Papers by Keyword: Dynamic Deformation

Abstract: The paper presents microstructural and mechanical results of medium manganese steel deformed under high strain rates. The rotary hammer tests at strain rates of 250, 500 and 1000 s^-1 were applied. Mechanical properties under dynamic tensile loads were determined. According to the obtained results, when strain rate increased the yield point of the steel increased. An opposite trend was present regarding total elongation. In case of tensile strength, its level is similar for all analyzed deformation rates. The microstructure of the steel after the dynamic tensile test is composed of bainite, martensite and martensitic-austenitic islands. The strain-induced martensitic transformation was identified in microscopic investigations.

Abstract: Aluminum tubes are efficient energy absorbing components and are widely used in the automobile industry. In the previous report, the authors investigated the influence of cross-sectional shape on axially compressed aluminum tube by numerical analysis. However, there are only a few reports on length of aluminum tube. This paper deals with the influence of axial length and reinforcing rib on dynamic axially compressed aluminum polygonal tube in order to obtain the basic data of buckling and impact resistance. A numerical analysis of the dynamic deformation process of the polygonal tube was made with a finite element method. The result shows that even if the axial length was changed, there was no difference in the trend of the load-displacement curve in each cross-sectional shape. However, the maximum load part on load-displacement curve was changed. The buckling was generated partially and the deformation was larger at the corners in each axial length and cross-sectional shape.

Abstract: Dynamic deformation of metals in the elevated strain rate interval of elastic-plastic wave propagation is relevant to technological conditions, such as structural response to impact, ballistic effects, and metal forming processes. In the present work, the work hardening of quasi-static and dynamically deformed copper using a split pressure bar was evaluated for two different grain sizes. From slip lines observations in conditions of both dynamic and quasi-static strain rates, as well as an insensitivity to grain size of the yield stress, it is suggested that copper behave like a single crystal under dynamic deformation. It is shown, for the first time, that the work hardening rate during dynamic deformation of polycrystalline copper remains higher up to the fracture.

Abstract: In this paper, the dynamic deformation and rupture of pre-notched thin metal plates subjected to confined blast loading were investigated. The thin copper plates with cross-shape pre-notch were clamped on the end of a confined cylinder vessel by a cover flange. An explosive charge with a mass of 4g was detonated in the vessel center to generate blast load acting on the metal plates. The images of metal plates were recorded by two high-speed cameras. The displacement and strain fields during the deformation and rupture process were measured by using 3D digital image correlation (3D DIC). The effects of pre-notches on the dynamic deformation and rupture of thin metal plates were analyzed. The microstructure of fracture surface was examined The 3D DIC technique is proven to be an effective method to conduct dynamic full-field deformation measurement.

Abstract: The high temperature deformation and fracture behavior of ultra-high strength G33 steel under high strain rate compression are investigated by means of a split Hopkinson p ressure bar. Impact tests are performed at strain rates of 1000/s and 2200/s and at temperatures ranging from 25°C to 700°C. The SEM and TEM techniques are also used to analyze the microstructure evolution of the adiabatic shear band (ASB) and fracture characteristics of the deformed specimens at high temperature. The experimental results indicate that the flow stress of G33 steel is significantly dependent on temperatures and strain rates. The flow stress of G33 steel increases with the increase of strain rates, but decreases with the increase of temperatures. The strain rate sensitivity is more pronounced at the low temperature of 25°C. In addition, G33 steel is more liable to fracture at high temperatures than at 25°C. Observations of microstructure show two well-developed symmetric parabolic adiabatic shear bands on the longitudinal cross-section of the cylindrical specimen deformed at the temperature of 700°C and at the strain rate of 2200/s. Within the ASB, the width of the fine equiaxed grain structure is about 7μm. The size of those equiaxed grains is approximately 100nm. The fracture analysis results indicate that the ASBs are the predominant deformation and the specimens fracture along adiabatic shear bands. The fracture surfaces of the deformed G33 steel specimens are characterized by two alternating zones: rough dimple zone and relatively smooth shear zone. Further observations reveal that smooth shear zones consist of severely sheared dimples.

