Papers by Keyword: High Cycle Fatigue

Abstract: The current work investigates the high cycle fatigue behaviour of two aluminium alloys (5754-H22, 6082-T4) under a tensile shear-loading condition joined by clinching methods. Clinching is a rapidly growing technology in the automotive, electronics, and household appliances industries. Several industrial sectors apply this technology to join lightweight materials due to their cost-effective and environmentally friendly characteristics that involve interlocking two (or more) sheets of materials without the need for additional fasteners or adhesives. Clinched joint specimens were prepared using a standard clinching process, ensuring consistent joint geometry and interfacial contact. The joined sheets have been produced in three levels: a similar pair of 5754, a similar pair of 6082, and a combined of 5754-6082, with a bottom thickness of 0.5 mm and a base TOX tool dimension. Subsequently, the high cycle fatigue behaviour of the clinched joints was assessed through cyclic loading tests. The ΔL-N curves were constructed to illustrate the relationship between the number of cycles to failure and the applied load range levels. Both the fatigue and the previous tensile strength tests were conducted with an MTS-type electro-hydraulic materials testing equipment. During the constant load amplitude investigations, the stress ratio was constant (0.1). Furthermore, a sinusoidal loading waveform with a frequency of 30 Hz were applied for the entire test series. Additionally, all tests were carried out at room temperature and in laboratory air. The results from the tests indicated that both the tensile shear and the high cycle fatigue resistance, in other words, both the static and cyclic behaviour of clinched joints were appropriate. In conclusion, this investigation provides valuable insights into the mechanical performance of aluminium alloy clinched joints under both loading conditions. The findings emphasize the importance of joint design optimization for improving durability and reliability in structural applications Results, show that the high cycle fatigue strength of the clinched joints represents competitive fatigue resistance than traditional welding joints.

Abstract: Device reliability is an important factor in application, especially in the field of electric mobility. In this paper high cycle fatigue power cycling results of SiC devices in baseplate free modules are presented. To minimize testing time, the devices were stressed with load pulses corresponding to a 50 Hz load. The reliability results are the first fatigue results for temperature swings below 30 K for SiC devices. The lifetime in the high cycle fatigue area is limited by solder fatigue for high virtual junction temperatures of 150 °C. In theory, the reliability should increase exponential since the elastic-plastic transition area is reached. The experiment revealed that the lifetime can still be described by the Coffin-Manson approach also in the high cycle fatigue area. It can be observed that the high junction temperatures weaken the stability of the solder layer, so no major lifetime increase can develop. The measured temperature data are additionally corrected by a three-dimensional (3D) simulation to ensure a validity of the results.

Abstract: High cycle fatigue (HCF) caused by the vibratory stresses is the main cause of failure in many machine components, e.g. aircraft engine and gas turbine components, which has caused loss of many lives and billions of dollars. To avoid these kind of failures, vibratory stresses should be attenuated to an acceptable level, especially at resonant frequencies. A lot of previous studies have shown that thin coatings of different materials significantly reduced these vibratory stresses by adding extra damping to the system. These include viscoelastic materials, plasma graded coatings, piezoelectric materials, and magneto-mechanical damping material coatings, but some of these had applicability and performance issues. Among these thin coatings, magneto-mechanical materials are very effective in reducing these vibratory stresses significantly.In this study, the effect of different beam structure thicknesses under same magneto-mechanical coating of 0.2mm was studied. For this purpose, Ni₃Al was applied as magneto-mechanical coating. The natural frequencies, damping ratios and displacements of beams were calculated before and after applying magneto-mechanical coatings using forced response analysis and hammer tests. The results indicated a sharp change in vibration characteristics i.e. natural frequency, damping ratio and beam deflections, of all the beams used. The results showed that the magneto-mechanical coatings were more effective when applied to thin structures as compared to thick structures, because thin structures have higher strains, which enabled magneto-mechanical coatings to dissipate larger amounts of energy of applied loadings, because performance of these coatings is strain dependent.

