One of the important factors affecting the accuracy of stress values obtained from holedrilling method is the calibration coefficient. A three-dimensional model was established to determine the calibration coefficients for integral method. The constraint conditions and loading conditions during hole-drilling can be simulated more realistically with this method. With this new model, coefficients ā i,j and b i,j could be determined within one computation procedure. The relationship between calibration coefficients and plate thickness was investigated over a wide range of plate thickness. It has been found that the calibration coefficients determined in this work may vary with thickness of plates and the thickness range for thin plates was thus well defined. The calibration coefficients can thus be extended to measure the residual stresses of either thin or thick plates. Comparison of calibration coefficients with those determined by other studies was also conducted.

On the Improvement of Calibration Coefficients for Hole-Drilling Integral Method: Part I—Analysis of Calibration Coefficients Obtained by a 3-D FEM Model

Due to the moisture and temperature gradients developed during hot pressing of medium density fibreboard (MDF), residual stresses occur within the board as it equilibrates to room conditions. It would be extremely useful to measure these residual stresses and to determine their effects on board properties such as moduli of elasticity and rupture in bending, internal bond strength and dimensional stability. In this article two methods, namely dissection and hole drilling, have been adapted to measure residual internal stress distributions in six different samples of industry produced MDF. The dissection method involves cutting several pieces of MDF perpendicular to the thickness direction at different depths. The residual stresses released by the dissection can be determined by measuring the curvatures of cut pieces and knowing their elastic moduli. The hole drilling method, on the other hand, involves mounting three strain gauges on the surface of a piece of MDF and drilling a hole to release residual stresses in close proximity. The released stresses are manifested as strains in the forms of which can be measured in three directions on the surface of the board. A theoretical model for predicting residual stresses involving various parameters has been developed and an excellent agreement with the experimental results from both the dissection and hole drilling methods has been achieved. Linear moisture expansion coefficient appears to have the greatest influence on residual stress. When compared against each other, the residual stresses measured by the hole drilling method show some shortcomings towards the centre of the board. While all six of the MDF boards exhibited similar trends in their residual stress distributions, significant differences were identified in the magnitudes of residual stress measured. Finally, some preliminary results linking the residual stress with the thickness swell of the samples and their surface densities have been presented.

Determination of residual stresses in medium density fibreboard.

Demands placed on dissimilar metals joints have increased from various
viewpoints, such as, environmental concerns, energy saving, high performance, cost
saving and so on The aim of this research is to predict and optimize laser welding of
some economically important dissimilar materials in industry through applying a
Taguchi orthogonal array design as a DOE approach to design the experiments,
develop mathematical models and optimize the welding operation This was achieved
by controlling selected welding parameters; laser power, welding speed and focus
position, to relate the mechanical properties, weld bead geometry, principal residual
stress and unit operating cost to the selected input welding parameters The dissimilar
materials studied in this work are low carbon steel, 316 stainless steel, titanium G2,
different types of aluminium alloys such as (6082, 5251H22 and 1050H24) with
different thicknesses and different joint designs
For each dissimilar welded material, mathematical models were developed to
predict the required responses Moreover, the main effects and the interaction effects
of the process parameters on the responses were discussed and presented graphically
for all dissimilar materials and joint designs Furthermore, the developed models
were optimized by determining the best combinations of input process parameters in
order to produce an excellent weld quality

Feasibility and optimization of dissimilar laser welding components

The hole drilling method is widely used in measuring residual stress in surfaces. In this method, the inclination of holes is one of the sources of error. This paper presents a finite element analysis of the influence of inclined holes on the uniaxial residual stress field. The error in stress has been found to increase proportionally to the correct inclined angle of the hole. The correction equations by which one may easily obtain the residual stress, taking account of the inclined angle and direction, have been derived. The error of stress due to the inclined hole has been reduced to around 1% using the correction equations.

Influence of inclined holes in measurement of residual stress by the hole drilling method

Experimental investigation on residual stress distribution in an austenitic stainless steel weld overlay pipe after local ultrasonic impact treatment

In general industry, especially in the nuclear industry, welding overlay repair is an important repair method mainly used to rebuild piping systems suffering from intergranular stress-corrosion cracking (IGSCC).

M. C. C. Lin

Papers

Measurement of residual stress in the weld overlay piping components