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Although ductile fracture properties of aluminum alloy have been examined by several research works, the effect of strain rate in small punch test is still unclear. An investigation on rate sensitivity of fracture mechanical characteristics of aluminum alloy in small punch test is necessary. In the present study, an experimental investigation of small punch test is performed at different deformation rate in quasi-static test for aluminum alloy 1050-H14. The strain-rate sensitivity of fracture properties are discussed based on the force-deflection curve as well as observation of fracture surface of deformed specimen after testing. The obtained results show that the material possesses a positive rate-sensitivity in the investigated range of displacement rate from 0.48 to 1.26 mm/min. The necking appears in a small region due to inhomogeneous deformation in the direction of cross-section at lower deformation rate. In the case of higher rate of deformation, more uniform deformation in the direction of cross-section and the local ductile fracture with more dimples can be observed.

Among stainless steel, type-304 austenitic stainless steel is the most widely used because of high corrosion-resistance as well as favourable mechanical properties due to strain-induced martensitic transformation (SIMT). In order to utilize the application of type-304 austenitic stainless steel in dynamic loading condition, the fracture behaviours with the effect of the local distribution of SIMT in the bending deformation using a relatively small specimen need to be investigated. The effect of SIMT as well as thermal softening phenomenon at a high deformation rate has been examined insufficiently and mechanism for rate-sensitivity of fracture-mechanical characteristic is still unclear. In present study, experiment and FE simulations are performed for the SP test at different deflection rates for type-304 austenitic stainless steel. In order to describe the damage and fracture process of materials, a modified version of the Johnson–Cook damage model is applied. After confirming the validity of computation, the rate-sensitivity of fracture-mechanical characteristics of the steel is examined at room temperature. In addition, the effects of temperature and SIMT on the force-deflection curve and fracture properties are discussed to clarify the mechanism for an improvement of impact fracture-mechanical characteristics of the steel.

Energy absorption of steel with Transformation-induced Plasticity (TRIP) under bending deformation needs to be carefully examined at very high strain rates for its new applications in the automotive industries. Energy absorption members made of the steel can suppress severe damages by traffic accidents. However, it is difficult to apply three-point bending test based on the split Hopkinson pressure bar (SHPB) method because a use of a thick pre-cracked specimen is required for such materials with high toughness. In contrast, if the impact small punch test, which dominant deformation mode of a relatively-small specimen is bending, is established, its experimental arrangement might become simpler and the SHPB technique is applicable. In this study, a novel and reliable impact small punch testing method based on SHPB technique with high accuracy is developed for an investigation on impact energy absorption of the steel with TRIP. Besides, its design, feasibility and validity are confirmed by finite element simulation for austenitic stainless steel SUS304, a representative of steel with TRIP. The obtained experimental as well as computational results show that the developed testing apparatus for impact small punch test based on SHPB technique is reliable and reasonable for the investigation on impact energy absorption of the high toughness material including steel with TRIP.

It is considered that fracture toughness of TRIP steel can be evaluated by means of the small punch (SP) test. However, a mechanism of improving fracture toughness in the SP test for TRIP steel under the impact condition might not be clarified through merely experimental works because the effect of strain-induced martensitic transformation (SIMT) coupled with temperature in TRIP steel becomes quite complicated at high deformation rate. Therefore, a computational simulation on the SP test for an evaluation of the mechanism is indispensable. Since the specimen in the SP test will be fractured at a certain level of deformation, it is necessary to express the fracture by incorporating damage model into constitutive equation of the material in simulation of the SP test. In the present study, a finite element analysis is performed for the SP test with a specimen made of type-304 austenitic stainless steel by an inclusion of damage parameter and its evolution equation. After showing the validity of the computation, the effects of deformation rate, temperature, and SIMT on the force-deflection curve and deformation behavior are examined. Then, the mechanism of rate-sensitive fracture toughness in TRIP steel is challenged to be clarified.

