저자명 박충희 
년도 2013 

This study is concerned with the effect of the strain rate on the strain hardening behavior of polymer-bonded explosives (PBXs) at a wide range of strain rates. When PBXs are applied in a warhead system that undergoes severe dynamic loading conditions, it is very important to investigate the deformation behavior of PBXs subjected to dynamic loads in order to guarantee the safety of the warhead system before explosion. PBXs in the warhead system undergo not only localized large deformation with high strain rates induced by direct dynamic loads but also small deformation with low and intermediate strain rates due to stress wave propagation. The strain hardening behavior of PBXs at quasi-static states, intermediate and high strain rates should be thoroughly investigated to perform the design of the warhead system because PBXs undergo deformation at a wide range of strain rates irregularly distributed in PBXs from quasi-static states to high strain rates. It is noticed that the strain hardening behavior of PBXs varies significantly as a function of the strain rate. It is, hence, essential to incorporate the effect of the strain rate on the strain hardening behavior of PBXs in the numerical simulation of the warhead to predict the deformation behavior of PBXs accurately.

In previous research works, it was demonstrated that the flow stresses generally increase as the strain rate increases in various PBXs. The effect of the strain rate can be explained by the intrinsic characteristics of the polymer matrix. It is noticed that the elastic modulus and flow stress of polymers increase significantly as the strain rate increases. The effect of the strain rate on the strain hardening behavior of PBXs is highly influenced by the mechanism of failure in accordance with the strain rate as well as the intrinsic characteristics of the polymer matrix. It was reported that the debonding stresses between the particles and the polymer matrix increase as the elastic modulus of the polymer matrix increases. The debonding stresses between the particles and the polymer matrix increase as the strain rate increases since the elastic modulus of the polymer matrix increases with increasing strain rates. It corresponds to the previous research work reporting that the crystal fracture of particles became the dominant failure mechanism in uniaxial compressive tests at high strain rates while the debonding, which can also be expressed as the interfacial failure, was the dominant failure mechanism in uniaxial compressive tests at low strain rates.

In this study, uniaxial compressive tests of two kinds of PBX simulants classified into particulate composites were conducted at a wide range of strain rates ranging from 10-4 s-1 to 3,870 s-1 to investigate the effect of the strain rate on the strain hardening behavior of PBXs. The dynamic material testing machine (Instron 8801) was utilized for uniaxial compressive tests from quasi-static states to low strain rates ranging from 10-4 s-1 to 100 s-1 and the developed high speed material testing machine (HSMTM) was used for uniaxial compressive tests at intermediate strain rates ranging from 101 s-1 to 102 s-1. A new jig system was designed and utilized for uniaxial compressive tests at intermediate strain rates using the HSMTM so that uniaxial compressive tests can be conducted within the designated strain. The split Hopkinson pressure bar (SHPB) was used for uniaxial compressive tests at high strain rates ranging from 1,250 s-1 to 3,870 s-1. For SHPB tests, preceding researches such as determination of the bar material of the SHPB system, pulse shaping techniques and consideration of the variation of the true strain rate were conducted to acquire accurate stress--strain relationships of soft materials including PBXs at high strain rates. The significant effect of the strain rate on the strain hardening behavior during uniaxial compressive deformation is quantitatively investigated from the experimental data at various strain rates.

A new rate-dependent hardening model based on the DSGZ model was proposed from the investigated result to model the effect of the strain rate on the strain hardening behavior of PBXs. The model gives a concise expression of the stress dependence on the strain and strain rate with a second-order exponentially-increasing strain rate sensitivity function. The model is capable of representing the non-linear viscoelasticity, yielding and subsequent strain softening behavior. It can also describe the steady-state behavior at large strain. The proposed model was implemented in the commercial finite element analysis (FEA) software, LS-DYNA, with the user defined material models (UMAT). Finite element analyses of uniaxial compressive tests at various strain rates were conducted with the implemented UMAT to validate the proposed model. The comparisons of FEA results with the experimental data show that the proposed model was successfully able to describe the significant effect of the strain rate on the strain hardening behavior of PBXs.

