A 3-D computational method to simulate stable growth of a macroscopic crack under model I condition is described in this paper. The Gurson-Tvergaard plasticity model for voided materi-als describes the damage process. Fixed-sized, computational cell elements (containing voids) defined over a thin layer at the crack plane simulate the ductile crack extension. Outside of this layer, the material remains undamaged by the void growth, follows the conventional J2 flow theory. The micromechanics parameters controlling crack growth are D, the thickness of com-putational cell layer and fo, the initial void porosity. Calibration of these parameters proceeds through analyses of ductile tearing to match R-curve obtained from testing of deep notch bend specimens for welded joints. The effect of the strength mismatching on ductile crack growth for welded joints is simulated also.

The changes in mechanical properties and fracture toughness by dynamic loading were investigated with experiments. The parameter R, which can reflect the effect of the loading rate and the temperature rising during the high loading rate, could be employed to describe the constituent relation for the typical structure steel and its weld metal. The dynamic loading effect on the stress/strain fields and the temperature variation in the vicinity of the crack tip was analyzed by the finite element method, the dynamic fracture behavior was evaluated based on the local approach. It has been found that the Weibull stress is an effective fracture parameter, independent of the temperature and the loading rate.

In this paper, a commercial metal-based ceramic coating has been used to prepare the specimen adopting high velocity electric arc spraying (HVAS) technology. The three-point bend tests were proposed to measure the Young's modulus (E) of the coating. A test specimen capable of measuring the complex stress intensity factor of bi-material interfacial crack has been devised. The finite element method (FEM) was conducted to investigate the stress fields in the vicinity of the crack for the bend specimen, and the complex stress intensity factor and its phase angle have been computed through the stress field. The test results of determining E of the coatings showed the Young's modulus increased with the increase of coating thickness. The reason was that the rise of coating thickness resulted in the reduction of porosity in the coatings, so the Young's modulus followed it. The toughness test results showed that crack initiation of the interfacial crack occurred in the range of linear elastic for the whole specimen. In addition, the analysis on validity of K showed that the stress intensity factor was able to be used as the fracture-controlled parameter of interface crack for the specimen geometry and loading pattern in this paper.

In present, due to continuous increasing of the fracture toughness and continuous reduction of steel plate thickness for ultra-high strength steel used in the aerospace solid rocket motor, it is difficult to measure its fracture toughness of surface crack using the linear elastic fracture mechanics method. In this paper, the tensile test was used to achieve the conditional load when the surface crack initiation occurred. Then, the finite element method (FEM) was conducted to calculate the ductile fracture toughness JIC under the conditional load. Lastly, the surface crack fracture toughness, KIe, can be computed from JIC based on the fracture mechanics method. In addition, the analysis on validity of J-integral showed that KIe converted from JIC was able to evaluate the fracture toughness of ultra-high strength steel. These are important technical parameters for design of aerospace solid rocket motor.

For the purpose of finding a way to control effectively the residual thermal stresses induced by local heat treatment on spherical vessels, a thermal tracing program is developed successfully based on the transient thermal analysis and controlling method of average temperature of nodes located in an "observed region." Typical calculation cases reveal that the local heat treatment process itself does cause obvious residual thermal stress that is high enough to cause yield when concentrated heating on small region is adopted, but decentralized heating on a larger region can lower effectively the residual thermal stresses to a rather desirable level. It can be found through a one by one analysis of ten factors, which are possibly influential on residual thermal stress: arc radius of heated region, holding temperature, volume, and wall thickness of the vessel are primary effective factors. The bandwidth of the annular insulated region, the heating rate, and the size of the observed region are secondary factors. Heating pattern, holding time, and cooling rate can hardly affect the residual thermal stress. Considering the primary factors except holding temperature, and taking 30% of yield stress as the expected residual thermal stress level, the recommended arc radius of heated region should be 2.2 Rt in minimum.