Key Engineering Materials Vols. 535-536

Abstract: In this research, micro void behavior of DPS, which has different phase volume fraction, is investigated experimentally. Prepared specimens have different amount of alloy element and heat treatment condition. Although both these specimens have almost the same strength and total elongation, these showed quite different local elongations, hole expanding ratio and bending ductility. In order to observe micro void behavior specimens, that have different strain levels, are prepared. These sectional areas are observed by laser microscope after cutting and polishing. The change ratio of micro void volume fraction of DPS, which showed high local ductility, is lower than that of the other DPS. Concerning low ductility DPS, small size void (less than 3µm diameter) increases rapidly not only at grain boundary but in the ferrite grain, especially at initial stage of deformation. On the other hand, nucleation of micro void of high ductility DPS is inhibited.

Abstract: In this study, distributions of microscopic stress at free edges of unidirectional carbon fiber-reinforced plastic laminates (CFRP laminates) are analyzed three-dimensionally, based on a homogenization theory for time-dependent composites. For this, the homogenization theory is reconstructed for free edge problems using a traction-free boundary condition. Then, an analysis domain is reduced using the point-symmetry of the internal structure of the unidirectional CFRP laminate. Moreover, the substructure method is newly introduced into the theory to reduce the computational costs required for the analysis. The present method is then applied to the elastic-viscoplastic microscopic stress analysis at free edges of unidirectional carbon fiber/epoxy laminates subjected to an in-plane uniaxial tensile load. It is shown that complex microscopic stress distributions occur in the vicinity of the free edge, especially around fiber/matrix interface regions.

Abstract: The homogenized elastic-viscoplastic behavior of thick perforated plates with pore pressure is investigated for macro-material modeling. To this end, the homogenized behavior is analyzed using a FE homogenization method of periodic solids. It is assumed that the base metal of perforated plates exhibits the elastic-viscoplastic behavior based on Hooke’s law and Norton’s power-law. The resulting homogenized behavior is simulated using an elastic-viscoplastic macro-material model developed for pore-pressurized anisotropic open-porous bodies. It is shown that the macro-material model suitably represents the macro-anisotropy and macro-volumetric compressibility that are revealed by the FE homogenization analysis in the presence and absence of pore pressure.

Abstract: The objective of this work is to study the large deflection of a pin-supported slender geometrically asymmetric metal foam core sandwich beam under transverse loading by a flat punch. Based on the yield criterion for geometrically asymmetric metal foam core sandwich structure, analytical solution for the large deflection of a pin-supported slender sandwich beam is obtained, in which the interaction of bending and stretching induced by large deflection is considered. The finite element results confirm the accuracy of the analytical solutions. The effects of asymmetric factor and boundary condition on the structural response of the asymmetric sandwich beam are discussed in detail. It is shown that the axial stretching induced by large deflection plays an important role in the load-carrying and energy absorption capacities of geometrically asymmetric sandwich structure.

Abstract: The collapse modes and energy absorption in three-point bending of composite sandwich beams were explored experimentally. Sandwich beams manufactured from woven carbon fibre face sheets encapsulating aluminium foam cores were investigated at 0.001 s-1 and 100 s-1 strain rates. Three modes of failure were observed during deformation: Modes H1, H2 and H3. The direction of core shear played an important role in the energy absorption of the structure. Mode H2 gave rise to the highest specific energy absorption of the composite sandwich beams studied.

Abstract: Angled sandwich core made of thin aluminium sheets was analysed numerically to investigate their mechanical performace under various loading conditions. The stress distribution and deformation were compared with conventional hexgonal honeycomb cores of same relative density under various loadings. Possible failure modes are observed. The finding helps to provide a guidance to the design of ligthweight armour against explosive loading.

Abstract: In this paper, the effect of material characteristics on plastic forming of adhesively bonded dissimilar sheet metals was investigated by experiments and finite element method (FEM). The acrylic adhesive employed in the experiments has visco-plasticity characteristics with high ductility and strong strain-rate and temperature sensitivity in strength. Major results obtained are summarized as follows: (1) In the adhesively bonded dissimilar sheet metals, the gull-wing bend and the shear deformation of the adhesive layer are suppressed by the combination of the sheet metals when a bending inside sheet has high-tensile strength. (2) The gull-wing bend is suppressed by high-speed forming at a lower temperature as well as the same kind of sheet metals. (3) The calculated results using MSC Marc2010 are relatively good agreement with the experimental results.

Abstract: The crush behavior of aluminum hexagonal honeycomb with perforated cell walls under out-of-plane quasi-static loadings was experimentally investigated. The honeycomb specimens with different heights were compressed in axial direction under displacement control. There are four sequential deformation stages during compression: linear elasticity, buckling, crushing and densification state. The performances of hexagonal honeycombs with perforated cell walls were compared with those of imperforated hexagonal honeycombs with the same sizes. The results show that the perforated holes weaken the strength of honeycombs markedly and the strength of honeycomb decreases with the specimen height.

Abstract: CFRP composite with light weight, high strength, and high elasticity compared to metal is widely used rather than previous steel plates. However, CFRP composite material has the weakness in hygrothermal and impact collapsed environment. Especially, moisture absorption into composite material under hygrothermal environment can change molecule arrangement and chemical properties. Therefore, the purpose of this study lies in acquiring quantitative design data that can be put into the practice by comparing and evaluating the strength degradation under the environment where the moisture is absorbed by conducting static and impact collapse test after setting extreme condition for CFRP composite that takes consistent form such as frontal side members that is actually used in vehicle. This study compared and studied change in the progress of a moisture absorption ratio after setting up the temperature of 60 degrees, and 80 degrees in order to comprehend how the change in the temperature impacts on moisture absorption status inside CFRP composite materials. As a result of this study showed that the strength reduction of about 50% appears due to moisture absorptions. In addition, it showed that the higher the temperature is, the more rapid the progress of a moisture absorption inside CFRP composite materials is. Accordingly, it showed that the change in matrix also has a weak point.

Abstract: Injection molding process one of the most important methods to produce plastic parts with high efficiency and low cost. Today, Injection molded parts have been increased dramatically the demand for high strength and quality applications. In this study, truck brake pedal is made of Cast iron and plastic materials to replace the frame for the optimization process that minimizes the runner and the gate dimension will determine the size and shape. Runner and gate dimensions of change based on availability of the product. I will discuss the injection molding. This report investigates that the optimum injection molding condition for minimum of runner and gate position. The FEM Simulation CAE tool, MOLDFLOW, is used for the analysis of injection molding process.