Validation of dynamic hardening models at high strain rates using Taylor impact tests = 테일러 충격시험을 이용한 고 변형률속도 조건에서의 동적 경화모델 검증

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The dynamic plastic deformation is an important process in many industries, such as automobile crashworthiness, satellite protection, ballistic impact, and armor crashworthiness. Accurate numerical simulations require a reliable constitutive description of the flow stresses at wide range of strain rates. Dynamic hardening models can interpolate flow stresses up to strain rate of 10^3 /s because of limited testing conditions. However, the reliability of material properties at higher strain rates (10^5 /s ~ 10^6 /s) cannot be guaranteed from these models. Effective plastic strain rate of 10^5 /s was observed from Taylor impact test numerical simulation at impact velocity of 200 m/s. Taylor impact test, thus, is one of the most famous test methods to evaluate the performance of dynamic hardening models at relatively high strain rates.Several tensile and compressive experiments were conducted for 4340 steel, OFHC copper, and Ti6Al4V alloy at wide range of strain rates. Flow stresses at low strain rates, from 10^-3 /s to 10^-1 /s, and high strain rates, 10^2 /s, can be obtained from universal testing machine (Instron 5583) and Split Hopkinson Pressure Bar (SHPB) testing machine. High Speed Material Testing Machine (HSMTM) can be utilized to obtain flow stresses at intermediate strain rates, from 10^0 /s to 10^2 /s. In this study, 3 different impact velocities were performed for Taylor impact tests to evaluate the Johnson-Cook model, modified Johnson-Cook model, modified Khan-Huang model, and Lim-Huh model for 4340 steel, OFHC copper, and Ti6Al4V alloy, respectively, at relatively high strain rates. The material coefficients of four different models can be obtained from the experimental flow stress results. An effective alignment control jig system was designed and manufactured for Taylor impact tests. Photron FASTCAM SA4 high speed camera with Nikon AF Micro Nikon 60 mm lens was used for recording for Taylor impact tests. 192 x 64 pixel resolution and 180,000 fps ...
Advisors
Huh, Hoonresearcher허훈
Description
한국과학기술원 : 기계공학전공,
Publisher
한국과학기술원
Issue Date
2013
Identifier
566239/325007  / 020114544
Language
eng
Description

학위논문(석사) - 한국과학기술원 : 기계공학전공, 2013.8, [ ix, 81 p. ]

Keywords

High strain rate; Dynamic hardening model; 테일러 충격시험; 변형률속도; Taylor impact test; 동적 경화모델

URI
http://hdl.handle.net/10203/197513
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=566239&flag=dissertation
Appears in Collection
ME-Theses_Master(석사논문)
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