The purpose of the present article is to provide a perspective for a network model for glassy polymers and computational predictions of mechanical behavior related to plastic instabilities, such as neck and shear band formation, and their propagation. The constitutive equations developed using the molecular chain network theory are discussed. The computational strategy for the simulation, and neck and shear band propagations in plane strain and under 3D conditions with and without thermomechanically coupled conditions are presented with illustrative examples.
One of the antimicrobial alkoxysilanes, 3-(trimethoxysilyl) propyl dimethyl octadecyl ammonium chloride (TMSAC), was applied to the sol-gel reaction to prepare the antimicrobial wood-inorganic composites from tetraethoxysilane (TEOS). The obtained TMSAC-SiO2 composites revealed some antimicrobial activities, but the use of the property-enhancer, 2-heptadeca-fluorooctylethyltrimethoxysilane (HFOETMOS) in a small quantity could provide water-repellency to the composites which has, further, improved its activities against both white-rot and brown-rot fungi. In addition, after a prolonged soil burial test, TMSAC woods have lost antimicrobial properties, whereas the TMSAC-SiO2, particularly, HFOETMOS-(TMSAC-SiO2) composites could have its high activities maintained. Therefore, it may be concluded that HFOETMOS-(TMSAC-SiO2) and TMSAC-SiO2 composites can provide sustainably high antimicrobial properties in wood.
An investigation work was made on the influence of the piercing process on the rotary forging effects, redundant shear deformations and power consumption. In this work, a study was made to compare the double and single piercing process with reference to the Mannesmann piercing mill and the cone-type piercing mill developed by the authors. If the conventional double piercing process employing the Mannesmann piercing mill is replaced by the single piercing process employing the cone-type piercing mill, the rotary forging effects and redundant shear deformations can be inhibited, and then, the materials with poor workability, such as stainless and high alloy steel can be pierced without inside bore defects. Furthermore, from the viewpoints of the piercing power and power consumption, the single piercing process employing the cone-type piercing mill is very economical. As a result, the single piercing process employing the cone-type piercing mill provides the best economical advantage with respect to both capital and running costs.
In addition to the super piercer, “the new super piercer”, which allows expansion piercing, has been developed by the authors. The development of the skewing technology for disc roll axes and its application to the cone-type piercing technology results in a remarkable increase in the expansion ratio. In this paper, studied in detail were the influences of the expansion ratio, feed and cross angles on the rotary forging effects, those on the redundant shear deformations and those on the inside bore defects in materials with poor hot workability. Furthermore, discussed in detail were the influences of the expansion ratio, rotary forging effects and redundant shear deformations on the inside bore defects in materials with poor hot workability. As a result, it has been quantitatively clarified that the rotary forging effects are the major causes of the initiation of inside bore defects, and that the redundant shear deformations are the major causes of the propagation of inside bore defects. Noteworthy is the influence of the expansion ratio. It should be noted that the larger the expansion ratio is, the more remarkably the inside bore defects decrease.
Mode I and mixed mode loading testing of ABS resin were carried out by using compact tension shear specimens. Two types of ABS resin were examined. The first one (ABS-1) has a butadiene rubber content of 18wt% in the form of small particles of diameter of about 200nm. The second one (ABS-2) has the same overall butadiene rubber content but a bimodal particle distribution with diameters of 200nm and 500nm. Crack initiation behavior was observed by using a video microscope. The fracture toughness of ABS-2 obtained by mode I testing is larger than that of ABS-1. The fracture angle for both materials under mixed mode loading coincides with the values predicted by the maximum hoop stress criterion. On the contrary, at crack initiation under mixed mode loading, the critical values of KI and KII are larger than those estimated by the maximum hoop stress criterion. The increase in the critical values of KI and KII under mixed mode loading for ABS-2 is higher than those for ABS-1. The bimodal type distribution of rubber particle size produces better fracture resistance.
Primary creep behaviors of the lamellar structured Ti-46.6Al-1.4Mn-2Mo (at.%) alloy (EPM alloy), which is fabricated by hot extrusion of a blended elemental powder mixture (EPM), are investigated in an air environment over the temperature range of from 775 to 900°C under constant stress ranging from 150 to 250MPa. The apparent activation energy of the primary creep deformation is measured to be increased with the creep strain and found to be saturated to the value of the activation energy of the steady state creep deformation. Reduction of effective stress with creep strain in the primary region is suggested to be responsible for the increase in the apparent activation energy. All the creep rates normalized by the apparent activation energies measured at the given creep strain within the primary region show the stress exponent of 4.2 when plotted against the applied stress.
This paper describes a newly developed analytical method for the evaluation of creep-fatigue strength for stainless weld metal. Based on the observation that creep-fatigue crack initiated adjacent to the interface of σ-phase/δ-ferrite and matrix, a mechanical model, which allowed the evaluation of micro stress/strain concentration adjacent to the interface, was developed. Fatigue and creep damages were evaluated, using the model which described the microstructure after long time exposure to high temperatures. It is concluded that one major scope of this model is to predict analytically long term creep/fatigue life of stainless steel weld metals, the microstructure of which has been degraded as a result of in-service high temperature exposure.
In order to develop a long term creep-fatigue evaluation method of stainless steel weldment, that incorporates the degradation of weld metal, the authors have looked into the mechanism of micro damage in the structure of type 308 and 316 weld metals that had been subjected to thermal and mechanical histories using transmission electron micrography. The results obtained were as follows: 1) Carbide (M23C6) and Laves phase that precipitated in δ-ferrite phase were transformed into σ-phase being more stable at high temperatures after long time heating. 2) While δ-ferrite phase remained in the microstructure at 550°C even after the change of its composition due to the transformation, above 600°C, it disappeared after the complete transformation into σ or austenitic phase. 3) The rate of dissolution of δ-ferrite phase under cyclic stresses for fatigue or creep-fatigue failure was higher than the one under constant stress for creep failure; it was also increased by a factor of 10 to 100 in comparison with an unloaded case. 4) The dissolution of δ-ferrite phase led to initiation and propagation of cracks at the interfaces of σ and remaining δ-ferrite or austenitic phase, causing a difference of mechanical properties between them.
Thick snow or ice adhering to the surface of an antenna used for radio communication can impede telecommunication, so methods to reduce the build-up of snow and ice are needed. We have studied the use of water-repellent coatings to prevent snow and ice sticking, and in this paper, we report our results of tests on ice adhesion and how it is affected by the contact angle, surface roughness and thermodynamics. And we obtained the results as following: (1) A water-repellent coating consisting of PTFE particles dispersed in polyvinylidene fluoride exhibited a contact angle of 150 degrees. (2) Ice adhesion was linearly proportional to the surface free energy of the water-repellent coating. (3) The higher the surface roughness of high wettability materials, the stronger the adhesion. The higher the surface roughness of water-repellent coatings, the weaker the adhesion.