Papers by Keyword: Fracture

Abstract: In this work, the effect of the laser shock-wave treatment on the surface morphology and regularities in failure of nanotitanium is investigated. Based on the data of fractodiagnostics it is established that the shock-wave treatment changes the mechanism of failure from the brittle chipping to the mixed ductile-brittle one by the shear + separation scheme.

Abstract: For the description of the behavior of anisotropic materials within the framework of the phenomenological approach the model which is taking into account distinctions in strength on compression and a stretching is offered. The model as allows carrying out researches with any orientation of properties of a material concerning system of coordinates. Numerical modeling is carried out in three-dimensional statement. The range of velocities of interaction up to 3000 m/sec is considered.

Abstract: Periodic cellular metals (PCMs) based on lattice truss structure have been developed for a wide range of potential applications with their lightweight and multi-functionality. Although divers methods to fabricate truss PCMs, such as investment casting, perforation-bending, and extrusion-EDM, have been reported, the processes have been limited to fabricate flat plates. The paper proposes a new method, multiple pin stretch forming, to fabricate the truss PCM with various cross-sectional shapes. The process has some advantages to fabricate the truss architecture with locally different height and reduce the waste of material during perforation process compared with conventional processes. However, since a 3-D truss structure is built up by tensile deformation of truss members in the process, it is important to design the geometry of precursor sheet to avoid unexpected fracture and make full use of elongation of a given material. The paper focused on the design of precursor sheet through the investigation on failure limit in multiple pin stretch forming. The forming failure were predicted by FE simulations combined with a ductile fracture criterion for various geometrical conditions, and a forming failure diagram was constructed and verified with experiments. And finally, pyramidal truss PCMs with flat and stepped cross section were fabricated successfully without any defects.

Abstract: Alumina dispersion hardened copper-base composite was fabricated by internal oxidation method. The high temperature tensile fracture of Cu-Al₂O₃ composite was studied and tensile strengths were determined at different temperatures of 600, 680 and 780 °C. Microstructure was investigated by means of optical microscope and field emission scanning electron microscope (FESEM) with energy dispersive spectroscopy (EDS). Results show that, ultimate tensile strength and yield strength of copper alumina nanocomposite decrease slowly with increasing temperature. The yield strength reaches 119 MPa and ultimate tensile strength reaches 132 MPa at 780 °C. Surface fractography shows a dimple-type fracture on the fracture surface of the tensile tests where dimple size increases with increasing testing temperature and in some regions brittle fracture characteristics could be observed in the fracture surface.

Abstract: We sum up the reservoir space types and characteristics of clastic rock reservoir ShiWu fault depression rift layer study area, through core observation, microscope, scanning electron microscope and mercury injection methods, and discuss the development characteristics and formation mechanism of pore and fracture. A large number of core analysis, drill results and test mining research has confirmed that the study area is constructed by the strong force, the micro-cracks are well developed, it is not only important reservoir space, but also the flow of oil and gas wells to obtain high yield important seepage paths, is to obtain yield the necessary conditions.

Abstract: Specific features of plastic deformation and tensile failure of a spring steel with systematically various pearlite fineness obtained by isothermal transformation have been investigated by uniaxial tensile tests and electron microscopes. The results indicated that pearlite interlamellar spacing has an important influence on that. The tensile fracture surface is consisted of the center plastic fracture region and the edge brittle fracture region while the interlamellar spacing is within the range 140-280nm, and is a completely brittle fracture and no necking with the further increase in interlamellar spacing to 510 nm. The deformation characteristics of pearlite in the neck regions is mainly including S-shape bend, rotation and shearing. And the data obtained suggest that the interlamellar spacing within 140-280nm can ensure the plasticity for the steel.

Abstract: The mode-I fracture of adhesive surface was studied by uniaxial tensile test of the double cantilever beam (DCB) adhesive joints which were made from aluminium sheet and Hydroxyl-terminated polybutadienec (HTPB). The load - displacement curves which characterize the response of the macroscopic fracture show a significant rate-dependent property, i.e. the peak load and corresponding displacement increase with the increase of the loading rates. The critical energy release rate has been defined in two waysnon-linear initiation point (NL) and the maximum load point based on the experimental curves, was gained by the corrected beam theory of fracture mechanics. In addition, the cohesive parameters-fracture energy was also decided by the inversion identification method. The fracture energy obtained numerical simulation is slightly greater than the value obtained by the corrected beam theory, but both results indicate the fracture energy of the adhesive interface also increases continuously with increasing loading rates.

Abstract: An experimental study on wear and fracture of ball-end milling cutter in high speed machining martensitic stainless steel 0Cr13Ni4Mo is studied in this work. Through the SEM micrographs and energy spectrum analysis of the wear pattern of the rake face, severe coating spalling is found near the main cutting edge. Fracture is seen on the entire cutting edge, in which micro-chipping occurs on the both ends of the cutting edge, and chipping occurs in the middle of the cutting edge and is the conchoidal spalling on the rake face. Combined with the high-speed photography of the milling process, the fracture area is consistent with the chip-adhesion area.

Abstract: Based on the understanding of material characteristics and interaction between projectile and target, a lightweight hybrid composite armor target consisting of alumina ceramics pellets and ultrahigh molecular weight polyethylene (UHMWPE) was designed and prepared. The target areal density of the armor panel was 7.5 g/cm². The standard size of the armor panel was 150mm×150mm×43mm. The Ballistic Performance of Alumina/UHMWPE composite armor against an impact of 12.7 mm armor piercing (AP) projectile was investigated at the nominal velocity of 818 m/s. The energy absorbing mechanism revealed that the armor was able to protect against the projectile, together with weight saving.

Abstract: To provide the doctors a basis for treating sacral fractures and offer optimal surgical program, three-dimensional (3D) finite element method was used to simulate normal pelvis and the unstable pelvis sufferedIsection, IIsection and III section sacral fracture respectively.The unstable pelvises were respectively fixed with five different internal fixation implants types, which are respectively rectangular plate with cannulated screw, rectangular plate with solid screw, expansile bolt, convex plate with cannulated screw, convex plate with solid screw. The stress distribution and the X, Y, Z direction displacement of the sacrum were calculated for each sacral fracture treatment of five internal fixation implants after giving 500N axial load on lumbar vertebra and were compared with the normal pelvis, then the optimal surgery program were determined. After the analysis, by comparing the five combinations for each sacral fracture treatment of five internal fixation implants, the preferred combinations for the reset treatment of theIsection sacral fractures were rectangular plate with cannulated screw and convex plate with cannulated screw; The preferred combination for the reset treatment of the II section sacral fractures was expansile bolt; The preferred combination for the reset treatment of the III section sacral fractures was convex plate with cannulated screw.