Optimisation Method for Determination of Crack Tip Position Based on Gauss-Newton Iterative Technique

In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life prediction.This paper proposes a Gauss-Newton iteration method for solving the crack tip position.The conventional linear fitting method provides an iterative initial solution for this method,and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix.A noise-added artificial displacement field is used to verify the feasibility of the method,which shows that all parameters can be solved with satisfactory results.The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result,and the relative error between the two is only−0.621%;The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip,and the maximum relative error with the test plastic zone area is−11.29%.The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05%.The crack tip coordinates,stress intensity factors,and plastic zone contour changes in the loading and unloading phases are explored.The results show that the crack tip change during the loading process is faster than the change during the unloading process;the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process;under the same load,the theoretical plastic zone during the unloading process is higher than that during the loading process.

A Method to Measure Eye-Hand Coordination for Extracting Skilled Elements-Simultaneous Measurement of Eye-Gaze and Hand Location-

The purpose of this study was to construct bases for exploring the process of skill acquisition from the viewpoint of eye-hand coordination. The information obtained from eye-gaze is closely related to physical movements in any activity. It is important to establish a method to measure eye-hand coordination for extracting skilled elements and understanding the skill acquisition process. Using a system which consists of an eye mark recorder and a three-dimensional location measurement device, a method for measuring eye-hand coordination was proposed on the basis of the simultaneous measurement of eye-gaze and brush tip locations. After describing the measurement algorithm, the eye-hand coordination during calligraphy was exemplified. More concretely, using such a system, an attempt was made to show that the relationship between the line of eye-gaze and the brush tip stroke was different between a novice and an expert. In such a way, we suggested that the proposed method is promising for exploring the process of skill acquisition.