Abstract: This paper presents the residual properties and parameters of the damage-based fatigue life prediction models of the steel wire ropes under fretting fatigue conditions. The damage mechanics-based approach is employed to develop the predictive method for the reliability of the steel wire ropes. The elastic modulus is dependent on the fatigue load condition and the accumulated number of the load cycles. The characteristic degradation of the Young’s modulus of drawn steel wires is established through the phenomenological presentation of the interrupted fatigue test data. The samples are given a quasi-static loading followed by a block cyclic loading with various stress amplitudes and ratios. The residual Young’s modulus is calculated after each block of cycles. The effect of the different loading condition with the amplitude and mean stress on the measured fatigue life of a single wire is presented using the life parameter, χ. The residual Young’s modulus data are presented in terms of normalized quantities. Significant reduction in the elastic modulus due to fatigue is exhibited after enduring 70% of the fatigue life of the material. The fitting constants are obtained, and the fitted equation is used to describe the degradation of Young’s modulus at N number of cycles. Subsequently, the data can be applied to predict the fatigue-life of steel wire ropes and assess its reliability through fretting-induced damage models.

Abstract: In the present paper, two novel methods for determining the fatigue limit are presented. Despite the fact that these methods are different in principle, both represent a new approach to testing where the main benefit is reduced consumption of material. The first method is based on small round specimens and can be considered as one of semi-destructive testing methods. The second method is based on infrared thermographic analysis and requires only one specimen. Results obtained with these techniques were compared with those obtained from standard high-cycle force-controlled fatigue tests under constant loading until failure.

Abstract: The high cycle fatigue behavior of an aluminum alloy of small and large grains was investigated. Samples of small and large grains were provided as rotating bending fatigue test specimens. The samples were tested at eight different stress levels from 103 MPa (15 ksi) to 345 MPa (50 ksi) with a 34 MPa (5 ksi) increase at each level. As-received samples were evaluated for optical microstructural analysis. Scanning electron microscopy (SEM) images were used to evaluate the fractured surface of several samples. High cycle fatigue S-N curves were generated. The fatigue test results showed that grain size has a strong influence on the fatigue life. The high cycle fatigue S-N curves of small grains showed better fatigue life as compared to large grains in the lower stress levels. At higher stresses, the situation was reversed.

Abstract: Retracted article: This paper investigates the effect of a galvanizing coating on the fatigue strength of S355 structural steel. The aim of the present paper is to partially fill this lack of knowledge. A comparison is carried out, between hot dip galvanized fillet welded cruciform joints made by S355 structural steel and not treated welded joints characterized by the same geometry, subjected to a load cycle R = 0. Thirty four new experimental data are summarized in the present contribution, in terms of stress range Δσ and averaged strain energy density range in a control volume of radius R₀ = 0.28 mm.

Abstract: Retracted article: The effect of a galvanizing coating on the fatigue strength of S355 structural steel is analyzed in detail showing that the decrease of the fatigue life is very limited if compared with that of uncoated joints and the results are in good agreement with Eurocode detail category, without substantial reductions. The procedure for the preparation of the specimens is systematically described in this note providing a useful tool for engineers involved in similar practical applications. The results are compared with previous data from notched galvanized specimens weakened by a central hole and not treated specimens characterized by the same geometry.

Abstract: Martensitic high-carbon chromium bearing steel is used for rolling contact applications in various mechanical parts. Induction heating is one of heat treatment methods which take shorter time and lower energy compared with furnace heating. In the present work, we prepared induction-heated and furnace-tempered JIS SUJ2 bearing steel bar specimens. After rotating bending tests, we observed their fracture surfaces. It was found that the very large fisheye crack failures occurred and the crack size increased with increasing number of cycles to failure.

Abstract: The high cycle fatigue response of Ti-45Nb alloy was investigated by using an ultrasonic fatigue testing system. The effect of notch geometry on the fatigue response was studied on samples with different circumferential grooves. The experiments showed a decrease of fatigue notch sensitivity with decreasing the notch radius. Finite element analysis (FEA) was conducted for calculation of the stress distribution in the samples and interpretation of the experimental results. Further, the lifetime of the alloy showed a strong dependency on the location of the defects and microstructural inhomogeneities. It was observed that at the same stress amplitude, early failure was caused by surface defects, while those with a longer lifetime failed due to cracks originating from internal flaws.