고강도 냉간압조용 중탄소 Cr-Mo 합금강의 고온변형특성 및 동적재결정 거동 평가

조용덕,이희주,남성실,강현우,장병록 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.6

The hot deformation behavior of medium-carbon Cr-Mo alloy, which has been developed for high strength cold-heading quality wire rod, was investigated to evaluate its hot workability. A flow curve was derived using the hot torsion test, under conditions with temperatures of 1173-1273 K and strain rates of 0.1- 1.0 s-1. At lower deformation temperature and higher strain rate, the overall stress of the flow curve increased, and the flow curve showed a three-stage variation related to the offset of dynamic recrystallization and dynamic recovery. First, as the strain increased, the stress also increased due to work hardening, and reached peak stress. After that, the stress decreased due to softening of the dynamic recrystallization. And when the effect of the dynamic recrystallization and the dynamic recovery reached equilibrium, the stress became steady state. In this paper, the constitutive equation of the peak stress was established using a form of a hyperbolic sine function, and here the thermal activation energy for deformation of the specimen was 244.90 kJ/mol. The peak stresses calculated from the constitutive equation were in good agreement with the experimental results. The dynamic-recrystallized grains were observed using electron backscatter diffraction (EBSD). It showed that the volume fraction of dynamic recrystallization increased as the strain increased under hot deformation. Based on the Avrami kinetic equation, a dynamic recrystallization kinetic model was established. The volume fraction of dynamic recrystallization was predicted from the kinetic model, and can be applied at arbitrary deformation temperatures and strain rates.

A Study on Torsional Characteristics of the Car Body Types at Cornering Motion

Joon-Seong Lee(이준성),Seong-Gyu Cho(조성규) 한국산학기술학회 2017 한국산학기술학회논문지 Vol.18 No.10

탄성변형과 피로손상은 카트의 주행성능에 영향을 미치는 것으로 카트 프레임에 영구변형을 유발할 수 있다. 카트프레임은 현가장치와 다른 장치를 포함하지 않으므로 두 가지 변형에 결정적인 영향을 미칠 수 있는 코너주행 시 동적 거동은 비틀림 변형이 원인이 된다. 선회주행 시 카트의 동적 거동을 분석하기 위해 카트의 GPS추적이 실시간으로 이루어지고 카트프레임에 작용하는 비틀림 응력값을 측정하였다. 레저카트와 레이싱카트의 재료물성치들은 인장실험을 통해 얻었다. 비틀림 응력집중과 프레임 변형은 얻어진 결과 값을 토대로 프레임의 응력해석을 통하여 파악하였다. 개발된 주행분석장치를 이용하여 레저카트와 레이싱카트를 각 조건별로 실차실험을 수행하였고 이를 통한 코너에서 카트의 주행거동을 살펴보았다. 카트가 곡선주행 시 원심력으로 인해 하중이동이 발생하였으며 카트프레임에 비틀림 응력이 발생하였다. 예를 들어 레저카드의 경우, 40 km/h의 속도로 운전할 때 최대 비틀림 피로한도를 측정한 최대 비틀림응력은 230 MPa이며 비틀림 피로한도계수는 0.65를 나타내었다. 뿐만 아니라 카트의 선회 시 운전요소들을 운전측정시스템을 인스톨한 실측장비에서 측정하였으며 카트의 운전거동은 수직변위에 의해 측정하였다. Elastic deformation and fatigue damage can cause the permanent deformation of a kart"s frame during turning, affecting the kart"s driving performance. A kart"s frame does not contain any suspension ordifferential devices and, therefore, the dynamic behavior caused by torsional deformation when driving along a curve can strongly affect these two kinds of deformations. To analyze the dynamic behavior of a kart along a curved section, the GPS trajectory of the kart is obtained and the torsional stress acting on the kart-frame is measured in real time. The mechanical properties of leisure and racing karts are investigated by analyzing their material properties and conducting a tensile test. The torsional stress concentration and frame distortion are investigated through a stress analysis of the frame on the basis of the obtained results. Leisure and racing karts are tested in each driving condition using driving analysis equipment. The behavior of a kart when being driven along a curved section is investigated through this test. Because load movement occurs owing to centrifugal force when driving along a curve, torsional stress acts on the kart"s steel frame. In the case of a leisure kart, the maximum torsional stress derived from the torsional fatigue limit wasfound to be 230 MPa, and the torsional fatigue limit coefficient was 0.65 when driving at a speed of 40 km/h. Furthermore, the driving elements during thecornering of a kart were measured based on an actual auto-test after installing a driving measurement system, and the driving behavior of the kart was analyzed by measuring its vertical displacement.

