Taylor Impact Test를 이용한 금속 재료의 충돌 및 폭발 하중 해석용 고속 물성 유추

이주호 대한기계학회 2022 大韓機械學會論文集A Vol.46 No.10

The design of high-speed machines and defense systems often requires an understanding of the structure's response to extreme environments such as impact and blast load. A model and material property values at high strain rates are needed to analyze the loads accurately. The Taylor impact test is relatively simple and can be performed at high strain rates. A methodology for obtaining the property values of the Johnson-Cook Model that most accurately predicts the Taylor impact test results using the optimization technique is presented. A numerical analysis of the Taylor impact test was performed using the commercial hydrocode AUTODYN. By applying a genetic algorithm-based optimization technique, the property values that facilitated accurate analyses of the Taylor impact test were obtained with minimal numerical analysis. Using this technique, it is possible to obtain a property value that can be used for related analyses. 고속화된 기계 및 다양한 국방 시스템의 설계를 위해 충돌 및 폭발과 같이 극한 환경에 대한 구 조물의 응답에 대한 이해가 필요한 경우가 많다. 이를 정확하게 예측하고 해석하기 위해서는 높은 변형 률 속도에서의 재료의 거동을 잘 모델링할 수 있는 모델과 물성값이 필수적이다. 물성값을 얻기 위한 실험들은 많은 시간과 비용이 소모되기에 상대적으로 간단하고 높은 변형률 속도까지 실험이 가능한 Taylor impact test를 활용하고자 한다. 최적화 기법을 활용하여 Taylor impact test 실험 결과를 가장 정확 히 예측하는 Johnson-Cook model 물성값을 얻는 방법론을 제시하였다. 상용 hydrocodes인 AUTODYN을 활용하여 Taylor impact test 수치해석을 수행하였으며, 유전 알고리즘 기반 최적화 기법을 적용하여 최 소한의 수치해석으로 Taylor impact test를 더 정확히 해석하는 물성값을 획득하였다. 본 기법을 이용하 면 적절한 고속 물성이 없는 경우보다 정확한 물성값을 유추할 수 있으며, 이를 관련 해석에 활용할 수 있을 것으로 기대된다.

Estimation of the saw-tooth shock wave using a lead shock programmer

양태호,Young-Shin Lee,Kon-Whi Yeon,Hyun-Myung Kim,JunYeopKim,Hyuk-Beom Kwon 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.5

Structure durability under shock load is evaluated by performing a shock resistance test. Saw-tooth shock wave is generated in a specific environment and transmitted to the structure. The saw-tooth shock wave is generated using a specific impact test system. In general, the impact test system is generally composed of three types: Drop, lateral and rotational. Each type of impact test system has different detail parts. This study applies the drop-type impact test system. A test table, a fixed table, and a shock programmer compose comprise the drop-type impact test system. The drop-type impact test system uses the initial height of the test table, where the specimen is mounted on. The Impact velocity in the drop-type impact test is determined by the initial height of the test table. The shock programmer generates the shock wave transmitted to the specimen mounted on the test table, which is then. The shock wave transmitted to the specimen is then generated by the shock programmer material. Parameter researchThe parameter testing on the shock programmer has to be performed using the drop-type impact test system to generate the saw-tooth shock wave with non-linear characteristics. This study generates the saw-tooth shock wave by designing and simulating the lead shock programmer. Lead is considered as the shock programmer material. The accuracy of the simulation program (i.e., LS-Dyna) is verified by performing the drop shock test of theon the three types of lead shock programmer with three types. The results of the time history on the test table acceleration between the simulation and the test are compared with those of the shock test and the simulation. The shock test and simulation results are plotted using the tolerance range of the saw-tooth shock wave presented in MIL-STD-810G. The saw-tooth shock wave generated using the lead shock programmer with conical and truncated conical shape is estimated using the verified simulation program. The aspect ratio of the conical and truncated conical lead shock programmer is presented toused to generate the saw-tooth shock wave is also presented.

Repeated lateral impacts on steel grillage structures at room and sub-zero temperatures

Truong, Dac Dung,Shin, Hyun Kyoung,Cho, Sang-Rai Elsevier 2018 International journal of impact engineering Vol.113 No.-

