MLOLET - Machine Learning Optimized Load and Endurance Testing: An industrial experience report

Dynamic frequency-dependent fatigue damage in metals: A state-of-the-art review

In order to improve reliability of an automotive engine, a fatigue design method was studied based on the fatigue mechanisms in flake graphite cast iron. In the present study, fatigue test specimens were cut from an actual engine component. The material used showed nonlinear behavior in stress–strain relationship from lower stress level during tensile testing. Rotating bending fatigue testing and axial load fatigue testing were performed. Fatigue crack initiation and propagation behavior were observed during the fatigue tests by a replication technique. Fatigue cracking initiated from the tip of flake graphite in early stage of the total fatigue life when the applied stress was higher than the fatigue limit. On the other hand, fatigue cracking was not observed in the specimen tested with applied stress below the fatigue limit. The threshold stress intensity factor obtained with a small surface crack was lower than that obtained with a through-thickness crack. Fatigue limits under various loading conditions such as bending loading and axial loading were predicted well based on fracture mechanics using the $$ \sqrt {\text{area}} $$ parameter. Threshold stress intensity factor for a small surface crack and the maximum graphite size assumed as an initial crack were used for the prediction. Axial load fatigue tests with different stress ratios were performed. The fatigue limit diagram obtained by the fatigue tests did not follow the modified Goodman relation. On the other hand, fatigue limits prediction based on fracture mechanics approach showed good agreement with fatigue limit obtained with fatigue tests in a wider range of mean stresses σmean varying from − 150 to 50 MPa, in negative stress ratio. In case of σmean higher than 50 MPa, in a positive stress ratio, a smaller effect of stress ratio in the fatigue limit diagram was observed. It was considered that this phenomenon could be explained by the lower effect on the crack closure in a small surface crack initiated from the tip of graphite flake and also influence of local plastic behavior of the matrix around the tip of graphite flake. It can be summarized that the fracture mechanics approach is an effective way to predict fatigue limits of an engine component produced by flake cast iron in different loading conditions and in wider range of mean stress conditions.

Staircase testing is a standard method for evaluating the fatigue strength of components. However, staircase testing assumes a normal distribution, while components can display bimodal behavior due to flaws in material, or issues during the manufacturing process. Three unique step loading data sets on different production crankshafts provide evidence that step loading reliably identifies material or manufacturing issues, which lower a component's fatigue strength. Staircase testing has an 87% or greater chance of overestimating the component's fatigue strength, which in turn overestimates the component's expected reliability. For example, a component with a 99.9% reliability based on staircase testing would only have a 74% reliability based on step loading. If a component contains an undetectable manufacturing defect, staircase testing has a 99% chance of overestimating the component's fatigue strength. Step loading reliably improves the estimation of a component's fatigue strength distribution while providing insights into a component's defect tolerance.

Defect-based fatigue crack nucleation and strength evaluation of additively manufactured TiC/Ti6Al4V titanium matrix composite at different temperatures

Aluminum carbody for rolling stock is light and easily recycled, but includes severe defects which are very dangerous to fatigue strength. Strength evaluation of a carbody by static load test has been performed. However, true evaluation of fatigue strength could not be performed because fatigue failure is caused by dynamic alternating loads. In this study, to evaluate fatigue strength of the aluminum carbody of urban transit unit, a large scale testing method to simulate actual dynamic loads is proposed and the fatigue failures of the carbody are investigated. The test results are compared with the estimated results by static load test and structural analysis. Also, the differences between the results are discussed. The compared results show that flexural response of the carbody plays a significant role in occurrence of fatigue failure. The estimation of fatigue failure based on static load test or static analysis may provide misleading results. It was also verified that the fatigue life characteristics of the aluminum carbody can be estimated from the published fatigue test data for aluminum components with similar joint detail. Test and evaluation of fatigue strength based on the established static load test method needs to be modified to consider dynamic response of the carbody.

