Creep Behavior Of Composites Research Articles

High-temperature deformation of Al 2O 3/Y-TZP particulate composites

Al 2O 3/Y-TZP particulate composites with compositions of between 20 and 80 vol.% Y-TZP were produced by tapecasting, lamination, and sintering. The processing methods employed resulted in fine grain sizes with only small variations between the composites produced. The resulting particulate composites were tested in compression at a temperature of 1350 °C over strain rates from 10 −5 to 3.16×10 −4 s −1. Microstructural changes during testing were minor. Stress exponents were measured to the range from approximately two to three, which are consistent with published data on similar materials from tensile experiments. Models of composite creep behavior are compared to the experimental data over the full range of compositions studied. A constrained isostrain model is found to provide better predictive capabilities than either an unconstrained model, an isostress model, or a rheological model. Furthermore, the constrained isostrain model provides the most reasonable predictions for creep rates of 100% Al 2O 3 and 100% Y-TZP materials.

Oxide-fibre/Ni-based matrix composites—III: a creep model and analysis of experimental data

Recent results of creep and creep-rupture experiments with oxide-fibre/Ni-based-matrix composites at temperatures of 1100–1200 °C clearly showed a need to use adequate models of the creep behaviour of composites to enable their behaviour to be analysed appropriately. In the present paper, a new creep model for a composite with creeping matrix and initially continuous brittle elastic fibres is developed. The model accounts for fibre breakage in the transitional stage of creep and steady-state conditions are found by evaluating an average fibre length that cannot be divided into shorter segments. The model allows analysis of the dependence of composite creep rate on such composite microstructure parameters as statistics of the fibre strength, creep characteristics of the matrix, and the fibre/matrix interface strength. Comparison of calculated results with experimental behaviour shows the applicability of the model to computer simulation of the creep behaviour of heat-resistant composites as well as to optimising the composite microstructure. Combining the experimental data with results of calculations evaluates both present and future potentials of oxide-fibre/Ni-based-matrix composites. Composite specimens obtained and tested up to now show the possibility of their application as heat-resistant materials up to a temperature of 1150 °C. The maximum use temperature can be essentially enhanced provided a better fibre/matrix bonding has been achieved.

ＴｉＢ分散Ｔｉ基複合材料を用いたクリープ変形挙動

In order to estimate dependence of volume fraction of ceramic and metallic phase on composite's creep behavior, we fabricated Ti-TiB in situ composites whose volume fractions of TiB were 10, 24 and 40%. The steady-state creep rates of all composites were agreement with the estimation of continuum mechanic. Microstructure of Ti-40TiB, however is quite different from that of Ti-10TiB, because TiB whiskers are strongly connected each other in Ti-40TiB. This structure of Ti-40TiB seems to require the deformation off TiB to creep, and of creep behavior of composites with high volume fraction of reinforcements requires more extensive study.

The creep response of uni-directional fiber-reinforced ceramic composites: a theoretical study

Both the finite-element technique and the elastic-viscoelastic correspondence principle (in conjunction with the Hashin and Aboudi methods of calculating the effective elastic properties) methods have been used to calculate the effective creep properties of SCS6 (fiber)/SiC (matrix) composites and the results have been compared. In the finite-element technique, three different arrangements of fibers were used to study the effects of fiber arrangements on the creep properties of the composite. Effects of the fiber volume fraction on the creep behavior of composite were also studied. No significant difference was found in the longitudinal compliance, S 11 (i.e. the compliance along the fiber axis), calculated from the five models. But, it was found that the fiber arrangement plays an important role in the transverse compliance, S 22, and transverse shear compliance, S 44. For S 22, the correspondence principle method based on Aboudi method and the square array of fibers in the finite-element technique gave the upper and lower bounds, respectively. For S 44, the square array of fibers in the finite-element technique and the correspondence principle method based on Hashin (for low volume fraction of fiber)/Aboudi (for high volume fraction of fiber) method gave the upper and lower bounds, respectively. The effects of fiber arrangements on S 22 and S 44 are explained by the strain energy and the energy dissipation due to creep.

