The temperature variation in a cyclically loaded orthotropic composite is proportional to a linear combination of the changes in the normal stresses in the directions of material symmetry. An effective method is presented here to determine the individual stresses from measured thermoelastic data in a region adjacent to an arbitrarily shaped fraction-free boundary of loaded orthotropic composites. The method, which is based on equilibrium and compatibility, uses complex-variable formulations involving conformal mappings, analytic continuation and numerical techniques.

https://link.springer.com/content/pdf/10.1007/BF02319666.pdf

Thermoelastic stress analysis of orthotropic composites

Thermoelastic determination of stress intensity factors in orthotropic composites using the J-integral

In this paper, photoelastic experimental hybrid methods using the external traction free boundary condition and that using the relative equation of two stress functions in contact problems are developed. The validities of these two methods are confirmed through experiments and discussions. Hertz’s contact theory and the two photoelastic experimental hybrid methods explained are applied to the analysis of the contact stress of an O-ring under 10% or 20% squeeze rate. The photoelastic experimental hybrid method using the relative equation of two stress functions in contact problems was found to be more effective. When the squeeze rates of an O-ring were 10% or 20%, the maximum of absolute σx was greater than the maximum of absolute σy, but was almost equal. Maximums of absolute τxy were 1/8 of absolute σx and 1/5 of absolute σx when the squeeze rates of the O-ring were 10% and 20%, respectively.

Contact stress of O-ring under uniform squeeze rate by photoelastic experimental hybrid method †

A strain gage hybrid method is described for determining individual stresses on the boundary and in the neighborhood of cutouts in orthotropic composites. Results agree with independent measurements and finite element analysis. Few measured strain data are needed, and the measured strains originate away from the hole. Ability to determine the stresses on the edge of a cutout from nonboundary measurements recognizes the difficulties in obtaining reliable measurements very near an edge while circumventing the challenge of attempting to bond gages to the transverse curved surface of a small hole or notch. The method also alleviates the problem of not knowing a priori where the most serious stress will occur on the geometric boundary and, hence, where to locate strain gages.

Hybrid Stress Analysis of Perforated Composites Using Strain Gages

A hybrid experimental-numerical method is presented for evaluating the stresses around holes or notches in orthotropic composites. Moire-measured displacements and hybrid finite elements are employed. The geometric discontinuity of interest is surrounded by a hybrid element, which is a subregion within the physical structure. Measured displacements provide input information at nodal locations on the external boundary of the hybrid element. Little experimental data are needed, and the approach is accurate and effective. The method is demonstrated for a uniaxially loaded orthotropic laminate containing a central circular hole.

Hybrid moiré-numerical stress analysis around cutouts in loaded composites

Ability to determine the individual stresses photoelastically in orthotropic composites from isochromatic data, but without employing isoclinics or isopachics, is developed and demonstrated. This new capability is achieved by combining isochromatic information, complex stress functions and numerical nonlinear least-squares concepts into a new and effective hybrid method for stress analyzing composite materials. Unlike previous methods of photo-orthotropic-elasticity, the present technique simultaneously smoothes the recorded isochromatic data, provides reliable boundary information, and separates the isochromatics into individual stress components throughout the area of interest. The method is illustrated by evaluating the three individual stresses throughout a region adjacent to a hole in a uniaxially loaded orthotropic composite plate from the measured isochromatics.

J. S. Hawong

Papers

A Hybrid Method to Determine Individual Stresses in Orthotropic Composites Using Only Measured Isochromatic Data