On Shrinkage Cavities Shape Modeling for Fatigue Simulation of A356 Alloy Specimen

A356 합금 시편의 수축공 결함형상에 대한 피로해석용 형상 모델링 방법

Abstract

During the casting process, it is possible to minimize shrinkage and blowholes by modifying the casting design. However, it is impossible to eliminate these factors completely. Therefore, mechanical design engineers apply a sufficient safety factor owing to the possibility of insufficient performances of the cast products. In this paper, prediction method of the fatigue life of cast products containing shrinkage is conducted by using CT (computed tomography) and the SSM (shape simplification method), and additional fatigue analyses are carried out. The analysis results are then compared to results from actual experiments on samples with shrinkage defects. It is found to be that the considering actual shrinkage in cast products by means of stress and fatigue analyses is more accurate and effective. It is also considered that the proposed hot spot method provides us a good tool to predict the fatigue lifes of cast product.

Fig. 1. Schematic diagram of specimen.

Fig. 2. Fracture sections after fatigue test.

Fig. 3. RayScan X-ray inspection system.

Fig. 4. Shrinkage defects of the test specimen by CT scan.

Fig. 5. Shrinkage defect shapes extracted from the specimens.

Fig. 6. Shrinkage cavities modeling of each specimens (SSM by multi ellipsoids).

Fig. 7. Shrinkage cavities modeling of each specimens by simplification of shape method.

Fig. 8. Hot spot stress method in weld notch area(Stress extrapolation).

Fig. 9. Results of Stress and fatigue Analysis in 2-1 specimen.

Fig. 10. Results of the experiment, analysis and hot spot stress method.

Table 1. Chemical composition of the A356 specimen.

Table 2. Conditions of heat-treatment for the specimen.

Table 3. Mechanical Properties of tensile test specimens.

Table 4. Results of the fatigue test.

Table 5. Results of the experiment, analysis and hot spot stress method.