<P><B>Abstract</B></P> <P>This paper presents experimental and numerical investigation results for the plastic response of steel grillages, represented by one longitudinal stiffener and two transverse stiffeners of stiffened plates, used on ships or offshore structures under repeated mass impacts. The repeated mass impact scenario adopted in this paper could represent the repetition of impacted loads on marine structures due to contact with ice floes and floating objects during service. Repeated impact tests on grillage models at room and sub-zero temperatures (−50 °C) were conducted by releasing a knife-edge striker using a drop testing machine. The ends of the grillage models were firmly fixed onto a strong bed with support fixtures. To evaluate the repeated impact performance of the tested models, permanent deflections were measured after each impact test. Additionally, numerical simulations were performed using the commercial software package ABAQUS/Explicit to predict the extent of damage to the tested models caused by repeated impacts. In the calculations, the material properties of tested models were used to determine the strain hardening and strain rate hardening model using the equations recently proposed by the authors. Also, a simple analytical approach has been proposed to predict the damage evolution of the grillage subjected to repeated mass impacts. Reasonable agreement was achieved between the predictions and test results. The results showed that when the structure was repeatedly impacted, permanent deflections of the grillage significantly increased with increasing impact force. The permanent deflections tended to have certain values when the number of impacts increased. Based on the numerical results (which were substantiated with the experimental results), further calculations were then carried out to examine impact responses in greater detail and assess the effects of variations in boundary conditions and strain rate definitions on the response of grillages to repeated mass impacts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Repeated mass impact tests were performed on four steel grillage structures at room and sub-zero temperatures for different kinetic energies. </LI> <LI> Deflection increments were reduced and contact force increased, but impact duration decreased with an increasing number of impacts. </LI> <LI> An analytical method has been developed in this study to predict the permanent deflections of grillage beam under repeated mass impact. </LI> <LI> There is reasonable agreement between the experimental results and predictions of the numerical and analytical analyses developed in this study. </LI> <LI> The effects of strain rate and boundary conditions on the impact responses of grillages were also numerically investigated. </LI> </UL> </P>

Characterization of flow stress at ultra-high strain rates by proper extrapolation with Taylor impact tests

Piao, M.,Huh, H.,Lee, I.,Ahn, K.,Kim, H.,Park, L. Elsevier 2016 International journal of impact engineering Vol.91 No.-

<P><B>Abstract</B></P> <P>This paper is to provide a novel systematic procedure to obtain the dynamic flow stress of a material at ultra-high strain rates ranging from 10<SUP>4</SUP> s<SUP>−1</SUP> to 10<SUP>6</SUP> s<SUP>−1</SUP> where hardening behaviors are difficult to acquire from conventional experiments. Uniaxial material tests with AISI 4340 steel are performed at a wide range of strain rates from 10<SUP>−3</SUP> s<SUP>−1</SUP> to 10<SUP>3</SUP> s<SUP>−1</SUP> by using the INSTRON 5583, a high-speed material testing machine (HSMTM), and a tension split Hopkinson pressure bar (SHPB) testing machine. From the uniaxial tests above, stress–strain curves are obtained at the strain rates ranging from 10<SUP>−3</SUP> s<SUP>−1</SUP> to 10<SUP>3</SUP> s<SUP>−1</SUP>. However, stress–strain curves cannot be obtained at the strain rates higher than 10<SUP>4</SUP> s<SUP>−1</SUP> due to the lack in experimental techniques. In order to characterize hardening behaviors at strain rates ranging from 10<SUP>4</SUP> s<SUP>−1</SUP> to 10<SUP>6</SUP> s<SUP>−1</SUP>, Taylor impact tests are performed when the speed of a projectile is 200 m/s, 253 m/s, and 305 m/s, which entail ultra-high strain rates, high temperature, and large plastic deformation. Flow stresses at the ultra-high strain rates are characterized through an inverse optimization process by comparing the numerical simulation results with the experimental results of the sequentially deformed shapes of a projectile during the Taylor impact test. The thermal softening effect at different strain rates is also considered due to the elevated temperature caused by large plastic deformation. The flow stresses calibrated by the comparison are implemented to numerical simulation resulting in a good coincidence with the Taylor impact tests at different impact velocities. It is noted from the comparison that the yield stress and the comprehensive hardening curves proposed well describe the deformation behavior up to the strain rate of 10<SUP>6</SUP> s<SUP>−1</SUP> beyond the strain rate range for conventional material testing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A systematic procedure has been suggested to obtain the dynamic flow stress of a material at ultra-high strain rates. </LI> <LI> A hybrid experimental–numerical approach has been investigated by using the Taylor impact test. </LI> <LI> The uniaxial tensile tests have been performed at strain rates ranging from 10<SUP>−3</SUP> s<SUP>−1</SUP> to 10<SUP>3</SUP> s<SUP>−1</SUP>. </LI> <LI> The thermal softening effect at different strain rates is considered in the numerical simulations. </LI> <LI> The proposed hardening curves proposed well describe the deformation behavior up to the strain rate of 10<SUP>6</SUP> s<SUP>−1</SUP>. </LI> </UL> </P>

Experimental and numerical investigation of RC column strengthening with CFRP strips subjected to low-velocity impact load

Omer Mercimek,Ozgur Anil,Rahim Ghoroubi,Shaimaa Sakin,Tolga Yilmaz 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.79 No.6

