분자동역학 해석 기반 가교율에 따른 에폭시 폴리머의 항복 표면 형상 평가
Evaluation of yield surfaces of epoxy polymers considering the influence of crosslinking ratio: a molecular dynamics study
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본 연구에서는 복합소재의 기지재로 활용되고 있는 에폭시 고분자의 가교율이 항복표면에 미치는 영향을 분자동역학 해석을 통해 평가하고자 한다. 분자동역학 해석을 활용하여 가교율에 따른 에폭시 모델을 형성한 후, 상온-대기압 조건하에서 단축 변형 해석 및 평면응력 조건을 고려한 다축 변형 해석을 수행하였으며, 해석 데이터를 통하여 가교율에 따른 영률, 항복점, 항복표면, 그리고 경화지수를 도출하였다. 해석 결과, 영률 및 응력은 기존 선행 연구들에서 조사되었듯이, 가교율에 따라 증가하는 경향을 확인하였다. 다축 변형 시에는, 이러한 가교율과 도출된 응력간의 관계가 하중의 방향에 따라 의존적임을 확인하였는데, 가교율이 증가할수록 단축 인장 영역에 비해, 이축 압축 영역의 항복표면은 빠른 속도 팽창하였으며, 이로 인한 항복표면의 상이함을 관측하였다. 이를 통해, 고분자 소재의 항복 표면의 압력의존성은 소재의 가교 정도에 의존적이며, 항복이 진행될수록, 압력의존성은 동일 소재 하에서도 변할 수 있음을 확인하였다.
Abstract
This study focuses on investigating the influence of epoxy polymer crosslinking density, a crucial aspect in composite material matrices, on the yield surface using molecular dynamics simulations. Our approach involved generating epoxy models with diverse crosslinking densities and subjecting them to both uniaxial and multiaxial deformation simulations, accounting for the elasto-plastic deformation behaviors. Through this, we obtained key mechanical parameters including elastic modulus, yield point, and strain hardening coefficient, all correlated with crosslinking conversion ratios. A particularly noteworthy finding is the rapid expansion of the yield surface in the biaxial compression region with increasing crosslinking ratios, compared to the uniaxial tensile region. This unique behavior led to observable yield surface variations, indicating a significant pressure-dependent relationship of the yield surface considering plastic strain and crosslinking conversion ratio. These results contribute to a deeper understanding of the complex interplay between crosslinking density and plastic mechanical response, especially in the aspect of multiaxial deformation behaviors.
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