Abstract: In order to obtain high dynamic RMS performance of the scanning mirror in the working condition, the topology optimization method based on the constrain of dynamic deformation was carried out. Effective simplifications are implemented to reduce the complexity of the calculation. With the topology method, a lightweight form of the scanning mirror was generated on the dynamic working condition. The result shows that the lightweight ratio of the optimized structure is 47.4%, the PV value is 19.36nm and the RMS value is 5.65nm, which is improved by 18.46% and 17.41%, respectively. Besides, the first order frequency has increased by 113.8Hz. The results illustrate that the proposed method for the optimization of the scanning mirror is reasonable and practically.

Abstract: Investigations on dynamic deformation behavior of metallic materials under high strain rate have been conducted. In this study, the deformation behaviors of metallic materials with different crystal structures were examined through Taylor impact test. As representative materials, HSA800 (body-centered cubic: BCC), OFHC (face-centered cubic: FCC) and Ti-6Al-4V (hexagonal close-packed : HCP) were adopted. Taylor impact tests were carried out in the impact velocity range of 100~270 m/s for BCC and FCC materials and 150~330 m/s for Ti-alloy one. In addition, an 8-Ch high-speed photography system was used to provide a series of images representing the plastic deformation behavior of a projectile during Taylor test. The dynamic yield strength and the strain rate were calculated based on the contact time duration of projectile determined from high-speed images. From the result, the strain rate dependency of the dynamic yield strength varied depending on the material adopted. Bulging occurred at the impact part was more significant in FCC material than in BCC one, while a shear band occurred in the Ti-alloy specimen when the impact velocity of projectile exceeded 270 m/s.

Abstract: Equal channel angular pressing (ECAP) has been widely used for grain refinement in many alloys. In this article, the major emphasis was on the effect of grain size, temperature and strain rate on dynamic behavior of ECAPed AZ31. The dynamic mechanical properties of 6 pass and 8 pass ECAPed AZ31 were tested by split hopkinson pressing bar (SHPB) at wide temperatures range. At dynamic loading conditions, the ECAPed AZ31 shows strong strain hardening properties. The strain hardening rates decrease due to more slip systems’ opening with the increase of temperature. With the grain refinement, the fine-grain size and temperature show strong effect on the strain rate sensitivity.

Abstract: The dynamic mechanical property and microstructure evolution in localized shear deformation was investigated in the Al-5.6%Mg-0.75%M-0.25%Er alloy cold rolled to 80% reduction by using Gleeble 3500 compression at the strain rate of 0.01~500s^-1. The results show that both a critical strain rate and strain were required for the formation of local shear band under high strain rate compression. The initial Lamellar Boundaries (LBs) in the matrix region are parallel to the rolling direction (RD), with average boundary spacing of 0.25μm; The LBs within the shear bands region have a angle of 20° with RD, whose boundary spacing is ranging from 0.1 to 0.2μm. The LBs gradually rotate to an angle of 20° with RD and finally become wavy shape during the dynamic deformation.

Abstract: Double loop cutters arrangement can settle the contradiction between rotational inertia of the tool magazine and the dimension limitation of the cutter head effectively, and increase the store of tools. Disc type tool magazine with double loop cutters arrangement is designed and researched. The spring steel 65Mn is used to manufacture elastic cutter fixture as the holding device for its inner and outer loop tools. The dynamic deformation of elastic cutter fixture is discussed. The entire geometric movement process of elastic cutter fixture from being opened by the tool holder to accomplishing the whole action is analyzed. The effect and trend of inner stress caused by geometric deformation are studied. Furthermore, the force condition in each part of tool fixture can be calculated, thus predicting the motion stability and reliability of the elastic cutter fixture, and providing theory references for the design of elastic cutter fixture.