Effect of stressed pre-exposure on the creep strengthening of a 2009 Al-SiC w composite

Clearly the present approach of analyzing the steady state or minimum creep data on the basis on a threshold stress is not likely to produce an unambiguous interpretation of the steady state creep mechanism in aluminum alloy matrix composites. In the authors` opinion it is important to (a) establish the existence of a true steady state creep regime in tension over a large enough strain rate range (e.g. a typical creep rate range for experimental verification would be 10{sup {minus}9}--10{sup {minus}5} s{sup {minus}1}), (b) establish a criterion for the lack of a true steady state creep regime (in at least some composites), and (c) look for some other creep parameter to understand the differences in the creep behavior of composites and unreinforced matrices. In this paper the authors report the creep behavior of a 2009Al-SiC{sub w} composite (w denotes whisker). They note that no steady state creep regime was observed at higher creep rates. Specimens pre-exposed at a prior stress (and only in a critical range) show an unusual creep strengthening. This observation hints at the role of matrix composition on overall creep behavior of composites. The primary creep strain and anelastic strain values are reported to highlight the rolemore » of SiC{sub w} reinforcement on the overall dislocation activities during creep.« less

Creep Mechanisms in Niobium-Silicide Based In-Situ Composites

ABSTRACTThis paper will discuss the relationship between microstructure and creep behavior in hightemperature niobium-silicide based in-situ composites. The creep behavior of composites generated from binary Nb-Si alloys, and higher order alloys containing Mo, Hf and Ti additions, will be described. In-situ composites were tested in compression at temperatures up to 1200°C and stress levels in the range 70 to 280MPa. It was found that the Hf concentration can be increased to 7.5 with little increase in creep rate, over that for the binary Nb3Si-Nb composite, but at higher concentrations the creep rate is increased at stress levels higher than 21OMPa. At stresses less than 21OMPa the Ti concentration can be increased to 21 without a detrimental effect on creep performance, but at higher concentrations there is a substantial increase in the creep rate.

Creep of Cr 2Hf + Cr in situ intermetallic composites

Intermetallics are attractive for high temperature applications due to their high melting temperature and high temperature strength. One of the principal requirements for high temperature use is the creep strength. At present very little information on creep is available in intermetallics and it is even rare in the case of two phase intermetallic composites indicated above. In previous studies, the effects of microstructure and heat treatment on the mechanical behavior as a function of temperature, including flexure strength, ductility and fracture toughness of Cr{sub 2}Hf + Cr composites were investigated. The objective of the present study is to investigate the creep deformation characteristics of Cr{sub 2}Hf + cr composite. Creep data for one hypoeutectic microstructure and for the eutectic microstructure in this composite system were determined at 1,200 C and are compared with that of pure Cr. Estimates of composite creep behavior, made using known models, are also presented.

Creep Behavior of Fiber-Reinforced Polymeric Composites: A Review of the Technical Literature

This report provides a review of the technical literature related to the creep behavior of fiber reinforced polymer (FRP) composites. The review presented here was directed toward those papers that define the direction and line of thinking in the area of experimental techniques that may be candidates for the development of accelerated test methods to predict the long-term performance of FRP composite materials for highway structural applications. Linear and nonlinear viscoelastic theories as they relate to the modeling and prediction of the viscoelastic response of FRP materials under constant loads are included. Accelerated characterization techniques for the viscoelastic behavior of FRP composites including the use of elevated temperatures and frequency domain loading are reviewed. The effects of moisture and temperature on the creep behavior of composites are briefly considered. The interaction between creep behavior and fatigue behavior is also included in the discussion.

Creep behavior of unidirectional composites

The creep behavior of the continuous fiber reinforced unidirectional composites due to the viscoelasticity of the resin matrix is investigated assuming that the constituent matrix obeys the nonlinear creep law and the fiber is the linear elastic materials. Utilizing a quasi three-dimensional finite element method, the macroscopic creep behavior of the composites with regular fiber packing is obtained, giving the orthotropic creep law for the composites. Then, the creep of the composites with random fiber packing is estimated applying the random model proposed by Kondo and Saito in which the neat matrix cylinders are embedded in the regular array composites. The theoretical predictions for the creep behavior are compared with the experimental results.

Creep behavior of discontinuous SiCAl composites

A review of creep data of discontinuous SiCAl composites (whisker and particulate) shows that the creep behavior of these composites exhibits two main characteristics: (a) the stress dependence of the steady state (or minimum) creep rate, as described by the value of the stress exponent, is high and variable and (b) the temperature dependence of the steady state (or minimum) creep rate, which is measured by the creep activation energy, is much larger than that for self-diffusion in aluminum. These two characteristics are examined in the light of theoretical treatments describing the origin of high temperature strengthening in discontinuous metal matrix composites and dislocation models proposed for dispersion-strengthened alloys.