Language：Japanese   Publisher：The Society of Materials Science, Japan  

Probabilistic properties associated with residual life against fatigue failure under random overloads with retardation phenomenon are investigated through computer simulations, where ductile fracture mode is simultaneously taken into analysis. First, based upon a fatigue crack growth model under plural overloads proposed by one of the authors, a system of random differential equations is formulated under random overloads. Next, the so-called reset function, which describes a size of a newly created yielding zone near crack tip by an overload, is newly proposed for steel materials. Based upon the bi-modal approach for failure occurrence against random overloads, in which both a fatigue failure mode and a ductile failure mode are taken into account, the residual life distribution for each failure mode is numerically estimated through computer simulations. Finally, residual life probability distribution function of a cracked component is numerically shown under two failure modes.

DOI： 10.2472/jsms.74.359

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Other Link： https://ndlsearch.ndl.go.jp/books/R000000004-I034226573

Language：Japanese   Publisher：The Society of Materials Science, Japan  

This study investigates optimal maintenance analysis against fatigue failure based upon computer simulation approach with a new probabilistic model using a random field. Probabilistic models reported so far often face difficulties in accurately representing the variability in fatigue crack growth resistance and encounter computational problems in analytical approaches. Our model, having been introduced in earlier works, addresses these issues by generating fatigue crack growth samples through computer simulations, thereby facilitating practical applications to practical maintenance problems.In this paper, this model is applied to derive and analyze history-independent optimal maintenance strategies, focusing on three key factors: material inhomogeneity, crack detection variability in inspections, and uncertainty on initial crack lengths in virgin components. Numerical examples demonstrate that (i) the inspection time interval gradually decreases as the number of inspections increases as well as having been qualitatively pointed out and (ii) the proposed method using the new probabilistic model can derive optimal maintenance strategies even under increased model complexity and uncertain factors.

DOI： 10.2472/jsms.74.365

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Other Link： https://ndlsearch.ndl.go.jp/books/R000000004-I034226595

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

A simplified probabilistic model is newly developed to give equivalent description for a strengthening method using two-layer CFRP plates bonded to base components by adhesion. First, a system of simultaneous differential equations for the shear and vertical stresses acting on the adhesives are derived. In order to reflect the variation of debonding, it is extended to a system of random differential equations by considering the spatially random variations of the adhesive thickness. Then, in order to reduce the degree of freedom of the system for two-layer CFRP plates, a one-layer equivalent model is newly developed to give almost equivalent result on the probabilistic properties associated with debonding of adhesives in two-layer model, where equivalency is achieved from two points of view; one is a mechanical condition and the other is a fine adjustment on probabilistic factors. Finally, numerical examples are shown to validate the proposed equivalent model, in which Monte Carlo method is applied to estimate the probability of debonding. The results indicate that the proposed model can give appropriate estimation for the probability of debonding, only with reasonably reduced computing efforts.

DOI： 10.1299/mej.24-00316

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-23K11000/

Language：Japanese   Publisher：The Society of Materials Science, Japan  

A probabilistic model is newly proposed for describing random deterioration of pumping wells, in consideration of application to efficient management of pumping wells using a concept of asset management procedure. First, introducing a health index for quantifying specific capacity, we formulate a differential equation describing mean deterioration of the helth index. Next, it is extended to a random differential equation, in which a Gaussian white noise is introduced for representing intensive fluctuation around the mean deterioration behavior, so that intensively random variation of the health index can be well reproduced. A probability distribution of the health index is then derived in an analytical form. Finally, the obtained probability distribution is compared with actual data of the health index for active eight pumping wells in Joyo area, Kyoto prefecture, Japan. It is clarified that the scatter of health index of actual pumping wells is quite well reproduced by the theoretically derived probability distribution from the newly proposed probabilistic model.

DOI： 10.2472/jsms.72.168

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Language：Japanese   Publisher：The Society of Materials Science, Japan  

Statistical estimations for probability distributions having tails of special shape, such as a double-mode distri-bution as well as the so-called heavy-tailed or fat-tailed distribution, are quantitatively discussed through virtual experiments using computer simulations. In this paper, a probability distribution describing the damage degree of concrete liners of tunnels in cold region is examined as an example of the double-mode probability distribution. First, virtual data sets of observations are generated by the use of quasi-random numbers for a Pareto distribution as a typical example of the fat-tailed distribution, whereas the actual data set obtained for the damage degree of concrete liners is used for generating virtual data set for the double-mode distribution. Next, statistical estimations are executed by the use of probability papers to identify the probability distribution showing the “best” fitting among supposed plural candidates for probability distributions. Finally, the accuracy of the estimation is quantified by applying the coefficient of determination. The results show that the accuracy of the estimation in the tail region is scarcely improved even if the number of data is increased.

DOI： 10.2472/jsms.72.174

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