PSI - Issue 12

Lorenzo Bergonzi et al. / Procedia Structural Integrity 12 (2018) 392–403 Lorenzo Bergonzi / Structural Integrity Procedia 00 (2018) 000 – 000

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1. Introduction

Material testing is fundamental to certify the mechanical properties of materials and the quality of products. In particular, uniaxial tensile test is the most frequently used method in various industrial sectors. The increase of the qualitative standards required by plastic and rubber markets, in particular, combined with the broad use of polymers for structural applications, leads to a growing need for qualification, also in terms of mechanical behavior. Such a demand is stronger in fields where the finished good is produced through a chemical-physical transformation starting from a raw material (e.g. injection molding, sintering, additive manufacturing ...). With the forthcoming concepts of Smart Factories and Industry 4.0, testing and measurement is moving away from laboratories and getting closer to the production floor, Frost & Sullivan (2016). It is therefore necessary to simplify and speed up qualifying procedures and equipment to provide accurate and reliable results in such a way that they can also be adopted by non-specialized personnel, improving the efficiency of manufacturing operations. From these considerations, it comes the MaCh 3D project showed in Figure 1, a miniaturized tensile testing machine that can be used directly alongside the production line. One of the main objectives of the project is to simplify all tensile testing activities: this requires the design of a specimen, shown in Figure 1, with non-standard geometry, and the related fixtures to apply the tensile load. In several works Liu, et al., (2017); Husain, et al., (2004); Kumar, et al., (2014); Kumar, et al., (2016), the need and the development of specimen geometries alternative to the standard one is treated, focusing on methods to obtain smaller samples compared to standard. This interest in developing different geometries highlights how non standardized specimens have already been implemented and accepted by the scientific community, given the demonstration of compatibility with the results obtained following the traditional procedures. Great interest has been generated by development of specimens dedicated to AM (Additive Manufacturing), in particular for metallic materials, as this production method requires a high number of tests for material characterization and repeated several times to assess consistency of material mechanical performances. An example is the work of Nicoletto, (2017), in which an alternative geometry is proposed in order to produce a sample for the fatigue characterization of metal powder bed fused alloys, using a fraction of the material necessary for standard specimens. In most cases, specimens with unconventional geometry are installed on traditional UTM (Universal Testing Machines) by means of special adapters that allow them to be tensioned. One of the few examples of design of an ad hoc miniaturized machine is reported in the work of Lim & Kim, (2013), which deals with the design of a miniaturized tensile testing machine with similar constructional and operating aspects to the project that has been developed.

Figure 1. MaCh 3D 5 Beta, a miniaturized tensile testing machine with its principal components.