A new model for the energy release rate of fibre/matrix interfacial fracture

On the basis of the well-known shear-lag analysis of fibre/matrix interface stresses and the assumption of identical axial strains in the fibre and matrix, a new model for predicting the energy release rate of interfacial fracture of the fibre pull-out test model is attempted. The expressions for stresses in the fibre, matrix and interface are derived. The formula for interfacial debonding energy release rate is given. Numerical calculations are conducted and the results obtained are compared with those of the existing models.

Theermal Stress and Fracture in Transparent Optical Materials due to Laser Energy-Absorption by a Defect

利用热弹性理论分析了在光学材料中由于缺陷吸收激光能量引起的温度和热应力分布,并且针对一个简单的裂纹模型分析了热应力产生的应力强度因子,给出了一些主要参数对于应力强度因子的影响的规律。

Energy Dissipation In Fracture Of Bulk Metallic Glasses Via Inherent Competition Between Local Softening And Quasi-Cleavage

Compression, tension and high-velocity plate impact experiments were performed on a typical tough Zr41.2Ti13.8Cu10Ni12.5Be22.5 (Vit 1) bulk metallic glass (BMG) over a wide range of strain rates from similar to 10(-4) to 10(6) s(-1). Surprisingly, fine dimples and periodic corrugations on a nanoscale were also observed on dynamic mode I fracture surfaces of this tough Vit 1. Taking a broad overview of the fracture patterning of specimens, we proposed a criterion to assess whether the fracture of BMGs is essentially brittle or plastic. If the curvature radius of the crack tip is greater than the critical wavelength of meniscus instability [F. Spaepen, Acta Metall. 23 615 (1975); A.S. Argon and M. Salama, Mater. Sci. Eng. 23 219 (1976)], microscale vein patterns and nanoscale dimples appear on crack surfaces. However, in the opposite case, the local quasi-cleavage/separation through local atomic clusters with local softening in the background ahead of the crack tip dominates, producing nanoscale periodic corrugations. At the atomic cluster level, energy dissipation in fracture of BMGs is, therefore, determined by two competing elementary processes, viz. conventional shear transformation zones (STZs) and envisioned tension transformation zones (TTZs) ahead of the crack tip. Finally, the mechanism for the formation of nanoscale periodic corrugation is quantitatively discussed by applying the present energy dissipation mechanism.

Additional response: Additional discussion of “Mixed mode ductile fracture using the strain energy density criterion”

boundary-layer flows, the skin friction and wall heat-transfer are higher and the

Response: Discussion of “Mixed Mode ductile fracture using the strain energy density criterion,” by E.E. Gdoutos

thermal conduction, and acoustic wave propagation are included. This

Application of the strain energy density criterion to ductile fracture

The strain energy density criterion due to Sih is used to predict fracture loads of two thin plates subjected to large elastic-plastic deformation. The prediction is achieved with a finite element analysis which is based on Hill's variational principle for incremental deformations capable of solving gross yielding problems involving arbitrary amounts of deformation. The computed results are in excellent agreement with those obtained in Sih's earlier analysis and with an experimental observation.

Fracture and energy partitioning in uncooked and cooked noodles

Humans perform fascinating science experiments at home on a daily basis when they undertake the modification of natural and naturally-derived materials by a cooking process prior to consumption. The material properties of such foods are of interest to food scientists (texture is often fundamental to food acceptability), oral biologists (foods modulate feeding behavior), anthropologists (cooking is probably as old as the genus Homo and distinguishes us from all other creatures) and dentists (foods interact with tooth and tooth replacement materials). Materials scientists may be interested in the drastic changes in food properties observed over relatively short cooking times. In the current study, the mechanical properties of one of the most common (and oldest at 4,000+ years) foods on earth, the noodle, were examined as a function of cooking time. Two types of noodles were studied, each made from natural materials (wheat flour, salt, alkali and water) by kneading dough and passing them through a pasta-making machine. These were boiled for between 2-14 min and tested at regular intervals from raw to an overcooked state. Cyclic tensile tests at small strain levels were used to examine energy dissipation characteristics. Energy dissipation was >50% per cycle in uncooked noodles, but decreased by an order of magnitude with cooking. Fractional dissipation values remained approximately constant at cooking times greater than 7 min. Overall, a greater effect of cooking was on viscoplastic dissipation characteristics rather than on fracture resistance. The results of the current study plot the evolution of a viscoplastic mixture into an essentially elastic material in the space of 7 minutes and have broad implications for understanding what cooking does to food materials. In particular, they suggest that textural assessment by consumers of the optimally cooked state of food has a definite physical definition. © 2007 Materials Research Society.

Interface energy and its influence on interface fracture between metal and ceramic thin films in nanoscale

A theoretical model about the size-dependent interface energy between two thin films with different materials is developed by considering the chemical bonding contribution based on the thermodynamic expressions and the structure strain contribution based on the mechanical characteristics. The interface energy decreases with reducing thickness of thin films, and is determined by such available thermodynamic and mechanical parameters as the melting entropy, the melting enthalpy, the shear modulus of two materials, etc. The predicted interface energies of some metal/MgO and metal/Al2O3 interfaces based on the model are consistent with the results based on the molecular mechanics calculation. Furthermore, the interface fracture properties of Ag/MgO and Ni/Al2O3 based on the atomistic simulation are further compared with each other. The fracture strength and the toughness of the interface with the smaller structure interface energy are both found to be lower. The intrinsic relations among the interface energy, the interface strength, and the fracture toughness are discussed by introducing the related interface potential and the interface stress. The microscopic interface fracture toughness is found to equal the structure interface energy in nanoscale, and the microscopic fracture strength is proportional to the fracture toughness. (C) 2010 American Institute of Physics. [doi:10.1063/1.3501090]

Nano-size Effect of Interface Energy and Its Effect on Interface Fracture

An analytical model about size-dependent interface energy of metal/ceramic interfaces in nanoscale is developed by introducing both the chemical energy and the structure stain energy contributions. The dependence of interface energy on the interface thickness is determined by the melting enthalpy, the molar volume, and the shear modulus of two materials composing the interfaces, etc. The analytic prediction of the interface energy and the atomic scale simulation of the interface fracture strength are compared with each other for Ag/MgO and Ni/Al2O3 interfaces, the fracture strength of the interface with the lower chemical interface energy is found to be larger. The potential of Ag/MgO interface related to the interface energy is calculated, and the interface stress and the interface fracture strength are estimated further. The effect of the interface energy on the interface strength and the behind mechanism are discussed.

Fracture surface, impact energy and hardness of Ni-free high-Mn steels

Two manganese steels were investigated: Fe-19.7%Mn (VM339A) and Fe-19.7%Mn stabilized with 0.056%C, 0.19%Ti and 0.083%Al (VM339B). The toughness of VM339A was higher than VM339B, but VM339B had higher hardness. Tempering does not affect the toughness of the alloys. SEM images of the fracture surface for both the alloys revealed ductile fractures. A further alloy with a lower manganese content, Fe-8.46%Mn-0.24%Nb-0.038%C, and thus even lower cost than the conventional 3.5Ni cryogenic steel, was tested for its impact toughness after heat treatment at 600°C, giving promising results.