Papers by Keyword: Failure Behaviour

Abstract: Failure behaviour of aircraft sandwich panels under bending load has been investigated in this study. Three-points bending test was performed to the specimens with various span-to-thickness (S/d) ratios 32, 40, and 60. Testing method and dimension of specimens were adhering to the American Society for Testing and Materials (ASTM) D-790M. Deflection and energy absorption of the sandwich panels was characterized by specific span-to-thickness (S/d) ratios. It was found that specimen with S/d of 40 has the steepest slope in stress-strain curve and specimen with S/d of 32 has the highest flexure strength, 831MPa. The flexure strength decreases with the increasing of span-to-thickness ratio. The result shows that the increasing of the span-to-thickness ratio increased the crack length at the lowest maximum bending stress, 636 MPa. The results suggest that the performance of the Carbon Fiber Reinforced Epoxy (CFRE) composites is strongly influenced by the crack length.

Abstract: Aerodynamic gun impact test is carried out to investigate sandwich beam with metallic skin and Nomex honeycomb core damage mechanism and failure behaviour. Details of the deformation and damage progression within the sandwich beam are observed in particular. The comparisons between the two kinds of specimen with different thickness skins clearly show that the difference in the impact energy consumed in global bending deformation and the localized indentation. Theoretical elastic bending stiffness of the sandwich beam with thicker skins is approximately 2.26 times greater than that of sandwich beam with thinner skins.

Abstract: A type of quasi-isotropic carbon/epoxy composites was prepared. In order to study the dynamic mechanical properties of composites, the compressive specimens were investigated in the normal direction, as well as in the in-plane direction at different strain rates by Hopkinson pressure bar (SHPB) technique. The macro- and micro-fracture morphology of the damaged specimens was obtained utilizing the scanning electron microscope (SEM). The experimental results showed that the dynamic stress-strain behaviour can be significantly affected by the strain rates. As the strain rates increased, the maximum strength and maximum modulus increased, the ultimate strain reduced. The compressive strength and the ultimate strain in the in-plane direction are obviously lower than that in the normal direction. The main way of the dynamic compressive failures in the normal direction is shear failure due to the brittle fracture of the fibre. Interfacial crack and delamination can be produced in the in-plane direction.

Abstract: A type of basalt fibers polymer functional composites embedded with ZnO whiskers was prepared. The as-prepared composites exhibited good microwave absorption properties after the dispersion of ZnO whiskers in resin. The dynamic compressive properties of composites were investigated by the split Hopkinson pressure bar (SHPB) system. The macro- and micro-fracture morphology of composites was obtained by the scanning electron microscope (SEM). The experimental results showed that the as-prepared composites have excellent mechanical properties, and the compressive properties could be significantly affected by the strain rates in the in-plane direction, as well as in the normal direction. As the strain rate increased, the higher strength and elastic modulus are obtained. Under the dynamic compressive load in the normal direction, the main failure mode of composites is pure compression. On the other hand, longitudinal splitting and delamination of composites could be induced when loaded in the in-plane direction. The micro- interfacial crack, fiber fracture and plastic deformation of resin could be observed from the morphology of fractured composites.

Abstract: In this study, failure behavior of hot gas casing for gas turbine was investigated. The microstructure and damage mechanism of serviced hot gas casing were examined. Also low cycle fatigue tests of the Inconel 617 super alloy is used for structural material of hot gas casing were performed. To predict the low cycle fatigue life, Coffin-Manson and strain energy density methods were used.

Abstract: There are numerous applications of pressure vessels in aerospace field for storing liquid or gaseous media. Generally the metallic vessels have been manufactured by welding two hemispheres, which are machined or spin-formed. In this study, the solid state bonding method was utilized with blow forming to manufacture aerospace titanium tanks. This solid state joining technology replaced the welding process and without any secondary material or liquid phases in bonding process, homogeneous microstructure was obtained at bonding interface. Using this method, a titanium tank of a space vehicle was manufactured and during a hydraulic pressurizing test, the strain and acoustic emission signals are observed to investigate the effect of solid state bonding method on the failure mode and performance of the tank.. This result was compared with the one made by conventional method of spin forming and welding. The result shows that the pressurization rate and the acoustic emission signal increasing rate provide a similar tendency for a vessel of integrity, while the signal increasing rate is much higher than the pressurization rate for a vessel with welding defects. It is clear that the failure mode of the solid state bonded tank is different from the welded tank due to the completely united interface by diffusion process.

Abstract: Submerged Entry Nozzle (SEN) are usually made from a combination of carbon bonded alumina, zirconia and magnesia with graphite, which have been found to give the best response to the extreme demands of thermal shock, corrosion and erosion resistance. SEN brittle fracturing and clogging is a serious productivity and quality problem in continuous casting. The SEN critical area of failure is the steel flange where the SEN neck is fixed. Thermal shock or mechanical stress may cause cracking, which can result in premature failure. Preheating on optimal temperature before SEN installation is the standard procedure. Thermal stress effect on fracture behavior was done by analyze of material fractography, morphology, macrostructure and microstructure.

Abstract: This paper presents the results of an experimental procedure where a grid is applied to the edge of a specimen and the local crack-tip displacement fields are calculated using finite element technique. Increasingly, the objective of finite element simulations is to predict the response of the mechanics of material failure are related to microstructural process that occur in the materials as a result of the loading conditions. At the same time, The influences of coating thickness, coating stiffness, and assume crack pattern on the stresses concentration between the neighbouring layers of material are evaluated. Consequently, one approach to simulating the response of structures is to explicity model the mechanisms of damage and failure in the material.