Ultrasonic Fatigue Testing of Metal Materials

Introduction

Generally it is known that with most structural metal materials the fatigue strength lowers until a load is applied 106 times, and from 107 times onward the fatigue limit is reached, at which no fatigue fracture will occur. However, it is also revealed that with highstrength metal materials that are hardened or surface treated, internal inclusions become an origin of a fatigue fracture and cause a fracture even at 108 to 109 cycles. On the other hand, recently, the functionality and endurance required for industrial products are becoming stringent, and according to this trend, metal materials forming industrial products must also meet rigorous requirements. Therefore, conventional testing with a maximum of 107 loading cycles is now insufficient, and a fatigue test exceeding 109 cycles has become required. However, such a fatigue test will take considerable time. For example, a test with 109 cycles at a frequency of 10 Hz theoretically requires about 3.2 years. The ultrasonic fatigue testing system used for this experiment enables testing at a frequency of 20 kHz, achieving a test with 109 cycles in about 14 hours. Therefore, this testing system is a very effective measurement system for fatigue tests exceeding 109 cycles. In this experiment, we used two kinds of metal specimens, SNCM439 and A6063, for testing according to WES 1112: 2017 (Ultrasonic fatigue testing method for metal materials) stipulated by the Japan Welding Engineering Society. The results are introduced in this article.

July 25, 2017 GMT