Papers by Keyword: Fatigue

Abstract: Mechanical fatigue is an essential phenomenon that occurs when the structures are exposed to dynamic, fluctuating loadings. Especially automotive components are regularly exposed to random vibration loadings. Vibration fatigue failures may arise even in components that meet static requirements and are stable and robust, because of dynamic and fluctuating loadings. The primary focus of this study is the research of the vibration fatigue. Hence, in addition to the analyses, the tests are conducted. In order to study the analyses and tests, aluminum cross-section beams are designed and manufactured. The notched sections added to the beam geometry to acquire a more distinct fatigue life compared to other parts of the beams. The results obtained from the experimental tests are used to correlate the effect of notch parameters on fatigue life.

Abstract: Shot peening mechanical treatment surface, commonly used to improve material surface mechanical properties, as fatigue and wear resistance increase, induces deformations in the material crystal lattice, characterized by the presence of stress. Additionally, plasma nitriding, another surface treatment used to minimize failures in austenitic stainless steels, can produce resistant surface layers, composed of the interstitial nitrogen atoms accommodated in austenitic structure, increasing the layer hardness. Thus, the present work aims to study the residual stress and layer formation on austenitic stainless steel F138 surface, after different treatment conditions. Plasma nitriding treatment after shot peening differences were analyzed. Residual stress was investigated by X-ray diffraction, using sin²ψ method. Samples of surface morphology and formed layer were analyzed by scanning electron microscopy (SEM) and X-ray diffraction. Previous shot peening treatment to plasma nitriding promotes the formation of a less homogeneous layer, with microcracks and induced residual stress increase. It was observed the formation of iron nitrides and expanded austenite after plasma nitriding treatment. Surface residual stress induction after shot peening and plasma nitriding treatments can be efficient methods to improve material mechanical properties.

Abstract: A single pocket cage is the SKF product, which is used in Large Size Bearings for wind industry. The function of a bearing cage is to hold, guide and separate rolling elements, and differently from the conventional cage, the current one consists of segments, which eases the bearing assembly and reduces its weight. The long life challenge (25 years!) requires considering fatigue, and since the single pocket cage is made of PEEK polymer, it is also susceptible to creep (in near room temperature), which enhances fatigue damage. The current work proposes the numerical model capturing non-linear viscoelasticity of PEEK. The mechanical behavior of this material is identified in uniaxial tension test and is modeled in Finite Elements (FE) by means of the Parallel Rheological Framework (this numerical tool has been recently implemented in the commercial software ABAQUS). The current FE model enables to apply cyclic loading, simulating the material response of cage when it operates in running bearing. By applying sub-modeling technique only a small domain is modeled which improves the computational time efficiency. The sub-model domain corresponds to the cage region, where the stress is high resulting to the material yielding, fatigue/creep degradation (due to inelastic cyclic deformation) and initiation of fatigue crack. The FE results were combined with the test data, in attempt to relate the numerically predicted damage to the cage life. The development of irreversible deformation during cyclic loading, shakedown analysis and the stress volume effect, are the main focuses of the current work.

Abstract: Titanium alloy fasteners are extensively used in advanced fields such as aerospace due to their corrosion resistance, high-temperature endurance, low density, and high strength-to-weight ratio. In practical applications, fatigue failure is the primary failure mode for these fasteners. Besides the operational environment, the manufacturing process, especially surface treatment techniques, plays a crucial role in affecting the fatigue life of titanium alloy fasteners. This paper examines the impact of three surface treatment processes-rolled fillet, pulsed anodization, and molybdenum disulfide coating－on the fatigue life of titanium alloy fasteners through orthogonal experiments. The study finds that both rolled fillet and molybdenum disulfide coating significantly influence the fatigue life. This effect is associated with residual stresses, where compressive residual stress initially increases with rolling pressure but subsequently decreases, and reduces as the thickness of the molybdenum disulfide lubricating film rises.

Abstract: This paper presents a case study of an in-service failure occurred in a pressurized gas supply pipeline, which has been recurring in recent years, particularly during the winter season. The investigation focused on two pipe coupons extracted from a DN 300 pipeline, which had sustained damage while in operation as part of a natural gas pipeline. Through the implementation of mechanical and non-destructive testing methods on the pipe couplings and their welds, multiple non-conformities were identified. These non-conformities were found to be the root causes of failures that occurred after welding and during operation. The findings of this investigation have led to several valuable comments and recommendations, which are beneficial for manufacturing companies and clients alike. Implementing these suggestions can contribute to enhanced safety and operational efficiency in gas pipeline systems.