 

Keywords: Polymer-Bonded Explosive (PBX), PBX Simulant, Split Hopkinson Pressure Bar Test, Rate-Dependent Hardening Model, Strain Rate Sensitivity

번호 제목 저자명 날짜 조회 수
27 Anisotropic Fracture Limit for the Failure Prediction of Advanced High-Strength Steel Sheets (고강도 강판의 파괴 예측을 위한 이방성 파괴 한계에 관한 연구) 박남수  2017.06.07 64
26 A Study on the Nonlinear Behaviors of Polymer-Bonded Explosives Considering Stress Softening Effect(응력연화현상을 고려한 복합화약의 비선형 거동에 관한 연구) 염기선  2013.09.08 4719
» Rate-Dependent Hardening Model for Polymer-Bonded Explosives Considering a Wide Range of Strain Rates (광범위한 변형률속도를 고려한 복합화약의 변형률속도 의존 경화모델) 박충희  2013.08.30 3533
24 Dynamic Failure Criteria of a Laser-welded Region under Combined Loading Conditions for Auto-body Crash Analyses (차체용 부재의 충돌해석을 위한 복합하중조건에서 레이저 용접부의 동적 파단조건 연구) 하지웅  2013.04.14 7229
23 Rate Dependent Hardening Model for Pure Titanium Considering the Effect of Deformation Twinning (쌍정의 영향을 고려한 티타늄의 변형률속도 의존 경화 모델) 안광현  2012.12.12 16932
22 Strain-Rate Dependent Anisotropic Yield Criteria for Auto-body Steel Sheets (자동차용 강판의 변형률속도 의존 이방성 항복함수에 관한 연구) 허지향  2012.12.11 17785
21 A New Ductile Fracture Criterion for the Formability Prediction of Steel Sheets and Its Application to Finite Element Analysis (강판의 성형성 예측을 위한 새로운 연성 파괴 조건 및 유한 요소 해석에의 응용) [1] Yanshan Lou  2012.12.10 20813
20 Measurement Uncertainty Evaluation for High Strain Rate Tensile Properties of Auto-body Steel Sheet (자동차용 강판 고속인장물성 데이터의 측정불확도 산출) 정세환  2012.12.10 17566
19 A Study on a Continuum Damage Yield Function to Predict Ductile Fracture of Materials (재료의 연성파단을 예측하기 위한 연속체 손상 항복 함수에 관한 연구) 고윤기  2012.12.10 14432
18 A Study on the Tension/Compression Hardening Behavior of Auto-body Steel Sheets Considering the Pre-strain and the Strain Rate (초기 변형률 및 변형률 속도를 고려한 차체 강판의 인장/압축 경화 거동에 관한 연구) [1] 배기현  2011.01.11 20139
17 Forming Limit Diagram of Auto-body Steel Sheets at High Strain Rates for Sheet Metal Forming and Crashworthiness (박판성형 및 충돌성능 향상을 위한 고변형률속도에서의 차체강판 성형한계도) 김석봉  2010.07.13 21409
16 Evaluation of a cast-joining process of dual metal crankshafts for heavy-duty engines with ductile cast iron and high strength forged steel(구상흑연주철과 고강도 단조강의 주조접합 이종금속을 이용한 중대형 엔진 크랭크샤프트의 평가) 한 신  2010.07.13 17684
15 A Study on Material Properties of OFHC Copper Film at High Strain Rates using High-Speed Micro Material Testing Machine (고속마이크로재료시험기를 이용한 무산소동 박판의 고변형률속도 재료물성치 연구) 김진성  2010.07.13 20005
14 Microscopic investigation of the strain rate hardening for auto-body steel sheet(차체강판 변형률속도 경화의 미시적 관찰) 윤종헌  2010.07.13 16726
13 Analysis of Elasto-Plastic Stress Waves by a Time Discontinuous Variational Integrator of Hamiltonian with a Second-Order Integration Scheme of the Constitutive Model (해밀토니안의 시간 불연속 변분적분기와 구성방정식의 2차 정확도 적분법을 이용한 탄소 조상순  2008.12.15 21484
12 A Study on the Dynamic Failure Model of a Spot Weld under Combined Loading Conditions for Auto-body Crash Analyses (차체용 부재의 충돌해석을 위한 복합하중조건에서 점용접부의 동적 파단모델 연구) [1] 송정한  2008.07.24 18359
11 Study on Dynamic Tensile Tests of Auto-body Steel Sheet at the Intermediate Strain Rate for Material Constitutive Equations (차체강판의 중변형률 속도에서의 동적 인장시험 및 물성 구성방정식에 관한 연구) 임지호  2005.11.29 25274
10 Dynamic Formulation of Finite Element Limit Analysis for Impact Simulation of Structural Members (구조부재의 충돌해석을 위한 유한요소 극한해석의 동적 수식화) 김기풍  2005.11.29 17588
9 Finite Element Inverse Approach and Initial Guess Generation for Sheet Metal Forming Analysis of Complicated Auto-body Members (복잡한 차체부재의 박판성형공정을 위한 유한요소 역해석 및 초기추측치 계산) 김승호  2005.11.29 18904
8 Development of a Nonlinear Degenerated Shell Element with the Drilling Degree of Freedom by the Cubic Polynomial Interpolation and the Assumed Strain Method (드릴링 자유도의 삼차 근사법과 대체변형률법을 이용한 비선형 감절점 쉘 요소의 개발) 이형욱  2005.11.29 17495