Papers by Keyword: Crack Bridging

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 paper deals with crack bridging modelling in Bioglass® based scaffolds due the presence of a special polymer coating. This includes a careful identification of bridging mechanism by polymer ligaments, selection of a suitable bridging model and its implementation into the gradient elasticity model of crack.

Abstract: Hybrid material systems are designed by the specific combination of different materials. As a result, expanded property profiles can be achieved, which would not be possible with monolithic material solutions. For lightweight, high strength and high rigidity, complex shaped structural components, which are used in the automotive industry and in aerospace, hybrid material systems offer an outstanding potential. A comprehensive understanding regarding the interaction of the individual components of the hybrid material is of great importance for a more efficient design of future structures. In this work, existing hybrid solutions for industrial applications and those, which are subject of current research, are analyzed and categorized first. Intrinsic and extrinsic material combinations are considered at different levels, ranging from hybrid laminates on shell level to complex hybrid structures on component level. Based on the situation analysis, different hybrid solutions are evaluated and compared considering the requirements of the automotive industry. Furthermore, the associated physical mechanisms which are responsible for the respective property profile are considered and explained systematically. The long-term objective of the work is to establish a methodology to derive the necessary physical mechanisms and, based on that, to derive optimal hybrid solutions for desired property profiles.

Abstract: A toughening model of crack bridging reinforced ceramic matrix composites is presented. It was shown that this transition closely relates to the extent of toughness, particle size or volume fraction, and the particle yield stress. The constitutive equation is obtained through micromechanical considerations based on crack bridging toughening. The results show that the model is in good agreement with SEM results.

Abstract: Wedge open loaded (WOL) specimens of age hardened Zeron 100 duplex stainless steel were tested in 3.5 wt % NaCl solution with cathodic polarizes applied at-900mV/SCE to investigate stress corrosion cracking mechanism in duplex stainless steel. The interaction between microstructure and mechanism of stress corrosion cracking was studied. Fracture mechanism was studied by using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The material was found cracked by ferrite cleavage, austenite tearing and austenite dissolution by environment. The ferrite cleavage took place along {100} planes and {112} twin habit planes. The austenite grains appear to act as crack bridging & crack arrester and failed by tearing & stress corrosion cracking.

Abstract: Epoxy composites reinforced with recycled cellulose fibre (RCF) have been synthesized and characterized. The reinforcement by RCF has resulted in a significant increase in the strain at break, fracture toughness and impact toughness but moderate increase in flexural strength and flexural modulus. The effect of seawater soaking on the flexural and impact properties has also been investigated. The micromechanisms of toughening and crack-tip failure processes are identified and discussed in the light of observed microstructures from in-situ and ex-situ fracture.

Abstract: Microstructure can have a significant effect on the resistance to intergranular stress corrosion cracking. Certain grain boundaries are susceptible to corrosion while others have high resistance and may form crack bridging ligaments as the crack deviates around them. To investigate the mechanics of crack bridging, 3D computational model has been previously developed. An extension to the model, to include stress corrosion crack growth kinetics is presented in this paper. An analysis of the effects of resistant grain boundary fraction demonstrates that the bridging ligaments can significantly retard short crack propagation rates. Increasing the fraction of resistant boundaries is shown to improve microstructure resistance by reducing the crack propagation rate.

Abstract: Epoxy ecocomposites reinforced with recycled paper (rP) and nano-kaolinite (nK) have been synthesized. The effect of seawater soaking on the flexural and impact properties have been characterized. This new but cost-effective approach has been developed to improve the physical and mechanical properties of polymeric materials without adversely affecting their processing characteristics. The micromechanisms of toughening and failure processes are discussed.

Abstract: The objective of this study is to investigate the tensile behavior and fracture toughness of glass fiber reinforced aluminum hybrid laminates (GFAL) in association with the fracture process using plain coupon and single-edge-notched specimens. The tensile properties of GFAL, such as elastic modulus and ultimate tensile strength, were clearly dependent on the fiber orientations. In particular, the superiority of GFAL0 in KIC and GIC was much more pronounced than that of monolithic Al 1050. However, a transverse crack parallel to the fiber orientation reduced the toughness of GFAL considerably. Microscopic observations of the fracture zone in the vicinity of the crack tip exhibited various modes of micro-fracture in the respective layers as well as fiber fractures and interface delamination between fiber composite and Al layers. Such a damage evolution in GFAL depending on the fiber layer orientation had strongly influence upon the tensile behavior and the toughness of GFAL.

Abstract: In this paper the bridging action of steel fibres on the model I crack propagation has been studied experimentally for steel fibre reinforced concrete (FRC). From the experimental results three main conclusions are obtained. First, the bridging action increases with the number of the steel fibres across the crack surface and the stress intensity factor near the crack tip decreases thereby. Second, bridging action increases with the strength of the matrix because the matrix with higher strength can provide stronger interfacial bond with steel fibres. Third, the interfacial bonding gets damaged when the steel fibres under cyclic loads and the bridging action degrades with the cycle number.