Gen gdhA mã hoá cho NAPH- GDH từ vi khuẩn E.coli khi biểu hiện trong cây thuốc lá đã làm tăng cường khả năng chống chịu thuốc bảo vệ thực vật, tăng sinh khối thực vật và tăng khả năng chịu hạn, ngoài ra khi biểu hiện ở cây ngô đã cho thấy gen gdhA giúp cây ngô tăng năng suất và sự tăng năng suất có được là nhờ cải thiện khả năng chịu đựng hạn của cây. Với mục đích có nguồn gen giá trị này, chúng tôi tiến hành phân lập gen gdhA từ chủng vi khuẩn E. coli JM109, tạo dòng và xác định trình tự gen gdhA để tìm sự khác biệt về gen trong chủng hiện có. Đồng thời, chúng tôi thực hiện cải biến trình tự gen gdhA bằng phần mềm OptimumGeneTM cho phù hợp với thực vật. Gen gdhA sau khi cải biến được ghép nối với promoter CaMV 35S và 35S terminator trong vector trung gian pRTRA 7/3 để tạo cấu trúc biểu hiện 35S::gdhA::35S. Cấu trúc này đã được chuyển vào vector pCAMBIA1300 tạo nên vector biểu hiện thực vật mang gen gdhA và biến nạp vector vào tế bào vi khuẩn A.tumefaciens chủng EHA105. Để kiểm tra sự biểu hiện của gen gdhA chúng tôi tiến hành chuyển cấu trúc biểu hiện gen gdhA vào cây mô hình thuốc lá N. tabacum K326 thông qua A. tumefaciens. Phân tích sự có mặt của gen trong 20 dòng cây thuốc lá chuyển gen bằng PCR và RT-PCR cho thấy 2/20 dòng thuốc lá chuyển gen có mang gen gdhA hoạt động ở mức độ phiên mã tạo mRNA. Sự biểu hiện của cấu trúc này ở cây thuốc lá cho thấy có thể sử dụng cấu trúc mang gen để chuyển gen gdhA vào cây trồng đích như cây ngô.

Transformation-induced plasticity (TRIP) steel might have a high energy-absorption characteristic because it could possibly consume impact energy by not only plastic deformation but also strain-induced martensitic transformation (SIMT) during deformation. Therefore, TRIP steel is considered to be suitable for automotive structures from the viewpoint of safety. Bending deformation due to buckling is one of the major collapse modes of automotive structures. Thus, an investigation on the bending deformation behavior and energy-absorption characteristic in TRIP steel at high deformation rate is indispensable to clarify the mechanism of better performance. Some past studies have focused on the improvement of mechanical properties by means of SIMT; however, the mechanism through which the energy-absorption characteristic in steel can be improved is still unclear. In this study, the three-point bending deformation behavior of a beam specimen made of type-304 austenitic stainless steel, a kind of TRIP steel, is investigated at various deflection rates by experiments and finite-element simulations based on a constitutive model proposed by one of the authors. After confirming the validity of the computation, the rate-sensitivity of energy absorption from the viewpoint of hardening behavior is examined and the improvement of the energy-absorption characteristic in TRIP steel including its mechanism is discussed.

In the last few decades, energy absorption of materials becomes an critical issue in a design process of a vehicle because risks of primary and secondary accidents against pedestrians, other road users and structures can be reduced by a performance of absorbing energy in its support structures. Among various materials used for the structures, TRIP steel with favorable mechanical properties such as excellent formability and higher impact energy absorption is attractive to automotive industries. Huge numbers of research works have been carried out to investigate deformation behavior of TRIP steel. However, just few studies can be found on the performance in TRIP steel, especially, at higher deformation rate during the crash of the vehicle. Kinetic energy by higher speed of the vehicle will be consumed by inelastic bending deformation of components. Thus, a consideration of bending deformation at high impact velocity is required for the evaluation of the performance. In this study, the performance in TRIP steel at high deformation rate is clarified by conducting both quasi-static and impact three-point bending tests for pre-cracked specimen.

Journal of Clinical Virology, 66, pp.24-26; 2015

Among various materials used for structures, TRIP steel has attracted the interest of the scientific community because TRIP steel indicates better performances such as formability, toughness and energy absorption as well as strength and ductility than other kinds of advanced high strength steel because of strain-induced martensitic transformation. From a microstructural point of view, two mechanisms are usually considered to explain the high performances: the Magee and the Greenwood-Johnson effects: however, it has not been proven yet. On the other hand, even though TRIP steel shows the excellent energy absorption under the high-speed deformation, the amount of martensite is very small by an influence of the heat generation with plastic transformation. In order to solve this paradox and explain macroscopic performances from the microscopic deformation mechanism, a concept of a spatio-temporal multiscale should be introduced. In this paper, research works done by the one of the authors on the mechanism of high functionalization in TRIP steel from the viewpoint of a spatio-temporal hierarchy are summarized with reviewing some related papers.