Papers by Keyword: Fracture Process

Abstract: A cementitious system embedded in microcapsules can achieve self-healing, and the fracture and triggering behavior of microcapsules is with great importance. In this study, the crack behavior of the concrete-microcapsule system was simulated by a three-dimensional lattice model. Based on the results of the fracture energy test on concrete beams and the nanoindentation test on microcapsules, the local mechanical properties of the lattice elements were determined. The aim of this paper is to set up a three-dimensional lattice model to study the trigger mechanism of the microcapsule-interface-concrete zone.

Abstract: Recent research in the process of die casting production of aluminium alloys which are nowadays deeply implemented in the rapidly developing automobile, shipping and airline industry aims to increase the manufacture and quality properties of the casting in order to obtain its high mechanical properties at acceptable economic costs. In terms of ensuring the quality indicators in the production of aluminium castings it is necessary to pay close attention to internal structural quality of the castings characterized by type and extent of foundry defects (cavities, Al₂O₃ particles, internal cold laps). The presenting contribution deals with the analysis of the fracture process, the microorganism disturbance of test samples, the impact of casting speed on the occurrence and extent of the castings porosity and reasons for the internal foundry defects of casting alloys EN 43100 manufactured by die casting technology.

Abstract: Polypropylene fiber reinforced concrete (PPFRC) is such a composite material that can enhance and improve the mechanical property of the concrete with small mixing amount of polypropylene fiber. By taking into consideration the heterogeneous characteristics of materials at meso-scopic level, the initiation of micro cracks, the propagation and the coalescence between cracks have been simulated in PPFRC specimens with different amount of addition under three point bending load. The numerical analysis shows that there is only little difference on failure pattern and path between PPFRC and plain concrete. However, polypropylene fiber can reduce or even eliminate plastic cracking and can help to control crack expansion and it could be identified that most fibers in PPFRC are broken under tensile stress. Furthermore, polypropylene fiber plays different roles during the substrate plastic shrinkage and hardening stages. The toughness and deformability have been significantly improved with mixing of polypropylene fibers but the rupture strength is almost the same. Meanwhile, it also could be found that, with the increasing amount of polypropylene fiber, the deformation ability and the toughness have been increased, but the strength is kept almost the same, while the elastic modulus is actually decreased.

Abstract: During forging of as-cast for fractured connecting rod, the key is to determine heating temperature and to control cooling speed after forging. They two points are correlated with each other. To assure metal fluidity in the course of striking and forging, fillet should be enlarged at transit between ribs and web. Wrought parts shall be subject to normalizing by residual heat from forging process. Its metallographic structure consists of pearlite and ferrite. Content of ferrite should not exceed 35%. In addition, it should be such that the fraction for volume of ferrite get bigger and grain should be greater and evenly distributed.

Abstract: In this paper, the fracture process of WCp/Cu functionally graded materials(FGMs) was investigated. The used materials were fabricated by powder metallurgy using tungsten carbide(WC) particles and copper(Cu) matrix, and had functionally graded layers. In order to investigate the fracture process of the FGM, three-point-bending tests of rectangular specimens were carried out. From the results, it can be seen that the bending performance of FGM structures with increasing WC content from head layer to the bottom layer excels that of FGM structures with decreasing WC content in three-point-bending tests.

Abstract: For the Three Gorges granite, a finite difference software package FLAC was used to study failure process of heterogeneous rock material. Based on mineral components identification results of the granite and fuzzy clustering method, the actual image date was transformed into the finite difference grid by applying image processing techniques. A convenient and efficient two-dimensional numerical modeling method for heterogeneous geomaterials was presented. Then, failure process of the granite were simulated in uniaxial compression test based on experimental strain soft model, and the stress concentration phenomenon was analyzed. The results show that the numerical modeling method based on digital image processing can be used to calculate the mechanical responses of geomaterials by taking their heterogeneities into considerations.

Abstract: In this paper, in situ observation of fracture process of short carbon fibers/epoxy (SCF/EP) composites was researched. The samples were prepared firstly. And then, in order to get high quality reconstruction images of carbon fiber–epoxy composites, experiments of in situ static observation of SCF/EP composites were carried out. As results, static 2D and 3D reconstruction images of fiber-epoxy composites were obtained. At last, a special small tensile testing device which can be used to apply extraneous force to small samples was designed. Based on the above work, in situ observation of fracture process of composites will be realized most probably in the next work.

Abstract: This study was investigated the evolution of fracture damage of reinforced concrete (RC) beams strengthened in flexure with carbon fiber-reinforced polymer (CFRP) sheets or plates using acoustic emission (AE), and developed an AE monitoring strategy that can determine the structural integrity of RC beams strengthened by external bonding of CFRP sheets or plates. In this study, five beams were used, each with a cross sectional area of 200300 mm2 and length of 2,000 mm. Each specimen was simply supported and subjected to three-point loading. The AE signals were monitored during flexural testing of specimen using four sensors located on the side of each beam. The damage behavior and the microscopic fracture process of the RC beams strengthened with CFRP was evaluated using the AE parameters, such as AE duration time, event and amplitude. The two-dimensional AE source location was successful in measuring crack initiation and propagation in the RC beams strengthened with CFRP.

Abstract: Combining in-situ tensile tests with detailed observations of fracture surfaces of a two-phase TiAl alloy, the fracture process and fracture mechanisms of TiAl alloys are investigated. The results reveal that Cracks prefer to initiate and propagate along lamellar interfaces, which are the weakest link in the near fully lamellar microstructure. The interlamellar strength calculated is less than the translamellar strength. The tensile stress is the driving force for crack initiation and propagation. In specimens with a slit notch, most cracks are initiated directly from the notch root and extended along lamellar interfaces. The main crack can be stopped or deflected into a delamination mode by a barrier grain with a lamellar interface orientation deviated from the direction of crack propagation. In this case, new cracks are nucleated along lamellar interfaces of grains with favorable orientation ahead the barrier grain. The main crack and a new crack are then linked by the translamellar cleavage fracture of the barrier grain with increasing applied load. In order to extend the main crack, further increases of the applied load are needed to move the high stress region into the ligament until final fracture. The process of a new crack nucleation with a bridging ligament formation decreases the crack propagation resistance rather than increases it.

Abstract: Fracture behavior of fully lamellar (FL) and duplex phase (DP) TiAl alloys is reported in this paper. It was found that the inverse behavior of coarse FL TiAl alloy showing inferior tensile properties but superior fracture toughness resulted from the different fracture mechanisms of these two types’ tests. In tensile specimens, the final fracture happened at a section that was most heavily damaged by the accumulation of large interlamellar microcracks and arbitrarily located within the gauge-limited volume. In 3PB notch specimens, the propagation of the main crack was constrained within a narrow strip nearby the centerline where the normal stress was the highest. Large lamellar grains caused serious damage in tensile tested specimens. However multi-oriented large lamellar grains formed seriously bifurcated crack tips, which made the crack propagation more difficult in 3PB notched specimen. The main mechanisms of toughening in FL specimens were the deflection of main crack, bifurcation and blunting of crack tip and formation of a diffuse zone of microcracks. These phenomena reduced the driving force for crack extending and then increased the fracture toughness.