AN APPLICATION OF COMPUTER IMAGE-PROCESSING AND FILMY REPLICA TECHNIQUE TO THE COPPER ELECTROPLATING METHOD OF STRESS ANALYSIS

• Published in: Experimental techniques (Westport, Conn.) Conn.), 1994-01, Vol.18 (1), p.33-36
• Main Authors: Sugiura, M., Seika, M.
• Format: Article
• Language: English
• ISSN: 0732-8818; 1747-1567
• DOI: 10.1111/j.1747-1567.1994.tb00806.x

Strain gages made of Cu plating foil have been devised for measuring the elastic surface stress of machine parts in operation. When Cu plating foil is attached on the surface of a specimen subjected to repeated loads, grown grains or slip-bands occur in the foil. These phenomena are based on the repeated maximum shearing stress acting on the specimen. Hence, the elastic surface stress of the specimen can be measured by observing grown grains or slip-bands. The slip-bands are based on fatigue of the grown grains and usually observed through an optical microscope at a magnification of 100 times. Calibration studies with rotating-bending tests are performed on round steel bars with Cu plating foil, and the relation between the stress amplitude for the appearance of slip-bands and the number of cycles is established. The density of slip-bands in a field of the microscope depends upon the amplitude of cyclic stress and the number of cycles. Hence, for an assigned number of cycles, the stress value in a specimen can be determined from the density of slip-bands in the foil attached to the position in question. The density of slip-bands in a micrograph has been evaluated by the ratio of the area of slip-bands to the whole area, and it has usually been measured manually. However, this procedure is troublesome, and the measured value is apt to involve a personal error. In the study, referring to the technique proposed by Kato, a new technique to measure the density of slip-bands automatically is developed, namely, a TV image of the slip-bands observed through a microscope is directly processed by an image-processing system using a personal computer and an accurate value of the density of slip-bands is measured quickly. In the case of measuring the local stresses in machine parts of large size with the Cu plating foil, the direct observation of slip-bands through an optical microscope is difficult. In this study, to facilitate a technique close to the direct microscopic observation of slip-bands in the foil attached to a large-sized specimen, the replica method using a plastic film of acetyl cellulose is applied to replicate the slip-bands in the attached foil. The density of the replicated slip-bands also is measured automatically by the image-processing system. Under an assigned number of cycles, the density of the replicated slip-bands at a certain stress amplitude is compared with that of the original slip-bands. Furthermore, the peak stresses in stepped round ba