Effect of Temperature Sensitivity and Inelastic Behavior of Phase Materials on the Bearing Capacity of Plane Structures with Uniformly Stressed Reinforcement

An inelastic problem of uniformly stressed reinforcement of plane temperature-sensitive composite structures is formulated. Analytical solutions are obtained for the thermoelastic and inelastic cases. On the basis of these solutions, it is shown that the bearing capacity for inelastic projects can be increased severalfold as compared to thermoelastic projects, and reinforcement can be substantially saved in the inelastic case under fixed loading. Despite the worsening of strength characteristics of the composition phases, the bearing capacity of the structure remains almost unchanged upon heating in the inelastic case and can even increase in the thermoelastic case.     

木粉的酯化改性

在适当的条件下，用ＳＯ＿２－二乙胺（ＤＥＡ）－二甲亚砜（ＤＭＳＯ）处理木材并进行酯化改性，可使木材纤维素完全消晶，软化点（Ｔ＿３）下降到２６０℃左右，形变率达７０％，热稳定性变差，压片的脆性较大；如果用多聚甲醛（ＰＭＯ）－ＤＭＳＯ处理并进行酯化改性，木材的Ｔ＿３大约为１８０℃，形变率为４０％，热稳定性无明显变化，压片的韧性较好。两种酯化木材经热塑成型后都能得到半透明的塑性压片。     

Equal-Stress Reinforcement of Elastoplastic Momentless Shells with a Protective Coating under Thermal and Force Loadings

The problem of equal-stress reinforcement of three-layered momentless shells with fibers of constant cross section under thermoelastic and thermoplastic deformation of phase materials is formulated. A qualitative analysis of systems of resolving equations is carried out. Analytical solutions to the axisymmetric problems of equal-stress reinforcement of shells of revolution under elastic and inelastic deformation are constructed. It is shown that the problem can have several alternative solutions, which can be additionally controlled by varying the reinforcement intensities on the shell contour.     

Improvement of thermoplasticity for s‐BPDA/PDA by copolymerization and blend with novel asymmetric BPDA‐based polyimides

Asymmetric biphenyl type polyimides (PI) derived from 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (a‐BPDA) and p‐phenylenediamine (PDA) or 4,4′‐oxydianiline (ODA) show higher T_gs, and much better thermoplasticity than the corresponding isomeric PIs from symmetric 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA). In addition, a‐BPDA‐derived PIs are completely amorphous owing to their bent chain structures and highly distorted conformations, whereas the PIs from s‐BPDA are semicrystalline. a‐BPDA‐derived PIs possessing these properties or the a‐BPDA monomer were used as a flexible blend component or a comonomer to improve the insufficient thermoplasticity of semirigid s‐BPDA/PDA homo polymer. The blends composed of s‐BPDA/PDA (80%) with a‐BPDA‐derived PIs (20%), as well as the s‐BPDA/PDA‐based copolymer containing 20% a‐BPDA, showed a certain extent of thermoplasticity above the T_gs without causing a decrease in T_g. In addition, these blends and copolymer provided comparatively low thermal expansion coefficient (ca. 18 ppm). The improved film properties for the blends are related to good blend miscibility. On the other hand, when s‐BPDA/ODA was used as a flexible matrix polymer instead of a‐BPDA‐derived PIs, the 80/20 blend film annealed at 400°C exhibited no prominent softening at the T_g. This result arises from annealing‐induced crystallization of the flexible s‐BPDA/ODA component. Thus, these results revealed that a‐BPDA‐derived PIs are promising candidates as matrix polymers for semirigid s‐BPDA/PDA for the present purpose. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2499–2511, 1999     

Thermoelastoplastic Stress-Strain State of Rectangular Plates

A technique is proposed to solve a thermoplastic problem for rectangular plates of varying thickness with arbitrary boundary conditions at all edges. The technique is based on the hypothesis of rectilinear element, the theory of simple loading, and the method of complete systems __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 10, pp. 53–63, October 2005.