This paper overviews state of the art of multiaxial low cycle fatigue. Many review papers have already published on multiaxial low cycle fatigue and most of the review papers discuss correlation parameters of multiaxial low cycle fatigue lives by categorizing the parameters. This paper, however, rather focuses on the physical background of the effect of multiaxial stresses and strains on low cycle fatigue lives. Firstly, little effect of mean stress (hydrostatic stress) on tensile stress-strain relationships was presented to discuss little effect of the mean stress on crack initiation lives in multiaxial low cycle fatigue. Next, competing two cracking modes, maximum shear and principal cracking modes are discussed. The two cracking modes complexly occurred in multiaxial low cycle fatigue, depending on strain range, strain multiaxiality and existence of notches. At the third part of this paper, couples of energy and strain parameters developed by the authors were introduced and discussed for the correlation of multiaxial low cycle fatigue lives, and those parameters were compared to examine the difference of the parameters. Nonproportional low cycle fatigue lives were discussed in relation with the additional hardening of materials at the last of the paper.
In order to control the surface mechanics of a metallic material, mechanical treatment of the surface, such as by shot peening, water jet peening, cavitation peening or laser peening, is often done. In this review paper, we discuss the mechanical properties of such treated surfaces and the effect of the treatment on fatigue strength. Although there is a detrimental increase in surface roughness introduced by the various treatments, the positive effects, such as the introduction of compressive residual stress and/or work hardening, i.e., an increase in the yield stress, outweigh the negative effects, then treatments improve the fatigue strength. The compressive residual stress introduced by the various treatments is closely related to the crack closure and crack initiation. If the same peening process is used, the fatigue strength can be estimated from the residual stress distribution. However, when the mechanical surface treatments were different, the residual stress distribution of the specimen at the same fatigue strength was totally different. Namely, when different peening processes are applied to the surface, the compressive residual stress only shows a tendency to improve the fatigue strength, and the fatigue strength cannot be evaluated precisely from the residual stress distribution, Thus, a fatigue test is required to evaluate the fatigue strength. As the fatigue strength strongly depend on the crack initiation, an evaluation of the threshold level of the stress intensity factor range of a treated surface is valuable, and it can be possible by a plate bending fatigue test using a notched specimen.
This review of previous studies on the damage and mechanical modelling of fibre-reinforced composite materials, especially carbon-fibre-reinforced plastic composites, is based on the findings of recent studies conducted in conjunction with other researchers. Studies that utilized various modelling scales, ranging from macroscopic to microscopic, are considered. The modelling of impact damage, ply cracks, ultimate tensile failure, the initiation of transverse ply cracks, the micro-mechanical properties of interfaces and molecular dynamics are specifically addressed. In addition, the scope for future work in the field is described.
The current modular design has been established on the basis of engineering knowledge and concerns for the traditional machine tool, which has the limited machining function. With the growing importance of the machining function-integrated machine tool, we need to establish a new “ Raison d'être ” of the modular design, and a symptom is the “ Platform Concept ”. This paper reviews first the present perspective for the “ Platform Concept ” after quickly noting the modular design at present. The paper conceptualizes then a “ Platform-based Unit Construction ”, i.e., a variant of the new modular design, discusses its leading applications possible, and suggests a handful of research and engineering development subjects to establish it.
This paper reviews the transmission of high frequency broadband ultrasound via a thin layer in contact with a solid. A large part of this article deals with the physics of the acoustic resonance in a material system comprising water, a thin layer and a solid. Generally, it is very difficult to maintain the continuity between the layer and the solid during transmission of the ultrasound. The dry-contact ultrasonic technique, where the air at the layer/solid interface has been evacuated, enables the transmission of high frequency broadband ultrasound via the interface and allows us to realize acoustic imaging without the sample getting wet. In this case, to realize high-resolution acoustic imaging of a solid sample, selection of the layer to be inserted is important, and the acoustic resonance phenomenon is used for this purpose. The dry-contact and conventional ultrasonic techniques and their respective inspection capabilities are compared in this article. Moreover, the acoustic resonance phenomenon is used to characterize layered media. The acoustic properties of a thin polymer film, i.e., the acoustic impedance, ultrasonic velocity and density, can be accurately determined, and any scattering sources, e.g., voids, etc., can be detected with high sensitivity using this technique. The thicknesses of coatings on both surfaces of a steel plate can also be precisely measured by observing the acoustic resonance phenomenon occurring in the ultrasonic transmission system.
This paper reviews the material models of cyclic plasticity in which memory surfaces are used to extend isotropic hardening. Focus is given to strain-range-dependent cyclic hardening and workhardening stagnation; the former is noticeable even at small strains, while the latter is evident at large strains and is thus considered one of the factors of accurate springback analysis. Because strain-range-dependent cyclic hardening and workhardening stagnation cannot be properly simulated by taking accumulated plastic strain as a measure of isotropic hardening, material models of cyclic plasticity have been proposed using memory surfaces to extend isotropic hardening. Material models developed in this way are reviewed, along with experimental observations.
This paper discusses what has been found and what will be found using conceptual “origami” models to develop deployable space structures. The study covers the following: (i) one-dimensional structural elements, which are axially buckled inflatable tubes; (ii) two-dimensional elements, which are deployable membranes, such as solar arrays and solar sails; and (iii) deployable elements in nature. The study clarifies what design considerations are necessary to adapt the basic concepts to actual space structural hardware, and several limitations of origami models are discussed. Regarding the last subject, this study envisions future space structures using conceptual origami models that imitate three-dimensional deployable structures in nature, such as flowers and insect wings.