The use of the J-integral to investigate fracture characterization in a carbon black reinforced natural rubber is described. Three applications to crack initiation are included: two based on the use of a hypothetical zero specimen length and one on conventional testing procedures for metals. While the validity of the zero-length methods is questionable, the conventional method yielded a consistent Jc value of 1.01 N/mm for a typical tire compound. This value was obtained from 24 combinations of varying specimen geometries and pre-crack lengths. The J-integral is revealed as a valid fracture parameter that is applicable not only for material evaluation but also for designing tire structures to resist premature failure. These conclusions disagree with those from an earlier investigation, so the causes for the discrepancies are examined and discussed.

The paper presents an investigation of the interaction between a macroscopic crack and distributed damage in an elastic-plastic material based on the HRR field model for virgin materials. This is achieved by describing the mechanical effects of the distributed micro-cracks in terms of the damage variable D on the HRR fields. Damage evolution equation and the constitutive equations coupled with damage are formulated and the resulting boundary value problems are solved numerically. Material constants ~, n and mo are varied to examine their effects on the resulting stress distributions. It is found that the HRR fields for damaged and virgin materials are surprisingly similar although the severity of damage equivalent stress is of several orders of magnitude higher than the conventional plastic equivalent stress without damage consideration. Furthermore, it is shown theoretically and justified numerically that the J-integral loses its path independency for damaged materials, causing the amplitude of the singularity Ko to remain an unknown variable in the asymptotic analysis.

The structure and design method of an electric drive system for high power applications are presented. A multiphase permanent magnet brushless dc motor (PMBDCM) fed by a current source inverter (CSI) with thyristors acts as the kernel of the proposed electric drive system. Therefore, the system takes on advantages of both those two devices. The PMBDCM is simulated by FEM. The performance of power electronic converters (PEC) is analyzed analytically and simulated with MATLAB/Simulink. The simulation results show that the main circuit parameters have high influence on the system performance, so the parameters should be optimized by simulation, even by experiment. A prototype is build for verification. The experimental results are in good agreement with the simulation, which validates the feasibility of the proposed electric drive system as well as its design method.

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