Papers by Keyword: Interfacial Debonding

Abstract: A finite element model on the single fiber pull-out test of short fiber reinforced rubber matrix sealing composites (SFRC) were established. The effects of the interphase properties on the interfacial stress distribution and initial debonding strain are investigated based on the cohesive zone model (CZM). The influences of interphase thicknesses and elastic modulus on the interfacial debonding behavior of SFRC are obtained. The results show that the interfacial initial debonding strain increases with the increasement of interphase thickness, and it decreases with the increasement of interphase elastic modulus. An interphase thickness of 0.4 μm and an interphase elastic modulus of about 750 MPa are optimal to restrain the initiation of the interfacial debonding.

Abstract: Fiber reinforced cementitious matrix (FRCM) composites have recently become a hot topic in Europe as an alternative to traditional fiber reinforced polymer (FRP) composites for several strengthening applications of existing masonry buildings. The terrific success of this new retrofitting system is mainly due to some advantages that it offers when compared to FRP, such as the possibility of application of the composite to wet surfaces and the vapor permeability featured by the inorganic matrix. In this work, the stress transfer between FRCM composites and a masonry substrate is investigated. FRCM strips comprised of ultra-high-strength steel fibers embedded in a cementitious grout are externally bonded to masonry blocks. Single-lap direct shear tests are performed. Parameters studied are bonded length and density of the steel fibers. Load responses are presented and failure modes are discussed. Change in the bond behavior and load carrying capacity with increasing bonded length is analyzed to determine the effective bond length.

Abstract: This paper bases on the principle of the stress hybrid element, using voronoi cell finite element method to analysis the interfacial debonding phenomenon of a particle reinforced composite materials, then it contrasts by the commercial finite element software MARC in the same conditions of numerical simulation. Research results show that: In the interfacial debonding, especially at the crack tip stress, Stress is the biggest. Particles and matrix interface delamination is the important cause of material damage, at the same time, it has a great impact on the service life of components.

Abstract: The random distribution packing models of particles in the binder of solid propellant were generated based on the Molecular Dynamics method. The generated packing models were then analyzed by finite element method combined with the analytical method. A cohesive interface model was incorporated to capture the debonding process taking place along particles binder interface. The results show that the FEM analyses with cohesive interface can predict the complex heterogeneous stress and strain fields and the progress of debonding of particles from binder. Particles interaction significantly influences the interfacial damage evolution of propellant.

Abstract: This paper used Finite Element Method to investigate the influence of the circular face-core debonding dimension on the further debond propagation under the pure bending load in honeycomb structure. We also summarized the debonding rules and looked further into debonding area effect on the critical load for debond propagation. The conclusions are as follows: For a honeycomb panel, there exists a certain debonded radius . When the initial debonded radius is greater than , it will experience local buckling which takes the form of snap-through buckling. The debonding propagation is only discovered on the wide direction of the plate. The critical load for debonding propagation decreases with increased debond size.

Abstract: The paper presents a numerical investigation of mixed-mode crack induced failure of concrete beam strengthened with steel plate. Both the cracking of the concrete and concrete-steel interfacial debonding can be observed. There is a shear stress concentration at the pre-existing crack or debonding tips, which is the root cause of the debonding. The results indicate that debonding only initiates and propagates along the left interface to the steel plate because that the normal stress along the left interface is tensile which make considerable contribution to the debonding and the normal stress along the right interface is compressive.

Abstract: An energy-based analysis has been developed to evaluate interfacial adhesion between fiber and matrix in a single fiber composite over the years. However, the value of the energy-based parameter, e.g. an energy release rate, depends on a stress distribution predicted by a model employed. In the case of carbon fiber-reinforced plastics (CFRP), laser Raman spectroscopy (LRS) is significantly effective to validate the stress distribution predicted. The fragmentation tests with a model of carbon fiber-reinforced epoxy composite are performed, and LRS is used to detect a distribution of the fiber axial strain. An elasto-plastic shear-lag analysis methodology is employed, and a stress distribution is predicted under various approximations of s-s curve of the matrix resin and compared with the experimental results. Our recent energy-balance method, including an energy dissipation induced by plastic deformation around an interfacial debonding tip, is used to calculate an energy release rate to initiate an interfacial debonding (interfacial energy). An effect of the difference between the approximations on the value of the interfacial energy is discussed.

Abstract: The debonding of a rigid particle embedded in an infinite non-linear viscoelastic material is investigated in this paper. Under sphere-symmetric deformation, a non-linear equilibrium equation expressed by velocity of a particle in the viscoelastic matrix material is derived. The strain rate is obtained by solving non-linear equation in terms of iterative method. According to the energy criterion, the critical instant of the interfacial debongding is calculated. Numerical results show that the influence of non-linear viscosity on the interfacial debonding is significant.

Abstract: This research aims to investigate strain rate effect on transverse compressive strength of unidirectional fiber composites. Both glass/epoxy and graphite/epoxy composites were taken into account in this study. To demonstrate strain rate effect, composite brick specimens were fabricated and tested to failure in the transverse direction at strain rate ranges from 10-4/s to 500/s. For strain rate less than 1/s, the experiments were conducted by a hydraulic MTS machine. However, the higher strain rate tests were performed using a Split Hopkinson Pressure Bar (SHPB). Experimental observations reveal that the transverse compressive strengths increase corresponding to the increment of the strain rates. A semi-logarithmic function was employed to describe the rate sensitivity of the transverse compressive strength. SEM photographic on the failure surfaces depicts that for glass/epoxy composites, the failure mechanism is mainly due to the matrix shear failure, however, for the graphite/epoxy composites, it becomes the fiber and epoxy interfacial debonding which could dramatically reduce the transverse compressive strengths of the fiber composites.

Abstract: Voronoi cell finite element method (VCFEM) is introduced in this paper to describe the elastic-plastic-creep behavior of particle reinforced composites. The interfacial damage is simulated by partly debonding between Matrix and inclusion. A validation of the nonlinear behavior of the cell element has been carry out by comparing VCFEM results with those calculated by the general finite element package MARC and ABAQUS, and good agreements are found. A microstructure with five inclusions is taken as an example to describe the cyclic stress-strain behavior under different particulate orientation condition, and it shows the influence of the topological microstructure of inclusions. Thermomechanical fatigue properties are also investigated and the loops of stress-strain show the great differences of fatigue behavior between the in-phase case and out-of-case.