Stress submodel

The stress submodel results in the stresses and strains in the composite. Stresses and strains are introduced by fiber tension, thermal expansion or contraction, and chemical changes. The effects of fiber tension, temperature and chemical changes may arise simultaneously however, the stresses and strains are analyzed separately. The sum of the stresses and strains caused by each of these factors is the actual stress and strain in the composite. 

The temperature, fiber tension, stresses, and strains vary only in the radial directions. An elasticity solution is employed to calculate the six components of the stresses and strains. The solution procedure follows the established techniques of elasticity solutions. A displacement field is assumed that satisfies the equilibrium equations and the compatibility conditions. The latter requires that at each interface the displacements and the normal stresses in adjacent 

The implementation of mandrel removal is of particular interest in winding model formulation. When the mandrel is removed, there is no radial stress jrr at the cylinder inner diameter (Eq. 13.18) 

This requirement is imposed by adding a radial stress at the cylinder inner diameter that is equal but opposite in magnitude to the contact stress between the mandrel and cylinder. The contact stress corresponds to the radial pressure at the interface at the time the mandrel is removed. 

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Solutions to these equations yield the temperature distribution inside the mandrel and inside the composite as a function of time. Degree of cure or crystallinity and matrix viscosity in the composite as a function of time are also determined. This model is the building block for the other submodels. Viscosity calculations are input to the fiber motion submodel. Temperature and cure calculations are input to the stress submodel. Temperature data are also input to the void submodel. 

The master model consist of five submodels a) Kinetic submodel or crystallization submodel b) Heat transfer submodel c) Pressure model d) Pulling force submodel e) Residual stress submodel. Figure 3 shows the generalized scheme of the pultrusion process. 

Stress/strain submodel Stresses within the composite that occur during winding, as a result of heating/cooling, or upon mandrel removal are evaluated in the stress/strain submodel. 

Stress-Strain Submodel Winding and Thermal Loads... 

The fiber motion submodel yields the fiber position during processing. In filament winding, the fiber position is affected by flow of the resin matrix material, expansion of the mandrel, and expansion of the composite. In the fiber motion submodel, only changes in fiber position caused by flow of the matrix are considered. Changes caused by thermal expansion of the mandrel and composite are included in the stress-strain submodel. 

In comparison with the PEFC, the HT-PEFC requires a description of the electrochemistry with modification to higher tolerance against carbon monoxide (CO) and a simpler approach to fluid flow because of the absence of liquid water. The CO tolerance requires special submodels that account for the reversible decrease in catalyst activity if the fuel is reformate gas. Compared with the SOFC, the HT-PEFC requires different electrochemical parameters because of the very different catalysts and operating temperatures and the use of H+ instead of 0 as charge carrier. Thermomechanical stress is less important because of the much more moderate operating temperature. 

A submodel is created of the worst-case solder joint (the one that shows the most stress or deformation in the global model). The files stored in step 2 are applied as load boundary c nditions on the nodes forming the submodel boundary at each temperature step. Temperature-dependent material properties should be used in both models. 

Stress results for the submodel structure and comparison with the analytical solution and the stress obtained from the coarse mesh... 

Further development, implementation, and interpretation of devices for in situ measurement of sediment erosion, especially in systems with heterogeneous (cohesive and noncohesive) bottom sediment properties (e.g., grain size distribution, dry bulk density porosity, organic carbon content) and development of submodels for predicting sediment resuspension as a function of more easily measured sediment properties and modeled bottom shear stress. 

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