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WOSInternational audiencePolymer matrix composites, and especially short glass fibre reinforced polyamides, are widely used in the automotive industry. Their application on structural components requires a confident mechanical design taking into account the sensitivity of the mechanical response to both temperature T and relative humidity H. In this paper, the constitutive model already developed by the authors (Launay et al., 2011) is applied to describe the non-linear time-dependent behaviour of a PA66-GF35 under various hygrothermal conditions. The extensive experimental database involves testing conditions under and above the glass transition temperature Tg. An equivalence principle between temperature and relative humidity is applied and validated, since the non-linear mechanical response is shown to depend only on the temperature gap T-Tg(H)

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In this paper, a method for the construction of a cracked beam finite element is presented. The additional flexibility due to the cracks is identified from three-dimensional finite element calculations taking into account the unilateral contact conditions between the crack lips. Based on this flexibility, which is distributed over the entire length of the element, a cracked beam finite element stiffness matrix is deduced. Considerable gain in computing efforts is reached compared to the nodal representation of the cracked section when dealing with the numerical integration of differential equations in structural dynamics. The stability analysis of a cracked shaft is carried out using the Floquet theory.

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Article Number: 082101International audienceA lifing technique for predicting fretting fatigue on highly loaded blade-disk attachments has been developed and calibrated. The approach combines extensive testing on nickel and titanium based alloys using a specially devised multiaxial fretting test machine and an analytical lifing procedure, based on finite element contact calculations and multiaxial shakedown fatigue models. In order to reproduce realistic operational conditions and standardize testing conditions, a special fretting fatigue testing machine with high temperature testing capabilities was developed. The machine was employed to perform systematic testing under prescribed load and displacement conditions at representative temperatures. Making use of FEA, the rig test results were calculated to identify relevant parameters such as friction coefficient, slip conditions, and machine compliance. The computation procedure involves the calculation of several major loading cycles until a stabilized response of the structure is achieved. The material response is assumed to be elastoplastic, and a nonlinear friction law (space and time) was applied. From the computed mechanical variables, several life prediction models are benchmarked to establish their capabilities to predict fretting fatigue life. Finally, a most promising life estimation procedure was applied to predict life in a real compressor blade-disk attachment. Predicted failure location and number of cycles to failure are compared against engine test results. The experimental-analytical approach has the potential to predict fretting fatigue risk during the design phase on highly loaded joints, as well as estimating the preventive overhaul intervals for parts already in service