Abstract: Recently, researchers have developed the method as a harmless the crack by the surface modification. For the purpose of contributing to reliability improvement of the A6061-T6 structure by harmless method, the following research was carried out: The tensile residual stress of friction stir welding was added by shot peening, resulting in a more significant compressive residual stress than that of the base metal. The effect of the surface crack aspect ratio on the maximum harmless crack depth (a_hml) of A6061-T6 was evaluated for residual stress distribution. The detectable depth was evaluated in the relationship between a_hml and the maximum detectable crack depth (a_NDI) by non-destructive inspection (NDI).

Abstract: The purpose of the work is to quantify and predict the influence of inhomogeneity of local properties on the overall behavior of the selected casting aluminum wheel and knuckle in different loading cases. Smooth and notched tensile specimens and torsion specimens are extracted from different positions in the wheel and knuckle and tested. The dependences of the flow stress, the fracture strain, and the S-N curve on position for specimen extraction are evaluated. Metallographic investigations are performed to reveal the relations between microstructure/microdefects and the mentioned properties. A damage model based on a triaxiality-dependent fracture strain is calibrated and used to simulate the specimens and component tests. The simulations of static wheel tests and knuckle fatigue tests are performed with position-dependent material parameters. The prediction of the component tests is compared with the experimental results.

Abstract: The performance of added 50% reclaimed asphalt (RAP) mixtures was investigated by four-point bending fatigue tests (FPBT). Mixtures with 50% RAP were modified with SBS polymer, diatomite (D) and hydrated lime (HL). Ten specimens were produced and fatigue of specimens was evaluated with FPBT. Some samples give the fatigue breaking cycle compatible with each other. In some samples, the number of cycles is much higher than the average breaking load. Some samples may deteriorate in a short time before the end of test. Although the briquettes are mixed homogeneously for longer mixing times and produced with great care, inconsistent results can be obtained. If water damage is applied to briquettes due to the presence of HL, more compatible results can be obtained. The use of SBS-HL and rejuvenating oil at high RAP ratios will provide more compatible results. As a result of 50% stiffness reduction, the difference in the remaining stiffness values is usually 2-3 times, while there are huge differences between the cycle numbers that cause this. In terms of sustainable and long-term performance, the homogeneity of the pavement composition appears to be essential, having a much more pronounced effect than the number of loadings.

Abstract: Anisotropic conductive film (ACF) is frequently used in the packaging manufacture for fine-pitch conductivity and interconnection, maintaining the electrical and mechanical connections between micro-electrodes. A key determinant of good conductivity is the deformation, fatigue, and breakage of conductive particles within the ACF packaging. This study aims to measure the resistance changes of specific conductive channels and observe the microscopic fatigue damage of compressed ACF conductive particles through the fabrication of Flex Printed Circuits (FPC) / Indium Tin Oxide-coated Polycarbonate (ITO-coated PC) specimens and the setup of bending experiments. The results show that the deformation, fatigue, and breakage of conductive particles will quantitatively affect electrical conductivity performance. By microscopically observing the breakage morphology of conductive particles before and after bending, it can be found that bending in the ACF packaging area further exacerbates the previously compressed and broken conductive particles, with cracks continuing to grow and shatter.

Abstract: The aluminum 5754 alloy is one of the widely used engineering materials in shipping, rivet making, tread plates and automotive industries. These engineering structures envisage variable loading conditions during their service. In addition to it, it is also experiencing seismic vibrations. Hence, the engineering components made from such aluminum alloy are susceptible to fatigue fracture. In the current study, the prediction of fatigue crack growth (FCG) in 5754 aluminum alloy was made using the exponential function. The beam specimen comes up with a cross-section of 25X25 mm², a span length of 300 mm with a mechanical notch length of 2.70 mm at the centre was subjected to four-point bending (FPB) employing hydraulic INSTRON 8800 tensile testing apparatus. The periodic loading condition deformed the material up to large plastic deformation. The applied load was further down the elasticity of the material. The experimental data provided the relation between crack length (a) to the number of cycles (N) to failure. The response surface methodology (RSM) and modified exponential equation were used to predict the FCG. In RSM, when “stress intensity factor (K)” and “number of the cycle (N)" were considered independent variables, the response (a) was optimum (maximum) as compared to when “stress intensity factor range (del K)” and “fatigue crack growth rate (da/dN)” were considered independent variables. Hence, for designing the aluminum 5754 alloys as engineering structures, it was the number of cycles which provides a safe design as compared to da/dN. The modified exponential equation using an exponential function predicted the FCG for aluminum 5754 alloy in the form of a beam specimen. The anticipated results agreed with experimental data as the prediction ratio was 1.20 and the % deviation was 3.7.