토션빔액슬 성능 평가를 위한 해석 모델 검증에 관한 연구

최성진(Sungjin Choi),한상원(Sangwon Han),박정원(Jungwon Park),전광기(Kwangki Jeon),최규재(Gyoojae Choi),고형규(Hyunggyu Ko),이동재(Dongjae Lee) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

The torsion beam axle type is widely used in the rear suspension for small passenger cars due to low cost. good performance. etc. To develop the torsion beam axle. it is necessary to estimate of the characteristics of rear suspension from the design process. The characteristics estimation of the torsion beam axle is performed using FEM. dynamic simulation and is veri fied the real test. In this study. the natural frequency and roll stiffness of the torsion beam axil: were measured by FEM. and the reliability of the FE model was evaluated according to the comparison of test data. This study presents a unique method for the finite element modeling and analysis of the torsion beam axle. The results of the FEA were verified using test data.

고속철도용 Antiroll-bar ass'y 국산화 개발

도미나가 야스토시(Yasutoshi Tominaga),편영식(Young-Sik Pyun) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

Antiroll-bar assembly is a precision component designed to control rolling of railway cars. It is important for safe and comfortable ride. Torsion bar is main part of antiroll-bar assembly. Now this part is classified as consumable and imported in Korea from France. Therefore it is necessary, in accordance with Korean environment, to develop domestic torsion bar to reduce cost and improve quality. In this study, development of antiroll bar is analyzed and tested by using road histogram measured on Korean railroads. The comparison with imported bar is drown showing satisfactory results. New design features a ring cover made of SUS steels for corrosion prevention of torsion bar. The safety is examined by CAE analysis and wear tests. As a result, design change did not inflict significant difference in static and fatigue safety. Two different SUS steels were analyzed to determine the best suitable for wear resistance.

고속철도용 안티롤바 어셈블리의 토션바 개발

도미나가 야스토시(Yasutoshi Tominaga),편영식(Young-Sik Pyun),김동일(Dong-Il Kim),최도현(Do-Hyun Choe) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.9

Antiroll-bar Assembly는 철도 차량의 롤링을 제어하도록 설계된 정밀 부품이고 안전과 편안한 승차감을 위해 중요하다. Antiroll-bar Assembly의 주부품인 토션바는 소모품으로써 프랑스에서 전량 수입되고 있다. 따라서 비용절감과 성능향상을 위해 국내 환경에 적합한 토션바 국산화 개발이 필요하다. 본 연구에서는 국내 철도에서 측정된 로드 히스토그램을 활용하여 개발된 토션바에 대한 해석 및 시험을 진행하였고, 수입품과의 비교 시험 결과 만족할만한 결과를 얻었다. 또한 토션바의 부식현상을 방지하기 위해서 스테인리스강 소재의 Ring cover를 씌울 수 있도록 설계를 변경하였다. 변경된 설계 안전성은 CAE해석과 마모시험을 통해서 검증하였다. 이 결과 설계변경에 의한 정적 및 피로에 대한 안전성은 큰 차이가 없었다. 그리고 2종류의 스테인리스강 중에서 내마모성이 우수한 소재를 채택하였다. An antiroll-bar assembly is a precision component that is designed to control the rolling of railway cars. It is important for ensuring a safe and comfortable ride. A torsion bar is the main part of the antiroll-bar assembly. Now, this part is classified as a consumable, and it is imported into Korea from France. Therefore, there is a strong need to domestically develop a torsion bar suitable for Korean conditions and to reduce cost and improve quality. In this study, an antiroll bar is developed, and it is analyzed and tested by using a road histogram measured on Korean railroads. This bar shows satisfactory results in a comparison with the imported bar. It has a novel design featuring a ring cover made of SUS steels to prevent the corrosion of the torsion bar. Its safety is examined through CAE analysis and wear tests. It is found that its design does not result in a significant difference in static and fatigue safety. Two different SUS steels were investigated in terms of their wear resistance, and the best one was adopted.

ECAP으로 제조된 초미세립 저탄소강의 동적 변형거동

이한상,황병철,이성학,안병두,신동혁,이창길 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.4

Dynamic deformation and fracture behavior of ultra-fine-grained low-carbon steels fabricated by equal channel angular pressing (ECAP) was investigated in this study. Dynamic torsional tests were conducted on four steel specimens, two of which were annealed after ECAP, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and fracture mode. The ECAP'ed specimen consisted of very he, elongated grains of -0.5 μm in size, which were slightly coarsened and had an equiaxed shape after annealing. The dynamic torsional test results indicated that maximum shear stress decreased, while fracture shear strain increased, with increasing annealing time. Some adiabatic shear bands were observed at the gage center of the dynamically deformed torsional specimen, and their width was smaller in the ECAP'ed specimen than in the 1-hr annealed specimen, although they were not found in the 24-hr annealed specimen. Ultra-he, equiaxed grains of 0.05-0.3 μm in size were formed inside the adiabatic shear band, and their boundaries had characteristics of high-angle grain boundaries. These phenomena were explained by dynamic recovery and recrystallization due to the highly localized plastic deformation and temperature rise inside the adiabatic shear band. (Received February 11, 2004)

