SUMMER 2020

14 THE DISTRIBUTOR’S

14 THE DISTRIBUTOR’S LINK Rob LaPointe AIM TESTING LABORATORY Rob LaPointe is a noted authority in materials and fastener technology. With extensive experience in the management and science of materials testing laboratories combined with master’s degrees in physics and education, he excels at bringing solutions to the client. Working specifically in the fastener testing industry, he has developed expertise in mechanical, nondestructive, metallurgical and chemical testing. With a background of 20 years in physics education, Rob is effective at communicating complex ideas in a simple and understandable manner, communicating well with clients enabling them to make informed decisions about their products and business. AIM is located at 1920 Cordell Court #101, El Cajon, CA, 92020. Tel: 909-254-1278, email: sales@aimtestlab.com or online at www.aimtestlab.com FASTENER SCIENCE: CHARPY IMPACT TESTING Charpy impact testing is the most fundamental test to determine the fracture toughness of metal. It is both simultaneously a brutish and eloquent test, striking a metal bar with a big hammer so that it breaks into two pieces. On the eloquent side, the test makes use of a simple mechanism that uses the force of gravity on a falling pendulum and fundamental physics to determine the amount of energy consumed by the fracturing specimen. Charpy impact testing, also known as Charpy V-notch (CVN) was first developed by S.B. Russell in 1896, although Russell’s initial tests were done on bars of metal without a notch. In 1901, Georges Charpy introduced the notched specimen (Figure 1) and test standardization with both the specimen and the impact tester (Figure 2). Charpy’s contributions to standardize both the specimen and testing apparatus enabled the test results to characterize materials and tempering techniques and to compare the fracture toughness among them. Charpy’s contributions to the science of the test were so significant, the test was named after him. FIGURE 1 CHARPY V-NOTCH (CVN) SPECIMEN TECHNICAL ARTICLE FIGURE 2 CHARPY IMPACT TESTING MACHINE The testing specifications that govern test specimens and testing machines are specified in both ASTM E23 and ISO 148-1. Both specifications provide specimen geometry, testing machine tolerances and calibration parameters. The standard CVN bar is 10 x 10 mm square and 55 mm long (Figure 1). The V-notch is 45 ° and has a root radius of 0.25 mm. The geometry of the specimen has a tight tolerance so that the resulting energy measurement is comparable between the specimens in a test group as well as from one test to another on the same material and temper. A test group consists of three samples tested together. The purpose of the V-notch is to both direct the fracture to occur in the middle of the specimen in addition to providing a standardized stress-riser and fracture area. CONTINUED ON PAGE 104