The light-weight and safe design of auto-body structures becomes an important challenging issue in the automotive industry in order to increase the fuel efficiency satisfying the emission-gas regulation of vehicles. The demand for high strength steels with excellent ductility is continually increasing in the automotive industry. So, TRIP steel which have both high strength and ductility have received increased attention.
Recently, passenger safety has emerged as a major concern because of the light weight and faster speed of the vehicle. Collision characteristics must be accurately evaluated to ensure the safety of passengers in the vehicle. If a car runs at sixty kilometers per hour, arithmetical strain rate is a 67 per sec when considering a part of car with 250 millimeters. If a car runs at a hundred kilometers per hour, strain rate is 111 per sec. Therefore, tensile test carried out at 102 ~ 3 × 102 per sec strain rate is needed for crash analysis. But, in the past, the experimental results at quasi-static strain rate were applied to constitutive equation for evaluating crash properties. Recently, a test at the high strain rate can be carried out and test results can apply to constitutive equation. Therefore, it is possible to evaluate the collision characteristics accurately.
In this paper, the tensile testing of TRIP steel sheet for auto-body have been carried out to obtain flow stress-strain curves at the strain rate of 10-2/s to 4 × 102/s. Material constitutive equation is needed to represent the stress at the wide strain rate. The most typical material constitutive equation is Cowper-Symonds equation. And it's used for crash analysis using a computer. The software LS-DYNA for non-linear plasticity analysis was used for crash analysis. The simulation results, which had considered a strain rate influence, and the actual crash test results were compared, and the effectiveness of simulation considered a high speed deformation were evaluated.ABSTRACT =Ⅰ
List of tables =Ⅱ
List of figures =Ⅲ
1. 서론 = 1
2. 이론적 배경 = 3
2.1 변태유기소성형 강판 = 3
2.2 변형률속도 제어 인장시험 = 4
2.2.1 TRIP강의 고속인장시험 필요성 = 4
2.2.2 변형률속도에 따른 인장시험 방법 = 4
2.2.3 변형률속도에 따른 물성 구성방정식 = 6
3. 실험방법 = 10
3.1 시험편 제조 = 10
3.2 고속인장시험 = 12
3.3 실험 결과 처리 방법 = 15
3.3.1 고속인장실험 결과 처리 = 15
3.3.2 Cowper-Symonds equation = 18
3.4 Crash test = 18
3.5 Computer simulation = 22
4. 실험 결과 및 고찰 = 24
4.1 기계적 성질 = 24
4.1.1 True stress-True strain curve = 24
4.1.2 기계적 물성값 결정 = 27
4.1.3 Strain rate sensitivity = 31
4.1.4 Absorbed energy = 33
4.2 Cowper-Symonds equation = 34
4.3 Crash test = 35
4.3.1 Experimental crash test = 35
4.3.2 Computer simulation of crash test = 35
4.3.3 실제 충돌실험과 computer simulation 결과 비교 = 41 4.4 향후 과제 = 41
5. 결론 = 43
6. 참고문헌 = 4
