Key Engineering Materials Vols. 452-453

Abstract: Recently, permanent magnet motors are widely used in wide industrial fields because they are suitable for compact mechanical system. The motor core is usually manufactured from magnetic steel sheet with press machine. However, usually most parts of the plate are scalped, and only small percent of the sheet is used for the core. The spiral accumulating core system is suitable for manufacturing the core more ecologically because in this system more than 50% of the magnet steel sheet can be used. In this study, therefore, the effective Young’s modulus of the spiral accumulating core is considered in order to find out a good method to fix the core. In this analysis, effective Young’s modulus of spiral accumulating core used for permanent magnet motor is considered by the application of the finite element method to 3D models, whose layers and slits are periodically arranged. Then, effects of slits, layers and embossing interlockings on effective Young’s modulus are analyzed. Finally, a convenient method of calculation based on rule of mixture is newly proposed for estimating the effective Young’s modulus of the real spiral accumulating core.

Abstract: Steel conveying rollers used in hot rolling mills must be exchanged very frequently at great cost because hot conveyed strips induce wear on the surface of roller in short periods. In this study, new roller structure is considered which has a ceramics sleeve connected with two short steel shafts at both ends by shrink fitting. Here, the ceramics sleeve may provide longer life and reduces the cost for the maintenance. However, sometimes the steel shaft has to be pulled out for exchange. Simply, heating outside surface and cooling inside surface of the shaft are necessary for separation. However, attention should be paid to the maximum thermal stress of the ceramics sleeve in the process of separation. In this paper, finite element method analysis is applied to the structure and thermal stress has been calculated with the varying dimensions of the structure. Also several effects on thermal stress have been investigated, such as the effect of shrink fitting ratio, outside diameter, the fitted length, thickness of shaft, materials an so on. Finally the most appropriate thermal conditions to reduce maximum stress and make separation easy have been discussed, which is very useful for designing of new rollers.

Abstract: Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with a single edge interface crack as well as a double edge interface crack in a bonded plate. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stresses at the crack tip calculated by the finite element method. Then, the stress intensity factors are indicated in charts under arbitrary material combinations. Specifically, some necessary skills as refined mesh and extrapolations of the stress intensity factors are used to improve the accuracy of the calculation. It has been proved that the values shown in this paper have at least 3-digit accuracy. For the edge interface crack, it is found that the dimensionless stress intensity factors are not always finite depending on Dunders’ parameters , . For example, they are infinite when . And they are finite when , and zero when .

Abstract: Adhesive joints are widely used as the joints with the same or different adherents, such as in engineering and electric devices. However, because of mismatch of different materials properties, failures due to crack initiation and propagation are often observed on the interface between adhesive and adherents. Therefore, it is important to analyze stress intensity factor of crack on the interface. In this paper, the effect of material combination of adhesive and adherents on stress intensity factor and effect of the thickness of adhesive on stress intensity factor are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stresses at the crack tip calculated by finite element method. The stress intensity factors are indicated in charts under different thickness of adhesive . It is found that the intensity of singular stress first increases with increasing , then decreases from about , and keeps constant from about , when is the width of adhesive. These results are helpful to design dimensions of devices and choose appropriate materials when adhesives are used inside of them.

Abstract: Laminated copper films of the epoxy-bonded or diffusion-bonded to the base metal were used in order to investigate and analyze film fatigue behavior depending on the inevitable bonding interfaces for electric/functional parts used in MEMS. Fatigue damage was observed using SEM and crack initiation lives were evaluated at the notch root where the bonding interfaces could be observed directly through the thickness. These observations showed that the resin interface layer caused cracks without slips in a zig-zig pattern and also decreased fatigue crack initiation lives. On the other hand, fatigue damage was observed using an optical microscope on surface of the film with resin bonding or with diffusion bonded interfaces. In this case, many cracks were caused and propagated towards the width direction on the film bonded to the base steel with resin, while slip and cracks were caused along slip lines during fatigue on the film bonded to the base steel by diffusion. There was a significant difference in crack initiation behavior of the films between resin and diffusion bonded to base metals. This finding was not only for crack initiation site but also for roughness near the crack on the film. Using Eulerian equation of motion in continuum, this difference was discussed in terms of elastic displacement field with a wave caused from the base plate subjected to cyclic deformation. Such a wave motion enables us to understand the geometric effects of bonding interfaces on the fatigue damage behavior of the bonded film to base metal.

Abstract: Set out from a basic idea that damage is a course of energy dissipation, a new damage variable is present. The damage variable is obtained for arbitrary strain state of soil according to the superimposing principle of compatible probability event for volumetric strain and shear strain. Through the analysis of a series of triaxial experimental results of structured soil, a new damage evaluation equation is put forward. The computation results tally with the experimental data show it is reasonable that this new damage variable and its evaluation law for structured soil.

Abstract: In this study, molding condition and tensile properties of jute fiber reinforced composite were examined. PVA resin was used as matrix which is one of the biodegradable resin. Before tensile test, specimens have an offset twist. The tensile test after twist of jute fiber cloth was also conducted. As a result, following results were obtained. In the case of jute fiber cloth, the effect of twist deformation to tensile strength is not great. The reason is thought that the fiber cloth is flexible and easy to deform in this form. In the case of composite, molding time has an effect to the tensile properties. As the molding temperature increases, the tensile strength increases. So, the diffraction intensity was measured. The reason of effect to the strength is thought that the crystallization occurred in the matrix. When the molding temperature is so high, fiber has degradation, and the strength of the composite decreases. As the degree of twist increases, the strength decreases. The reasons are the delamination between layers and debonding between fiber and matrix.

Abstract: Cylindrical specimens of Inconel 713LC in as-cast condition and with Al diffusion coating by the CVD technique were cyclically strained under total strain control at 800 °C. Hardening/softening curves, cyclic stress-strain curves, and fatigue life curves are obtained. The coating has a beneficial effect on the Manson-Coffin curve while the fatigue life is reduced in the Basquin representation. The stress response of the coated material is lower in comparison with the uncoated one. Sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.

Abstract: Q345qC steel is widely used in corrugated steel web. In this paper, the fatigue strength of Q345qC steel between 105~109 cycles was investigated using the ultrasonic fatigue testing technique, with a loading frequency of 20 kHz. The fracture surfaces of specimens were observed with scanning electron microscopy (SEM). The experimental results show that the S-N curve of Q345qC steel continues to decrease with the increase of the number of cycles between 105 and 109 cycles and does not generally exhibit a plateau beyond 107 cycles. The observation of fracture surface shows that the mechanism of fatigue failure is similar in both case of ultrasonic fatigue and conventional fatigue in long life regime. Cracks initiate from a mass defect of specimen surface or an interior inclusion.

Abstract: The problem of dynamic stress intensity factor is investigated theoretically in present paper for a radial crack on a circular cavity in an infinite piezoelectric medium, which is subjected to time-harmonic incident anti-plane shearing. First, a pair of electromechanically coupled Green’s functions are constructed which indicate the basic solutions for a semi-infinite piezoelectric medium with a semi-circular cavity. Second, based on the crack-division technique and conjunction technique, integral equations for the unknown stresses’ solution on the conjunction surface is established, which are related to the dynamic stress intensity factor at the crack tip. Third, the analytical expression on dynamic stress intensity factor at the crack tip is obtained. At last, some calculating cases are plotted to show how the frequencies of incident wave, the piezoelectric characteristic parameters of the material and the geometry of the crack and the circular cavity influence upon the dynamic stress intensity factors. While some of the calculating results are compared with the same situation about a straight crack and with static solutions.