Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.6, #5)
Bridging at the Nanometric Scale in 2.5D Cf–SiC Composites by Guillaume Boitier; Jean-Louis Chermant; Jean Vicens (pp. 279-287).
This short paper presents the matrix microcrack bridging at a nanometric scale which was evidenced during creep tests of 2.5D Cf–SiC composites. It also shows the importance of the investigations of mechanical behavior of composite materials at all the different scales: from the macroscopic down to the nanoscopic one.
Keywords: creep; microcrack bridging; nanoscale; 2.5D Cf-SiC; ceramic matrix composite
Optimum Design of Thick-Walled Multi-Layered CFRP Pipes to Reduce Process-Induced Residual Stresses by Hideki Sekine; Eui-Sup Shin (pp. 289-307).
Process-induced residual stresses may cause cracking in thick-walled multi-layered CFRP pipes during the curing of the pipes, significantly affecting the ultimate structural performance. Several factors influence the amount of the residual stresses, such as thermal and elastic properties of CFRP, and stacking sequences and dimensions of pipes. This paper deals with the optimum design of thick-walled multi-layered CFRP pipes by minimising the process-induced residual stresses under some constraints of structural stiffnesses. An analytic model based on quasi-static thermoelasticity is adopted for the calculation of the residual stresses in the multi-layered CFRP pipes. The numerical results of optimisation show that, in the case of cross-ply pipes, the residual stresses can be reduced to a certain level by controlling ply thicknesses. However, in real process conditions, the optimised pipes are susceptible to cracking because the transverse residual stress is still large in a strength-based sense. To further suppress the residual stresses, the effects of stacking sequence, wall thickness and axial pre-tension on the optimum solutions are carefully examined.
Keywords: multi-layered CFRP pipe; optimum design; cross-ply; process-induced residual stress; pre-tension
Molded Carbon–Carbon Composites Based on Microcomposite Technology by Alisa Buchman; Robert G. Bryant (pp. 309-326).
A one-step, cost-effective processing methodology based on compression molding of a mixture of graphite particles and short fibers, both coated with a soluble polyimide adhesive was developed. This technique shows a considerable potential in decreasing the complexity of the current carbon–carbon fabrication procedures. The new process eliminates additional infiltration and densification steps following the initial carbonization, which reduces the processing time from 5 weeks to 3–5 days and saves energy. The structure and properties of the new carbon–carbon composites were characterized using optical and electronic microscopy, thermal analysis, density and porosity measurements, and mechanical properties (hardness and flexural strength).The flexural strengths ranged from 20–45 MPa. The densities ranged from 1.9 to 2.2 g/cc (which is close to pure graphite) while the porosity was as low as 3%. The CTE was approximately ± 1 ppm/○C (R.T. to 550○C). The thermal stability of the carbonized and graphitized specimens when heated in flowing air up to 500○C and flowing nitrogen up to 1000○C showed no observable weight loss.There are numerous applications for these materials which include: optical mirrors, medical implants, thermal radiators and parts for rotating equipment, etc.A car piston was successfully molded using a mixture of polymer coated graphite powder, flakes and chopped fibers.
Keywords: carbon–carbon; microcomposites; polyimide resin; pyrolysis; graphite molding compounds
On the Method of Determination of Strain Energy Release Rate During Fatigue Delamination in Composite Materials by D. Dalmas; A. Laksimi (pp. 327-340).
In this paper, the problem of calculation of the energy release rate for a fatigue test on composite material has been investigated. The application of the Linear Elastic Failure Mechanics (LEFM) leads to the use of varation of the energy release rate (Δ G). As the energy release rate is a function of the load squared, the variation of G becomes either a function of variation of the load squared (Δ G = f(Δ(P2))) or a function of the square of the load variation (Δ G = f((Δ P)2)).In this paper, we determine, by different fatigue tests, which of the two theoretical results is the best to describe the experiments. These fatigue tests have been made on DCB test-specimen in mode I with different R ratios (R = Pmax / Pmin) and different maximum loads. The material was a unidirectionnal glass-epoxy.The results show that considering Δ G as a function of (Δ P)2 $$(Delta G = frac{1}{2}(P_{max } - P_{min } )^2 frac{{partial C}}{{partial A}} = frac{1}{2}(P_{max }^2 (1 - R)^2 frac{{partial C}}{{partial A}}$$ seems more appropriated to describe a cracking test in fatigue.
Keywords: fatigue; energy release rate; mode I delamination; R ratio; failure mechanics