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A computationally efficient multiscale-multiphysics model aimed at predicting mechanical response of thermoplastic composites subjected to different levels of moisture was developed. The mathematical model of the coupled moisture-diffusion-mechanical-deformation phenomenon was stated at the microscale, based on the observed experimental data, and then upscaled using a mathematical homogenization approach. A two-way coupling between moisture diffusion and mechanical deformation was introduced by which diffusivity was enhanced by hydrostatic strain, whereas strength and stiffness were assumed to degrade because of moisture ingression, which also gives rise to swelling. The computational complexity of analyzing the two coupled physical processes at multiple scales was reduced via a model reduction scheme for multiple physical processes. The model was validated for 30% by weight filled glass fiber and carbon fiber reinforced thermoplastic composites. The moisture conditioning and uniaxial tension experiments were utilized to identify diffusion and mechanical properties at a fine scale. The identified properties were then used to validate the formulation in the three-point bending test. motor oil, brake fluid, gasoline, and battery acid) has often resulted in overdesign and thus limited their insertion in load bearing components because the overdesigned component may not yield any mass advantages. There are two main reasons for this state of affairs: (1) existence of multiple spatial scales and multiple coupled physical processes, such as thermal, mechanical, and moisture diffusion; and (2) costly environmental degradation experiments that require long time exposure of the test specimens to varied levels of humidity and temperature conditions. Among the various thermoplastic composites, short fiber thermoplastics have been increasingly used in the automotive industry. Their usage is intended to fill the gap in the mechanical properties between continuous-long fiber composites, primarily used as structural members, and unreinforced polymers, used as non-load bearing members. Glass and carbon short fibers are primarily used as reinforcements in polyamides (PA/nylon) or polyphthalamides. The main applications are in body parts, such as door panels, hoods, bonnets, and bumpers, and engine parts including cam covers, engine mounts, fuel tanks, fuel cells, and interior trims including molded seats. These materials are in demand because of their manufacturing ease, versatility, low cost, corrosion resistance, and superior mechanical, thermal, and electrical properties.Polyamides of semi-crystalline composition are known to absorb moisture because of their chemical structure. Experimental studies of PA-6, PA-66, and PA-46 polyamides report an equilibrium moisture content varying in the range from 1.2 to 2.5 wt.% of water at 50% relative humidity (RH) and 23 ı C temperatures and about 8-9 wt.% upon reaching saturation conditions [6][7][8][9]. The moisture is first absorbed in the microcracks and macrocracks/voids, if present, ...

SUMMARY A multiscale fatigue life prediction model is developed for heterogeneous materials. The proposed model combines a two‐scale asymptotic homogenization approach in time with a ‘block cycle jump’ technique into a unified temporal multiscale framework that can be effectively utilized for arbitrary material architectures and constitutive equations of microphases. The unified temporal multiscale approach in combination with a spatial multiscale approach based on the reduced order homogenization is characterized for high temperature ceramic matrix composites. Copyright © 2012 John Wiley & Sons, Ltd.

Noise in an acoustic array can be defined as any unwanted signal, and understanding how noise interacts with a structural system is paramount for optimal design. For example, in an underwater vehicle we may want to understand how structural vibrations radiate through a surrounding fluid; or an engineer may want to evaluate the level of sound inside a car resulting from the turbulent boundary layer (TBL) induced by a moving vehicle. This talk will discuss a means of modeling noise at a point of interest (e.g., at a sensor location) stemming from a known source by utilizing a power transfer function between the source and the point of interest, a generalization of the work presented in [1]. The power transfer function can be readily computed from the acoustic response to an incident wave field, requiring virtually no additional computation. The acoustic solution may be determined via analytic frequency domain approaches or through a finite element analysis, enabling the noise solution to be a fast post processing exercise. This method is demonstrated by modeling the effects of a TBL pressure and noise induced by structural vibrations on a sensor array embedded in an elastic, multi-layer solid. Additionally, uncertainties in the noise model can be easily quantified through Monte Carlo techniques due to the fast evaluation of the noise spectrum. Ko, S.H. and Schloemer, H.H. “Flow noise reduction techniques for a planar array of hydrophones,” J. Acoust. Soc. Am. 92, 3409 (1992).

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