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Session 1664

A Novel Approach to Hardness Testing

F. Xavier Spiegel, Harvey A. West, 11 Loyola College/Materials Analytical Services

Key Words: Hardness, rebound, scleroscope, coefficient of restitution

Prerequisite Knowledge: Knowledge of physical testing of metallic materials

Objective: To demonstrate a simple rebound hardness measuring device and explore its applications and limitations.

Equipment: 1. Rebound hardness tester as outlined in Reference 1. 2. Several metallic samples of various compositions and harnesses.

Introduction: This paper gives a description of the application of a simple rebound time measuring device and relates the deterrniniition of relative hardness of a variety of common engineering metals. A relation between rebound time and hardness will be sought; hardness is the ability of a material to resist permanent deformation and is typically quantified by relating the geometry of an indentor and normal force applied to the depth of penetration. The effect of specimen geometry and surface condition will also be discussed in order to acquaint the student with the problems associated with rebound hardness testing.

Procedure: A complete description of the construction of the apparatus is contained in Reference 1. This device, constructed for under $100, is designed to repeatedly drop a 5.59 mm (0.220 in.) diameter ball from a fixed height of 9.0 cm (3.54 in.) onto a metal specimen clamped to a rigid base. A microphone coupled through an operational amplifier precisely relays the initial contact and subsequent rebound contact. A timing circuit is used to measure the interval between these events and calculates the rebound time, relatable to the coefficient of restitution of materials, a dimensionless quantity which is the negative of the relative velocity of two objects after a collision, divided by their relative velocity before the collision.

$iiii’ ) 1996 ASEE Annual Conference Proceedings ‘.%,~y~’;:

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West, H. A., & Spiegel, F. X. (1996, June), A Novel Approach To Hardness Testing Paper presented at 1996 Annual Conference, Washington, District of Columbia. 10.18260/1-2--6213