a heat-affected zone, though other factors, such as the positioning of the marking along with the laser marking parameters, can also play a significant role. The improper choice of laser marking parameters can induce high residual stresses on the implant. High tensile residual stresses can result in fracture at the marking region, and hence, compressive or low tensile residual stresses are desired. Therefore, the objective of this study was to evaluate the effect of various laser marking parameters on the residual stresses and fatigue strength of titanium alloy. Laser marking parameters, such as power and pulse speed, were varied and residual stresses were calculated using the X-ray diffraction technique. Heat-affected zones were imaged using a digital microscope. Finally, four-point bend tests were conducted to evaluate the fatigue strength for samples with different laser parameters. The results from the testing demonstrated that laser parameters can have a significant impact on the tensile or compressive residual stresses. Laser-marked samples also showed a reduction in fatigue strength as compared to non–laser-marked samples.

Fatigue stress analysis of the DV-2 engine turbine disk

Purpose The purpose of this study is to improve life prediction of certain components. Fatigue of the high-stressed structural elements is an essential parameter that affects the lifetime of such components. In particular, aviation engines are devices whose failure due to fatigue failure of one of the important components can lead to fatal consequences. Design/methodology/approach In this study, two analyses in the turbine disk of the jet engine during the simulated operating load were performed: The first one was the analysis of the heat-induced stresses using the finite element method. The goal of the second analysis was to determine the residual fatigue strength of a loaded disk by the software tool using the Palmgren - Miner Linear Damage Theory. Findings The results showed a high degree of similarity with the real tests performed on the aircraft engine and revealed the weak points in the design of the jet engine. Research limitations/implications It should be mentioned that without appropriate experiments, results of this analysis could not be verified. Practical implications These results are helpful in the re-designing of the jet engines to increase their technical feasibility. Originality/value Such analysis has been realized in the DV-2 jet engine research and development program for the first time in the history of jet engine manufacturing process in Slovakia and countries of Eastern Europe region.