Fatigue life prediction method for AISI 316 stainless steel under variable-amplitude loading considering low-amplitude loading below the endurance limit in the ultrahigh cycle regime

Fatigue fractured surface of component wire for steel wire ropes : Ueda, K. and Fujinaka, Y.J. Min. Mater. Process, Inst. Jpn. Jan. 1990 106, (1), 29–33 (in Japanese)

Mechanical performance of a hybrid zirconia developed through hydrothermal treatment and Room-Temperature Atomic Layer Deposition (RT-ALD)

Evaluation of full thread screw and different fixation configurations in Pauwels type III femoral neck fracture

Oxidative stress in chronic obstructive pulmonary disease patients submitted to a rehabilitation program

Cyclic-to-monotonic loading tests and fatigue damage tests were conducted to reveal the deformation characteristics and mechanical properties of argillaceous quartz siltstone under cyclic loading. When the upper limit loading was changed from less than to greater than the fatigue strength, both the axial and lateral cumulative residual strains extended from a monotonically increasing convex curve to a concave curve. The hysteresis loop distance evolved from sparse-dense to sparse-dense-sparse. The residual strain rate and relative area of hysteresis loop was changed from L-shaped to U-shaped. The elastic modulus evolved from three stages of initial rapid rise, decline, and slow and steady development to monotonically decreasing concave curve to convex curve. The lateral-to-axial strain ratio was changed from a monotonically decreasing concave curve to a monotonically increasing convex curve, and then extended to a concave curve. With the increase of the upper limit loading, the rock compressive strength of the argillaceous quartz siltstone was first increased and then decreased after cyclic loading of 3000 times. The maximum value was 13.62% higher than the uniaxial compressive strength. When the upper limit loading was less than the uniaxial elastic limit, the rock compressive strength after the cyclic loading was slightly less than the uniaxial compressive strength. When fatigue failure occurred, the relation between the fatigue life and the upper limit loading exhibited a power function distribution. The fatigue strength was approximately 80%~89% of the uniaxial compressive strength. With the increase of the upper limit loading, the elastic modulus first increased and then decreased, while the lateral-to-axial strain ratio continually increased. The weak structural fracture effect and the compaction effect under cyclic loading on rock are proposed, which can explain the strength characteristics and mechanical parameters evolution law of porous weak cemented rock under cyclic loading.

Fatigue tests were conducted on smoothed specimens of a carbon steel, S35C, under repeated two-step loadings as well as constant amplitude stresses, and the probabilistic characteristics of fatigue lives under varying loading conditions were examined by considering the both relations of stress-plastic strain and of plastic strain-fatigue life.The main results obtained are as follows; (1) The distribution of fatigue lives was found to be represented by log-normal distributions for both constant stress amplitude and repeated two-step loading tests. (2) Although fatigue lives under the constant stress amplitude tests showed a fairly large scatter at a stress level near the fatigue limit, those under the varying loading tests did not show such a large scatter at that level and a slightly increasing tendency of the standard deviation of fatigue life with the increase of fatigue life was found in the region below the fatigue limit. (3) Little correlation was found between the variances of the stress-plastic strain relation and of the plastic strain-fatigue life relation for the varying loading tests, and it was found that the variance of the former relation was very much smaller than that of the latter one. Therefore, the variance of the stress-fatigue life relation for the varying loading tests of a particular load pattern was concluded to be determined by the variance of the plastic strain-fatigue life relation.

The 30 MJ, 10 MW superconducting magnetic energy storage (SMES) system was devised to interact in the Western US Power System as an alternate means to damp unstable oscillations at 0.35 Hz on the Pacific HVAC Intertie. The SMES unit was installed at the Tacoma Substation of the Bonneville Power Administration (BPA). The operating limits of the 30 MJ SMES unit were established, and different means of controlling real and reactive power were tested. The unit can follow a sinusoidal power demand signal with an amplitude of up to 8.6 MW with the converter working in a 12 pulse mode. When the converter operates in the constant VAR mode, a time varying real power demand signal of up to 5 MW can be met. Experiments showed that the Pacific ac Intertie has current and reactive power variations of the same frequency as the modulating frequency of the SMES device. Endurance tests were run to assess the reliability of the SMES subsystems with a narrow band noise input, which is characteristic of the modulation signal for stabilizer operation. During the endurance tests, parameters of the ac power system were determined. Converter short circuit tests, load tests under various control conditions, dcmore » breaker tests for coil current interruption, and converter failure mode tests were conducted. The experimental operation of the SMES system was concluded and the operation was terminated in early 1984.« less

Muscle endurance and cervical electromyographic activity during submaximal efforts in women with and without migraine

Asphalt Mixture Fatigue Testing: Influence of Test Type and Specimen Size