Editorial: Special Issue on Mechanical Characterization of Small Scale Specimens
Authors: Lancaster Robert , Jeffs Spencer 
Published: October 2022

The development and adoption of nonconventional and small scale mechanical test methods has risen in recent decades. This has primarily been driven by the requirement to measure mechanical properties at smaller length scales to enable an assessment of remnant life capabilities, alloy-down selection, and localized property sampling of larger complex components. This development is typified by the small punch (SP) test, one of the most prominent forms of these smaller scale approaches, which is receiving widespread attention from a multitude of industrial sectors that recognize the significant cost benefits it has to offer. With numerous worldwide laboratories now utilizing the SP test for material characterization for all manner of purposes, this growing interest and exploitation led to the recent formulation of an ASTM standard (2020) and equivalent EN standard (2021), illustrating the role that small scale testing has in the wider testing community. Indeed, other methods now being adopted include miniaturized uniaxial, shear punch, hydraulic bulge, small ring, and impression testing. This list is by no means exhaustive, however, with many more innovative techniques now being developed. This special issue of ASTM International’s journal Materials Performance and Characterization showcases the diversity and innovative nature of the research that is currently developing across the world on a broad scope of materials and applications in this ever-expanding field. It is with great pleasure that the guest editors present this Special Issue on Mechanical Characterization of Small Scale Specimens. The call for papers attracted a large number of abstracts from leading scientists, engineers, and researchers from a wide range of international institutions. After scrutiny and their acceptance, a total of 10 full-length research articles have been included in the final issue. The issue opens with two articles on SP testing. The first paper is written Dr. Martin Abendroth and colleagues; Dr. Abendroth of Freiburg University is a highly esteemed figure in the world of small scale testing who has applied the SP test to investigate the properties of iron-based shape memory alloys. Dr. Abendroth’s team are the first to attempt this, and this paper is certainly one of the highlights of the issue. The second article on SP testing is written by Dr. Romy Welschen—a nuclear materials scientist at the Nuclear Research and Consultancy Group (NRG) in Petten—and colleagues, who presents a novel SP test fabrication and setup that works under hot-cell conditions for evaluating the properties of irradiated materials, another article of particular interest to the SP testing community. The third contribution is made by Prof. Steve Brett, an honorary professor of the University of Nottingham and prominent member of the small scale testing community, and colleagues on the recent developments in creating a workshop agreement on impression creep testing. Prof. Brett has worked in this field for the past two decades and has led the efforts in formally standardizing the test procedure and making it accessible to a wider group of researchers. The next three papers focus on the use of miniature creep specimens and their application in deriving the high temperature properties of in-service materials. Two of these three papers are written by Dr. Akito Nitta’s team from Kobe Material Testing Laboratory in Tokyo, who firstly extracted miniature creep specimens from the wall of a service exposed boiler tube and were able to evaluate the internal pressure creep rupture life. The second paper from the same team was able to successfully correlate the stress–rupture behavior of an ultra-miniature creep specimen to the behavior generated from more standard test approaches. The final paper on this theme was submitted by Dr. Masatsugu Yaguchi from the Central Research Institute of Electric Power Industry, also located in Tokyo. Dr. Yaguchi has been researching high temperature damage mechanisms for the past 30 years, and Dr. Yaguchi’s contribution proposes a remaining creep life prediction method for Grade 91 steel weldments, as derived from small scale specimens taken from the base metal rather than the weld itself. The next two contributions look at the application of miniaturized tensile testing. The first of these is a contribution provided by Dr. Sreekar Karnati of Missouri University of Science and Technology and colleagues, who utilized a tensile specimen design that is 1/230th of the volume of the smallest ASTM recommended tensile geometry and coupled this with digital image correlation for localized strain mapping. The second paper is written by Prof. Hezong Li of Hebei University of Engineering and colleagues, and it focuses on the use of interrupted miniature tensile tests to understand the fracture evolution mechanisms of a Grade 91 steel at elevated temperature. The ninth contribution is provided by Prof. Shin-ichi Komazaki of Kagoshima University and colleagues, another key member of the growing small scale testing community of researchers. This paper details the use of a new fatigue testing method–the small bulge fatigue test–where oil is used to exert a load on the miniaturized test sample and utilizes the test method to examine the suitability of the approach in assessing fatigue damage of actual pre-exposed in-service components. The tenth and final paper is provided by Dr. Noritake Hiyoshi, an associate professor at the University of Fukui, and colleagues, and it details the efforts in compiling a standard for the miniature testing of solders and emphasizes the importance of why such a standard is needed in this field. The guest editors would like to express their sincere gratitude to all authors and reviewers who have provided contributions to this special issue. Without their high-level research and excellent contributions, this special issue would not have been possible. Finally, we wholeheartedly thank Alyssa Conaway of ASTM International for handling issues related to the process of publishing an outstanding journal. It has been a long process, but the guest editors are delighted with the final collection of articles that have been compiled. We sincerely hope that you enjoy these papers and look forward to engaging with you in future research projects and international events. Best regards, Prof. Robert Lancaster Dr. Spencer Jeffs