Reinforced concrete (RC) square columns are vulnerable to sudden dynamic impact loadings such as the vehicle crash to the bridges of highway or seaway, rock fall, the collision of masses with the effect of flood and landslide. In this experimental study RC square columns strengthened with and without CFRP strip subjected to sudden low velocity lateral impact loading were investigated. Drop-hammer testing machine was used to apply the impact loading to RC square columns. The test specimens were manufactured with square cross sections with 1/3 geometric scale. In scope of the study, 6 test specimens were manufactured and tested. The main variables considered in the study were the application point of impact loading, and CFRP strip spacing. A 9.0 kg mass was allowed to fall freely from a height of 1.0 m to apply the impact loading on the columns. During the impact tests, accelerations, impact force, column mid-point displacements and CFRP strip strains measurements were taken. The general behavior of test specimens, collapse mechanisms, acceleration, displacement, impact load and strain time relationships were interpreted, and the load displacement relationships were obtained. The data from the experimental study was used to investigate the effect of variables on the impact performances of RC columns. It has been observed that the strengthening method applied to reinforced concrete columns, which are designed with insufficient shear strength, insufficient shear reinforcement and produced with low strength concrete, using CFRP strips significantly improves the behavior of the columns under the effect of sudden dynamic impact loading and increases their performance. As a result of the increase in the hardness and rigidity of the specimens strengthened by wrapping with CFRP strips, the accelerations due to the impact loading increased, the displacements decreased and the number of shear cracks formed decreased and the damage was limited. Moreover, the finite element analyses of tested specimens were performed using ABAQUS software to further investigate the impact behavior.

정적압입 관통 실험을 이용한 복합재 적층판의 고속충격 탄도한계속도 예측

유원영 ( Won Young You ),김인걸 ( In Gul Kim ),이석제 ( Seok Je Lee ),김종헌 ( Jong Heon Kim ) 한국복합재료학회 2013 Composites research Vol.26 No.1

본 논문에서는 유효 면적의 제한이 있는 복합재 적층판의 탄도한계속도를 예측하였다. 탄도한계속도를 예측하기 위해 정적압입 관통실험과 고속충격 실험 그리고 준실험식을 이용하였다. 정적압입 관통실험을 통해 하중-변위 데이터를 취득하고 이를 이용해서 관통에너지를 측정하였다. 고속충격 실험을 통해 실제 관통 속도 및 관통 에너지를 측정하였다. 정적압입 관통실험과 고속충격 실험을 통해 구한 에너지를 이용해 준실험식을 만들고, 준실험식과 고속충돌 실험결과와 비교해 보았다. 위 방법을 이용해 탄도한계속도를 예측하였고 정적압입 관통 실험과 준실험식에 의한 탄도한계속도 예측의 타당성을 확인하였다. The ballistic limit of Carbon/Epoxy composite laminates with the finite effective area are predicted by using the quasi-static perforation test and semi-empirical formula. The perforation energy were calculated from force-displacement curve in quasi-static perforation test. Also, the actual ballistic limit and penetration energy were obtained through the high-velocity impact test. The quasi-static perforation test and high-velocity impact test were conducted for the specimens with 3 different effective areas. In the high-velocity impact test, the air gun impact tester were used, and the ballistic and residual velocity was measured. The required inputs for the semi-empirical formula were determined by the quasi-static perforation tests and high-velocity impact tests. The comparison between semi-empirical formula and high-velocity impact test results were conducted and examined. The ballistic limits predicted by semi-empirical formula were agreed well with high-velocity impact test results.

Experimental Study on the Structural Safety of the Tractor Front-End Loader Against Impact Load

Park, Young-Jun,Shim, Sung-Bo,Nam, Ju-Seok Korean Society for Agricultural Machinery 2016 바이오시스템공학 Vol.41 No.3

Purpose: This study was conducted to experimentally investigate the structural safety of and identify critical locations in a front-end loader under impact loads. Methods: Impact and static tests were conducted on a commonly used front-end loader mounted on a tractor. In the impact test, the bucket of the front-end loader with maximum live load was raised to its maximum lift height and was allowed to free fall to a height of 500 mm above the ground where it was stopped abruptly. For the static test, the bucket with maximum live load was raised and held at the maximum lift height, median height, and a height of 500 mm from the ground. Strain gages were attached at twenty-three main locations on the front-end loader, and the maximum stresses and strains were measured during respective impact and static tests. Results: Stresses and strains at the same location on the loader were higher in the impact test than in the static test, for most of measurement locations. This indicated that the front-end loader was put under a severe environment during impact loading. The safety factors for stresses were higher than 1.0 at all locations during impact and static tests. Conclusions: Since the lowest safety factor was higher than 1.0, the front-end loader was considered as structurally safe under impact loads. However, caution must be exercised at the locations having relatively low safety factors because failure may occur at these locations under high impact loads. These important design locations were identified to be the bucket link elements and the connection elements between the tractor frame and front-end loader. A robust design is required for these elements because of their high failure probability caused by excessive impact stress.

