机电技术专业英语 教学课件 作者 徐起贺 张庆良pata b lesson two.pptVIP

* 机电技术专业英语 Lesson two Text Brinell Hardness Test Method Dr. J. A. Brinell invented the Brinell test in Sweden in 1900. The oldest of the hardness test methods in common use today, the Brinell test is frequently used to determinate the hardness of forgings and castings that have a grain structure too course for Rockwell or Vikers testing. Therefore, Brinell tests are frequently done on large parts. By varying the test force and ball size, nearly all metals can be tested using a Brinell test. Brinell values are considered test force independent as long as the ball size/test force relationship is the same. Standards Brinell test methods are defined in the following standards: ASTM E10 ISO 6506 Brinell and Rockwell Hardness Test Method Lesson two Brinell Test Method All Brinell tests use a carbide ball (Figure B.1). The test procedure is as follows: (1) The indenter is pressed into the sample by an accurately controlled test force. (2) The force is maintained for a specific dwell time, normally 10-15 seconds. (3) After the dwell time is complete, the indenter is removed leaving a round indent in the sample. (4) The size of the indent is determined optically by measuring two diagonals of the round indent using either a portable microscope or one that is integrated with the load application devices. (5) The Brinell hardness number is a function of the test force divided by the curved surfaced area of indent. The indentation is considered to be spherical with a radius equal to half the diameter of the ball. The average of the two diagonals is used in the following formula to calculate the Brinell hardness. Lesson two Figure B.1 ?Brinell hardness test Lesson two Applications Because of the wide test force range the Brinell test can be used on almost any metallic material. The part size is only limited by the testing instrument, s capacity. Strengths (1) One scale covers the entire hardness range,