Composites containing NiTi shape memory alloy (SMA) long-fiber, short-fibers or Ti long-fiber in a Polycarbonate (PC) matrix have been fabricated by the injection molding technique. Also, prestrained SMA long-fiber/Epoxy matrix composites have been fabricated. The fracture behavior and thermo-mechanical deformation behavior are examined; (1) Fracture behavior – uniaxial tensile tests up to fracture for SMA long-fiber and short-fiber composite (SMAC). (2) Thermomechanical deformation behavior – tensile loading–unloading tests for Pseudoelastic (PE) long-fiber/PC matrix composites. Several thermo-mechanical loading tests for Shape Memory Effect (SME) long-fiber/PC matrix and SME long-fiber/Epoxy matrix composites were used. The obtained results are as follows: (1) The stress–strain relation up to the final fracture of the Shape Memory Alloy Composites (SMACs) showed the repeated up-and-down of the stress which corresponds to the necking of the specimen, fiber fracture, and matrix fracture. The strain for the initiation of necking and the strain for the fiber or matrix fracture in the SMACs were higher than those in the Ti composite. This is attributed to the unique stress–strain relations accompanied by the stress-induced martensitic transformation of the SMA fibers. (2) The SMAC containing PE fiber and PC exhibited the pseudoelastic-like deformation under tensile loading–unloading. (3) The SMAC containing SME fiber and PC exhibited the large contraction by heating after tensile loading–unloading, but the compressive residual stress in the matrix expected in this process was not remarkable. However, compressive residual stress in the matrix may become greater by embedding prestrained fiber in the matrix.
In recent years, some researchers have studied about shape memory alloy composites (SMACs) which consist of a shape memory alloy (SMA) reinforcement and polymer or metal matrix. In particular, considerable attention has been paid to the creation of internal stress in a matrix of SMAC. Internal stress in a matrix can be created when a deformed SMA fiber recovers its original shape in a composite. On the other hand, deformation of the composite appears when internal stress is created in matrix. Therefore, an interaction exists between the creation of internal stress in the matrix and deformation of the composite. The main purpose of the present research is to investigate the effect of fiber volume fraction and aspect ratio (l/d: length divided by diameter of fiber) on the creation of internal stress in the matrix and deformation for a short-fiber SMA reinforced composite (S-SMAC) under thermal loadings. In the present paper, a constitutive relation of S-SMAC is proposed on the basis of the shear-lag model. Then, the effects of fiber volume fraction and aspect ratio on the creation of internal stress in the matrix and deformation of the composite are investigated by using the proposed constitutive relation for S-SMAC under thermal loadings. The main conclusions are as follows: composite shrinkage and compressive residual stress in the matrix increase with increasing aspect ratio and fiber volume fraction after heating. Also, the composite strain history and residual stress history in the matrix are different according to the fiber volume fraction and aspect ratio during heating. The change of aspect ratio has a small effect on the creation of internal stress in the matrix and deformation of the composite. The performances of S-SMAC come close to that of long-fiber SMA reinforced composite (L-SMAC) when the aspect ratio is >25. Also, residual stresses in the fiber and matrix before heating influence the creation of internal stress in the matrix and deformation of the composite during heating.
The present study investigated a novel milling method for producing amorphous rice starch without adding water. A new type of milling machine was developed (termed the shear and heat milling machine (SHMM)), which is capable of applying mechanical shear and heat during the milling process. The SHMM consisted of a pair of rice mortars attached to a servomotor and a ring heater. The heater was installed on the upper mortar; the temperature of the upper mortar was monitored and controlled by a thermal controller. Wide-angle X-ray diffraction (WAXD) analysis was used to determine the crystallinities of starch in rice flour samples produced using the SHMM at different milling temperatures. The WAXD data for milled rice flour that had been heated exhibited no diffraction peaks. This experimental result demonstrates that the developed SHMM produces amorphous rice starch easily by milling with heating without the addition of water. The milling conditions such as the shear and heat applied can be used to control the crystallinity of starch in rice.Abbreviations: SHMM, shear and heat milling machine; WAXD, wide-angle X-ray diffraction.
The aim of the present study is to investigate the local strain band behavior in conjunction with the texture of NiTi thin sheets under mechanical loading. Firstly, we evaluate the transformation temperature by differential scanning calorimetry (DSC) and the internal structure by transmission electron microscopy (TEM) for NiTi thin sheets. Next, we investigate the texture by the x-ray diffraction method for two NiTi thin sheets with different textures. Then, we measure the local strain distribution arising in NiTi thin sheets under uniaxial tensile loading. Finally, we discuss the 'mechanism of angle, nucleation and propagation for local strain band' and the 'relationship between the macroscopic stress-strain curve and local strain band behavior' on the basis of results in the present study.
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