Experimental Study on the Structural Safety of the Tractor Front-End Loader Against Impact Load

( Young-jun Park ),( Sung-bo Shim ),( Ju-seok Nam ) 한국농업기계학회 2016 바이오시스템공학 Vol.41 No.4

This study was conducted to experimentally investigate the structural safety of and identify critical locations in a front-end loader under impact loads. Methods: Impact and static tests were conducted on a commonly used front-end loader mounted on a tractor. In the impact test, the bucket of the front-end loader with maximum live load was raised to its maximum lift height and was allowed to free fall to a height of 500 mm above the ground where it was stopped abruptly. For the static test, the bucket with maximum live load was raised and held at the maximum lift height, median height, and a height of 500 mm from the ground. Strain gages were attached at twenty-three main locations on the front-end loader, and the maximum stresses and strains were measured during respective impact and static tests. Results: Stresses and strains at the same location on the loader were higher in the impact test than in the static test, for most of measurement locations. This indicated that the front-end loader was put under a severe environment during impact loading. The safety factors for stresses were higher than 1.0 at all locations during impact and static tests. Conclusions: Since the lowest safety factor was higher than 1.0, the front-end loader was considered as structurally safe under impact loads. However, caution must be exercised at the locations having relatively low safety factors because failure may occur at these locations under high impact loads. These important design locations were identified to be the bucket link elements and the connection elements between the tractor frame and front-end loader. A robust design is required for these elements because of their high failure probability caused by excessive impact stress.

Experimental Study on the Structural Safety of the Tractor Front-End Loader Against Impact Load

박영준,심성보,남주석 한국농업기계학회 2016 바이오시스템공학 Vol.41 No.3

Purpose: This study was conducted to experimentally investigate the structural safety of and identify critical locations in a front-end loader under impact loads. Methods: Impact and static tests were conducted on a commonly used front-end loader mounted on a tractor. In the impact test, the bucket of the front-end loader with maximum live load was raised to its maximum lift height and was allowed to free fall to a height of 500 mm above the ground where it was stopped abruptly. For the static test, the bucket with maximum live load was raised and held at the maximum lift height, median height, and a height of 500 mm from the ground. Strain gages were attached at twenty-three main locations on the front-end loader, and the maximum stresses and strains were measured during respective impact and static tests. Results: Stresses and strains at the same location on the loader were higher in the impact test than in the static test, for most of measurement locations. This indicated that the front-end loader was put under a severe environment during impact loading. The safety factors for stresses were higher than 1.0 at all locations during impact and static tests. Conclusions: Since the lowest safety factor was higher than 1.0, the front-end loader was considered as structurally safe under impact loads. However, caution must be exercised at the locations having relatively low safety factors because failure may occur at these locations under high impact loads. These important design locations were identified to be the bucket link elements and the connection elements between the tractor frame and front-end loader. A robust design is required for these elements because of their high failure probability caused by excessive impact stress.

Experimental Study on Existing RC Circular Members Under Unequal Lateral Impact Train Collision

Khalil AL-Bukhaiti,Liu Yanhui,Zhao Shichun,Hussein Abas,Xu Nan,Yang Lang,Yan Xing Yu,Han Daguang 한국콘크리트학회 2022 International Journal of Concrete Structures and M Vol.16 No.5

With the fast growth of high-speed rail in recent years, derailment has become the first hidden danger of high-speed rail transportation. The high-speed train passes near the station building. So the train may derail and hit the station building. Building a high-speed railway station usually uses a reinforced concrete structure. As a result of high impact energy on the impact body, the reinforced concrete (RC) member may fail; the impact point is near the member's foot; the structural member's constraint can be considered fixed support. This paper investigates the dynamic behavior of four types of circular reinforced concrete members under unequal lateral impact loads. The RC member's failure mechanism and dynamic response addressed the significance of unequal lateral impact load. The usual circular reinforced concrete members are used as the model to perform the drop-weight impact test. The specimens' crack pattern, failure mechanism, impact, deflection, and strain time–history curves are obtained. Findings show that between the impact point and the adjacent support, shear fractures occur that fail in shear mode. Shear cracks are based on impact velocity, longitudinal reinforcement ratio, and stirrup ratio. One type is more destructive to members and nodes. A shear fracture occurs when a longitudinal reinforcement fractures towards the closer support. The effects of impact velocity, longitudinal reinforcement ratio, and stirrup ratio on the dynamic impact response are studied. The experimental results may help improve structural member impact resistance. The critical section (right side) computed the static shear resistance using shear force, whereas the maximum external load resistance determines static bending moment resistance. Understanding how circular members fail to be subjected to unequal lateral impact loads provides insight into circular RC members' impact design and damage evaluation.