Test analysis, micromechanical

Microcomposite tests including fiber pull-out tests are aimed at generating useful information regarding the interface quality in absolute terms, or at least in comparative terms between different composite systems. In this regard, theoretical models should provide a systematic means for data reduction to determine the relevant properties with reasonable accuracy from the experimental results. The data reduction scheme must not rely on the trial and error method. Although there are several methods of micromechanical analysis available, little attempt in the past has been put into providing such a means in a unified format. A systematic procedure is presented here to generate the fiber pull-out parameters and ultimately the relevant fiber-matrix interface properties. 

Wells J.K. and Beaumont P.W.R. (1982). Construction and use of toughness maps in a fracture analysis of the micromechanisms of composite failure. In Composite Materials Testing and Design. ASTM STP 787 (I.M. Daniel ed.), ASTM, Philadelphia, PA, pp, 147-162. 

Bannister, D.J., Andrews, M.C., Cervenka, A.J. and Young, R.J. (1995). Analysis of the single fiber pullout test by means of Raman spectroscopy. Part 11. Micromechanics of deformation for an aramid/ epoxy system. Composites Sci. Technol. 53, 411—421. 

Bohse, J., Krietsch, T., Chen, J., Brunner, A.J., (2000) Acoustic Emission Analysis and Micromechanical Interpretation of Mode I Fracture Toughness Tests on Composite Materials , Proceedings ESIS Conference on Fracture of Polymers, Composites and Adhesives, ESIS Publication 27, pp. 15-26, Elsevier, Oxford. 

As shown above, the ZrO/Ni composites examined by disk-bend testing are found to deform in a nonlinear manner, so that composition-dependent fracture strengths cannot be obtained directly from the stress-strain diagram in Fig. 3. Under the circumstances, we now make a micromechanical analysis to estimate actual stresses to be developed by plastic deformation of the ductile constituent on the basis of an established "mean-field" model [12]. In the following, the macrostress a) is related to the microstresses and (o) such... 

Through disk-bend testing on a series of ZrOj/Ni composite specimens fabricated by powder processing, we have examined the fracture behavior of ceramic/metal composites under an equibiaxial plane-stress loading, and derived, by making a micromechanical analysis of elastoplastic stress states, a brittle phase-controlled fracture criterion of the form, ( )max const., in terms of the equivalent normal stress a. This criterion is conceptually simple and quite useful particularly for our micromechanics-based approach to the FGM architecture. 

The single edge specimens were loaded under three-point bending at cyclic frequency of 10 Hz, stress ratio of 0.1. The FCGR tests were carried out in the laboratory air at the temperature of 20 °C and 700 °C. Several control tests of the composites were performed at the temperature of 800 °C. Optical and scanning electronic microscopy was used for analysis of microstructure and fracture micromechanisms of the materials. 

Kinematics analysis is a very important step to relate the micromechanics result with the macroscopic constitutive behavior. The reason is that the material parameters involved in the subphases and RVE need to be determined through macroscopic testing. For example, a... 

Miller AK, Adams DF (1978) Inelastic micromechanical analysis of graphite/epoxy composites subjected to hygrothramal cycling. In Vinson JR (ed) Advanced composite materials-environ-mental effects, ASTM STP 658, American Society of Testing and Materials, pp 121-142 Neumaim S, Marom G (1987) Prediction of moisture diffusion parameters in composite materials under stress. J Compos Mater 21(l) 68-80... 

After the tests, the fracture surfaces of the broken specimens were examined using light microscopy (Leica DMR) and scanning electron microscopy (Hitachi S-3400N) to analyze the extension of the stress-whitened region due to plastic deformation as well as the micromechanisms of failure. For scanning electron microscopy analysis, the samples were Au-Pd sputter coated. 

Verpoest et al. [81] presented a micromechanical analysis to show that for increasing applied strains, the fiber aspect ratio can reach values which are lower than those predicted by Kelly s shear-lag analysis. They also proposed that the single-fiber fragmentation test could be used to estimate the different components of the interface shear strength, that is, the bond strength, the friction strength and the matrix yield strength. 

The design and analysis of composite structures relies on experimental data. Testing of composites serves a variety of purposes such as the characterization of constituent materials i.e. the fiber, matrix and fiber/matrix interface, verification of the micromechanics analysis including the effects of curing stresses, temperature and moisture, as well as life prediction through accelerated testing[l]. 

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