The Incremental Strain, Average Stress, Power Series, and Integral methods are examined as procedures for determining non-uniform residual stress fields using strain relaxation data from the hole drilling method. Some theoretical shortcomings in the Incremental Strain and Average Stress methods are described. It is shown that these two traditional methods are in fact approximations of the Integral Method. Theoretical estimates of the errors involved are presented for various stress fields. Also, some simple transformations of stress and strain variables are introduced so as to decouple the stress/strain equations and simplify the numerical solution.

The Integral Method for calculating non-uniform residual stress fields using strain relaxation data from the incremental hole-drilling method is examined in detail. Finite element calculations are described which evaluate the calibration coefficients required for practical applications of the method. These calibration data are tabulated for a range of hole sizes and depths. It is found that the hole drilling method is not well adapted to measuring stresses remote from the surface, and a theoretical depth limit for stress measurements of 0.5 of the mean radius of the strain gauge rosette, rm, is identified. A practical depth limit is in the range 0.3–0.4 rm.

For most of the destructive methods used for measuring residual stresses, the relationship between the measured deformations and the residual stresses are in the form of an integral equation, typically a Volterra equation of the first kind.Such equations require an inverse method to evaluate the residual stress solution.This paper demonstrates the mathematical commonality of physically different measurement types, and proposes a generic residual stress solution approach. The unit pulse solution method that is presented is conceptually straightforward and has direct physical interpretations. It uses the same basis functions as the HoleDrilling integral method, and also permits enforcement of equilibrium constraints.In addition, Tikhonov regularization is shown to be an effective way to reduce the influences of measurement noise. The method is successfully demonstrated using data from Slitting (crack compliance) measurements, and excellent correspondence with independently determined residual stresses is achieved. January 20052

The use of finite element calculations is assessed as a means of analysis of the strain relaxation data from a measurement of residual stress by a material removal method. This application is important because it allows a greater flexibility of choice for specimen shape, materials, and experimental procedure than would be possible if only analytic or experimental calibrations are used. Three possible applications are described using the hole-drilling method as an example, and comparisons of calculated results and experimental measurements are presented.

A mathematical model is developed to simulate the drying of hygroscopic porous media and, in particular, of wood. Drying rate experiments were performed using wood specimens and a nonhygroscopic porous ceramic solid and were simulated using the appropriate version of the drying model. Calculated model predictions are in very satisfactory agreement with experimental results. An examination of the relative impacts on drying of the transport mechanisms that comprise the model leads to meaningful interpretations of observed drying behavior. Controlling rate factors can be identified and different types of drying behavior specific to a given material or drying condition can be explained and understood through model simulation studies. Such capability can provide important guidance for drying process design and control. M. A. Stanish, G. S. Schajer, Ferhan KayihanWeyerhaeuser Technology Center Tacoma, Washington 98477 SCOPEThe drying of moist porous solids is a complicated process involving simultaneous, coupled heat and mass transfer phenomena. Accordingly, drying behavior can be influenced by a rather large variety of independent factors, including, for example, ambient conditions of temperature, air velocity, and relative humidity, and solid properties such as density, permeability, and hygroscopicity. Extensive characterization of drying behavior using a strictly experimental approach constitutes a formidable challenge due to the excessively large number of variables that must be considered. The task becomes more manageable, however, with the help of a reliably realistic mathematical model of the drying phenomenon. Our objective is to develop such a tool to simulate drying behavior and therefore allow us to extend the results of experimental drying investigations. In this way, the impact of the many variables on drying behavior can be examined and interpreted without having to resort to an extensive program of experimental testing.The approach taken here represents advancement of drying modeling and theory on several fronts. The mathematical description of the drying process is derived and maintained for the most general case; a comprehensive set of fundamental heat-and mass-transfer mechanisms is coupled with thermodynamic phase equilibrium expressions in a way that accommodates either hygroscopic or nonhygroscopic materials. Heat transfer by both conduction and convection is included together with mass transfer by gaseous diffusion and bulk flow of gas and liquid through the void space and by bound-water diffusion through the solid matrix. Bound-water migration is expressed in terms of the diffusion of sorbed water driven by the gradient in the chemical potential of the bound molecules. While this concept of bound-water diffusion was previously suggested by Siau (1983) and others (Kawai et al., 1978), in this development a new, uniquely explicit expression for bound-water flux is derived in terms of temperature and vapor pressure gradients. Combination of all of these transport mechanisms in a single generalized ...