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Technical Paper

A New Measurement of Aluminum Alloy Edge Stretching Limit Based on Digital Image Correlation Method

In Aluminum Alloy, AA, sheet metal forming, the through thickness cracking at the edge of cut out is one of the major fracture modes. In order to prevent the edge cracking in production forming process, practical edge stretch limit criteria are needed for virtual forming prediction and early stamping trial evaluations. This paper proposes new methods for determining the edge stretching limit of the sheet coupons, with and without pre-stretching, based on the Digital Image Correlation (DIC) technique. A numbers of sets of notch-shaped smaller coupons with three different pre-stretching conditions (near 5%, 10% and fractured) are cut from the prestretched large specimens. Then the notch-shaped smaller coupons are stretched by uniaxial tension up to through edge cracking observed. A dual-camera 3D-DIC system is utilized to measure both coupon face strain and thickness strain in the notch area at the same time.
Technical Paper

The Selection of Window in Spatial Phase Shift ESPI

Shearography is a laser based optical method that is similar to holographic interferometry and ESPI. It is a full-field, non-contacting and non-destructive measurement method for the surface deformation. It overcomes some of the disadvantages of holography; it does not need a reference beam, so that it obtains vibration isolation and simplifies the setup. These advantages grant shearography the ability to be a practical measurement tool and it has already gotten many industrial acceptances for non-destructive testing The embedment of the phase shift technique improves dramatically the measuring sensitivity and accuracy of the shearography. It uses the piezoelectric as the carrier to generate a known phase gap and takes multiple images with the phase before and after the sample is loaded, so that the phase map is calculated. And for each pixel the phase is accurate. However, the disadvantage of the phase shift technique is the time consumption.
Journal Article

Full Field Strain Measurement of Punch-stretch Tests Using Digital Image Correlation

Punch-stretch tests were conducted on Advanced High Strength Steel (AHSS) specimens. A special stretching mechanism with two embedded high resolution digital cameras had been designed and used in punch-stretch tests. The deforming processes were recorded by the cameras and the full-field strain distribution for each specimen was evaluated using Digital Image Correlation (DIC) technique, a full-field, non-contact, high accuracy optical and computational technique for contour, displacement and strain measurement. Data of Strain path, necking and other strain behavior were extracted using DIC. Different data analysis methods were tried to achieve useful information for predicting the failure. The data set could be used for researches on the effect of the strain path on the forming limit.
Journal Article

Scuffing Resistance of Surface Treated 8625 Alloy Steels

Scuffing is a common source of failure for many mechanical components in automobiles. 8625 alloy steel is commonly used in camshafts, gears, piston pins, shafts, and splines. The purpose of the research is to study the scuffing resistance of non-treated, carburized, nitrocarburized, and carbonitrided 8625 alloy steels. The scuffing resistance of the 8625 alloy steels was determined through pin-on-disk tests. The hardness and microstructure of the disks were analyzed using electron microscopy to determine wear mechanisms for each surface treated steel. The wear mechanisms were then related to the scuff resistance of the various materials.
Technical Paper

NDT of Weld Joints Using Shearographic Interferometry and Dynamic Exciation

Weld Joints are widely used in automotive and aerospace industry. The main issue in the weld joints is the quality inspection to detect the disconnection in the welded area. In this paper, Shearographic technique with dynamic excitation is introduced to test the weld joints. In the experiments, the coupons are of 4 very thin layers of metal sheets welded together. The goal is to find out if there are any disconnections between the layers. They are clamped and then excited by a PZT actuator from behind. A real time digital Shearographic system with a self-refreshed reference image technology has been developed to display the measuring result, i.e. shearogram. A big range of driving frequencies is scanned to find the proper frequency and amplitude that can help to identify the disconnections. The results show that when the driving frequency reaches the resonance frequency, there will be big amplitude and thus a fringe pattern becomes visible on the coupon surface.
Technical Paper

Measurement of Strain Distribution for Hole Expansion with Digital Image Correlation (DIC) System

Advanced high strength steels (AHSS) are increasingly used in automotive industry. A major issue for AHSS stamping is edge cracking. This failure mode is difficult to predict by conventional forming limit curve (FLC). The material edge stretchability is mainly evaluated using the hole expansion test. In this study, digital Image Correlation (DIC) is applied for strain measurement. DIC is a non-contact, full field, high accuracy and direct measurement technique that provides more detailed information for the evolution of strains on the sheet surface. Tests were conducted for five AHSS and nine cases. This paper will explain in detail the DIC technique and its results.