Mechanics of the small punch test: a review and qualification of additive manufacturing materials

Abstract

The small punch test (SPT) was developed for situations where source material is scarce, costly or otherwise difficult to acquire, and has been used for assessing components with variable, location-dependent material properties. Although lacking standardization, the SPT has been employed to assess material properties and verified using traditional testing. Several methods exist for equating SPT results with traditional stress–strain data. There are, however, areas of weakness, such as fracture and fatigue approaches. This document outlines the history and methodologies of SPT, reviewing the body of contemporary literature and presenting relevant findings and formulations for correlating SPT results with conventional tests. Analysis of literature is extended to evaluating the suitability of the SPT for use with additively manufactured (AM) materials. The suitability of this approach is shown through a parametric study using an approximation of the SPT via FEA, varying material properties as would be seen with varying AM process parameters. Equations describing the relationship between SPT results and conventional testing data are presented. Correlation constants dictating these relationships are determined using an accumulation of data from the literature reviewed here, along with novel experimental data. This includes AM materials to assess the fit of these and provide context for a wider view of the methodology and its interest to materials science and additive manufacturing. A case is made for the continued development of the small punch test, identifying strengths and knowledge gaps, showing need for standardization of this simple yet highly versatile method for expediting studies of material properties and optimization.

Microstructure Characterization and Small Punch Test Analysis in Nickel-Based Alloy 617 by High Energy Neon Implantation

“…The two commonly used methods are numerical simulation and the empirical correlation method. In this paper, the second method is used to correlate the characteristic data on the original load-deflection curves with the conventional test results to evaluate the changes in the tensile properties and fracture properties [22,23].…”

“…The ultimate tensile strength can reflect the changes in the tensile properties of the material. Studies have shown that the ultimate tensile strength can be estimated from two characteristic data, which are P max the maximum load, and P i the load corresponding to the deflection of 1.1 times sample thickness [22,23]. The corresponding empirical correlations have been derived to analyze the irradiation effect caused by ion and neutron irradiation for some specific materials [20].…”

“…The applicability of these correlations has been explored by some researchers. It shows that a unified empirical correlation can be used to roughly estimate the ultimate tensile strength under some different test conditions [23,24]. Therefore, it can be used to estimate ultimate tensile strength with these characteristic data, though there are no corresponding correlations for nickel-based alloys in the literature.…”

Mechanical and Tribological Behavior of Functionally Graded Unidirectional Glass Fiber-Reinforced Epoxy Composites

“…The test setup consists of a die with upper and lower parts to fix the position of the specimen and a punch with a spherical tip to penetrate the specimen under constant speed. Recently, SPT has been widely used to estimate the mechanical properties of metallic and nonmetallic materials, especially when there is no excess of materials [ 26 , 27 , 28 , 29 , 30 ].…”

Eta plastic correlation to evaluate crack tip opening displacement of pre‐cracked small punch test specimen using experimental data

“…For assessing mechanical and fracture properties, a variety of correlations have been found between standard testing and SPT data. As these correlations are based on a specific set of materials [1][2][3][4][5] and testing methods, they must be reviewed for their validity and reliability. In the absence of an initial crack in SPT specimens, the application of these correlations to predict material fracture characteristics is unreliable.…”