ECAP으로 제조된 초미세립 5083 Al 합금의 동적 변형거동

김양곤,황병철,이성학,김우겸,신동혁 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.1

Dynamic deformation behavior of ultra-fine-grained aluminum alloys fabricated by equal channel angular pressing (ECAP) was investigated in this study. Dynamic torsional tests were conducted on four aluminum alloy using a torsional Kolsky bar, and then the test data were analyzed in relation to microstructures, tensile properties, and adiabatic shear band formation. The ECAP'ed specimens consisted of a considerable amount of second phase particles, which were refined and had an equiaxed shape as the ECAP pass number increased. The dynamic torsional test results indicated that maximum shear stress increased, while fracture shear strain remained constant, with increasing ECAP pass number. Observation of the deformed area beneath the fracture surface after the dynamic torsional test indicated that a number of voids initiated mainly at second phase particle/matrix interfaces, and that the number of voids increased with increasing pass number. Adiabatic shear bands of 100-150μm in width were formed in the as-extruded and 1-pass specimens having coarser second phase particles, while they were hardly formed in the 4-pass and 8-pass specimens having finer second phase particles. The possibility of the adiabatic shear band formation was explained by concepts of absorbed deformation energy and void initiation. (Received October 29, 2004)

ECAP으로 제조된 초미세립 저탄소강의 단열성 전단밴드의 미세조직 변화

황병철,이성학,김용찬,김낙준,신동혁 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.5

The object of the present study is to investigate the microstructural development of the adiabatic shear band formed by dynamic torsional experiments of ultra-fine-grained low-carbon steels fabricated by equal channel angular pressing (ECAP). Dynamic torsional tests were conducted on four steel specimens, two of which were annealed after ECAP, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and fracture mode. The ECAP'ed specimen consisted of very fine, equiaxed grains of 0.2 !Am in size, which were slightly coarsened and had an equiaxed shape after annealing. Some adiabatic shear bands were observed at the gage center of the dynamically deformed torsional specimen, and their width was smaller in the ECAP'ed specimen than in the 1-hr annealed specimen, although they were not found in the 24-hr annealed specimen. Ultra-fine, equiaxed grains of 0.05~0.2 μm in size were formed inside the adiabatic shear band, and their boundaries had characteristics of high-angle grain boundaries. These phenomena were explained by dynamic recovery and recrystallization due to the highly localized plastic deformation and temperature rise occurred within the shear band. The temperature rise in the shear band formation process was inferred to be above 540℃ from the observation of spheroidization behavior of cementites in pearlite grains. (Received February 7, 2005)

미세한 α_2-Ti_3Al상이 석출된 Ti-6Al-4V 합금의 동적 변형거동

이동근,이성학,이종수 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.1

In this study, Widmansta¨tten and equiaxed microstructures containing very fine α_2 particles were obtained by overaging a Ti-6Al-4V alloy, and their dynamic deformation behavior was investigated. Dynamic torsional thests were conducted by using a torsional Kolsky bar, and deformed microstructures and torsionally deformed areas beneath fracture surfaces were observed to investigate various factors affecting dynamic deformation properties of α, β and their interfaces. The dynamic torsional test results indicated that maximum shear stress and fracture shear strain of the over-aged Winmansta¨tten and equiaxed microstructures were higher than those of the unaged microstructures. The possibility of the adiabatic shear band formation under dynamic loading was quantitatively analyzed, based on the observation how plastic deformation energy was distributed to void initiation and adiabatic shear banding. Since the number of voids formed in the over-aged microstructures drastically increased because of the α_2 precipitation, driving force for the adiabatic shear band formation decreased as much as deformation energy used for the void formation, thereby reducing the possibility of the adiabatic shear band formation. These findings provided a new idea how to improve ballistic performance of Ti alloy armor plates because the over-aging of the Ti-6Al-4V alloy was effective on both the improvement of tensile and dynamic torsional properties and the reduction in the possibility of the crack initiation due to adiabatic shear banding.

Ti-6Al-4V 합금의 동적변형특성과 탄도충격성능 : 2. 동적비틀림 특성과 탄도충격성능 2. Dynamic Torsional Properties and Ballistic Performance

이동근,이유환,이성학,이종수,이충열,허선무 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.10

The effects of microstructural morphology on dynamic deformation and fracture behavior and ballistic performance of a Ti-6Al-4V alloy were investigated in this study. Ballistic impact tests were conducted on equiaxed and bimodal microstructures, which were processed by different heat treatments, and then the test data were analyzed in relation to microstructures, tensile properties, and dynamic torsional test data. In the impacted region of the equiaxed microstructure, a number of adiabatic shear bands and cracks were observed to be formed along plastic flow lines, and delamination occurred because of cracking along the plastic flow lines or shear bands. In the case of the bimodal microstructure, shear bands were found in limited area near the impacted region without occurring delamination, and their number was fewer than that of the equiaxed microstructure. Thus, ballistic performance of the bimodal microstructure was better than that of the equiaxed microstructure. The ballistic performance of the two microstructures was also discussed by comparing the possibility of adiabatic shear band formation obtained from dynamic torsional test data.