Papers by Keyword: Toughening Mechanism

Abstract: Effect of Ti (C,N) based cermets granule on the microstructure, mechanical properties, sintering and fracture behavior of Ti (C,N) based cermets was investigated. Results show that the Ti (C,N) based cermets granules distribute in the matrix homogeneously. A nanoindentation study was performed on hard phase and binder phase in the matrix and granule. With the increase of granules content, sintering properties is worse. With the increase of granules content, transverse rupture strength (TRS) and relative density decrease gradually, while the hardness has an opposite trend. The fracture toughness increases firstly with increasing granule, and then decreases with the further increase of granules. Higher fracture toughness of the cermets is mainly owing to the crack branch and higher fracture energy of coarse granule.

Abstract: When blending rubbers into polymers, different rubber distribution status and fraction due to different mechanical property. In this research, effective mechanical properties of rubber-toughened polymers with four blending fraction in six kinds of particle distribution status are simulated numerically by using finite element method. Rubber particle distribution model include four 2D models and two 3D models. Typical effective mechanical properties such as yield stress, Young's modulus, Poisson's ratio and stress-strain curve of each status are obtained. The Results show that all models Young's modulus and Poisson's ratio decrease with rubber particle volume fraction increasing. Young's modulus and Poisson's ratio of three-dimensional body-centered cubic and face-centered cubic models are in a close magnitude range, it means rubber particle volume fraction has less effect on 2D models and two 3D models. As we all known, Matrix yielding, crazing and interface debond. All play an important role in the toughening process of rubber-toughened polymers. So in this paper we also study on toughening mechanism using same models. Our simulation takes use of stress concentration factor, yield ratio and interface elements' strain difference which is related with matrix yielding, crazing and interface debond to study the toughening mechanism. Simulation shows that the maximum stress concentration factor increases with particle volume fraction. The shear yielding occurs first at the equator of rubber particle, and then yield region expands from the equator to the pole of the particle with loads increasing.

Abstract: The main drawback still impairing the use of bioactive glasses in load-bearing applications is their intrinsic brittleness. The addition of coating constituted by polyvinyl alcohol (PVA) and microfibrillated cellulose (MFC) PVA/MFC led to a 10 fold increase of compressive strength and a 20 fold increase of tensile strength in comparison with non-coated scaffolds. Crack bridging by polymer coating was identified by fractographic observations as a main toughening mechanism. In this contribution a detailed computational analysis of crack bridging due to coating film fibrils is presented and an improvement of fracture resistance of coated scaffolds is explained.

Abstract: The shell structure YAG composite powders with different volume fraction (15, 20 and 25vol%) micro h-BN have been prepared by co-precipitation process. The bulk composites were performed by pressure sintering at 1600°C under a pressure of 30MPa in vacuum. The mechanical properties (elastic modulus, hardness, and fracture toughness) and relative density of the composites were investigated detailedly. Furthermore, phase composition and microstructure of the composites were analyzed thoroughly by X-ray diffraction, scanning electron microscopy. Meanwhile, good machinability is maintained due to the low hardness of the second phase.

Abstract: Laminated Ti-TiBw/Ti composites behave a moderate loading capacity and high fracture ductility with non-castropic failure stage under three-point bending test. Fracture characteristics of laminated composites reveal many extrinsic toughening behaviors, such as, interfacial delamination, bucking and crack deflection, and the interfacial delamination is attributed to the weak bonding strength. Many strengthening and toughening mechanisms are presented in the TiBw/Ti composite layer, such as de-bonding effects of TiB whiskers, multi-fracture of TiB whiskers, crack trapping effect and crack bridging effect.

Abstract: This paper presents the synthesis of a new type of flexible epoxy curing agent and an approach to improve the toughness of epoxy resin by curing without reducing the strength and modulus of the resin-cured material. The results show that the degree of toughness reaches maximum values when the flexible curing agent is applied at weight percentages (wt.%) between 10% and 15%. When the amount of flexible curing agent added to epoxy resin weight is 10wt.%, the impact toughness and fracture toughness increases by 33.3% and 96.3%, respectively, compared with the pure epoxy resin. When the amount of flexible curing agent added to epoxy is 10wt.%, the resulting impact thoughness of the material is 19.5 kJ•m-2 at-50°C, the impact toughness of pure epoxy resin is only 7.96 kJ•m-2.

Abstract: The analysis is made for the modification of multi-walled carbon nanotubes and the mechanical properties and microstructure of the modified carbon nanotubes toughening DSP cement mortar, the existence and toughening effect of modified carbon nanotubes on the fracture surface of materials were analyzed. Results shows that, the surface of the carbon nanotubes in the sample is covered with cement hydration products, with the carbon nanotubes in drawing state on the fracture surface and both ends of the tube connected firmly with cement materials, thus carbon nanotubes improve the toughness of materials effectively.

Abstract: Yttria-stabilized zirconia (YSZ) reinforced with multi-walled carbon nanotubes (MWCNTs) is fabricated through spark plasma sintering (SPS). Raman spectroscopy corroborated that MWCNTs survived the harsh sintering process. The MWCNT/YSZ composite exhibits ~ 34% improvement in fracture toughness as compared to YSZ. Grain refinement, MWCNT pullout and crack bridging are the major toughening mechanisms.

Abstract: This paper investigates the tensile properties and fracture toughness of a liquid rubber-modified highly crosslinked epoxy cured using 4,4 diaminodiphenyl sulphone (DDS/LR). The results for DDS/LR epoxy in relation to rubber and matrix properties are also compared with those of rubber-modified lowly crosslinked epoxy systems, namely, liquid rubber-modified piperidine cured epoxy (Piperidine/LR) and core-shell-rubber modified piperidine cured epoxy (Piperidine/CSR). It was found that highly crosslinked DDS/LR epoxy has a higher tensile strength than that of either Piperidine/LR or Piperidine/CSR epoxy, while it shows only a moderate increase in the fracture toughness.

Abstract: MWCNTs/Ti(C, N) cermets-based composites were prepared by vacuum hot-pressing sintering method. The mechanical properties of samples were examined. XRD and SEM were used to investigate the crystal structure of the composites and microstructure of fractures surface, respectively. The toughening mechanism of composites was discussed particularly. The experimental results showed that the optimum comprehensive mechanical properties of samples were obtained by adding 1wt% MWCNTs in the composites. The bending strength, Vickers hardness and fracture toughness of the composites were 1275.14MPa, 22.75GPa and 10.60MPa•m^1/2, respectively, which were improved by 16.89%, 17.15% and 25.59%, respectively, compared to the Ti(C, N)-based cermets without MWCNTs. Bridging and pulling out of MWCNTs, crack deflection, residual stress toughening and micro-voids toughening were attributed to the toughening mechanism of the composites.