Small specimen techniques for estimation of tensile, fatigue, fracture and crack propagation material model parameters

Abstract

Small specimen mechanical testing is an exciting and rapidly developing field in which fundamental deformation behaviours can be observed from experiments performed on comparatively small amounts of material. These methods are particularly useful when there is limited source material to facilitate a sufficient number of standard specimen tests, if any at all. Such situations include the development of new materials or when performing routine maintenance/inspection studies of in-service components, requiring that material conditions are updated with service exposure. The potentially more challenging loading conditions and complex stress states experienced by small specimens, in comparison with standard specimen geometries, has led to a tendency for these methods to be used in ranking studies rather than for fundamental material parameter determination. Classifying a specimen as ‘small’ can be subjective, and in the present work the focus is to review testing methods that utilise specimens with characteristic dimensions of less than 50 mm. By doing this, observations made here will be relevant to industrial service monitoring problems, wherein small samples of material are extracted and tested from operational components in such a way that structural integrity is not compromised. Whilst recently the majority of small specimen test techniques development have focused on the determination of creep behaviour/properties as well as sub-size tensile testing, attention is given here to small specimen testing methods for determining specific tensile, fatigue, fracture and crack growth properties. These areas are currently underrepresented in published reviews. The suitability of specimens and methods is discussed here, along with associated advantages and disadvantages.

Assessment of Additive Manufactured IN 625’s Tensile Strength Based on Nonstandard Specimens

“…Similarly, the variation in elongation measurements between the two types of test specimens (standard and sub-sized) are also attributed to the size effects. This effect is also presented in the literature for other materials [54,78,80]. Another explanation for these differences may be related to the thermal exposure that is different for sub-sized and standard specimens produced by laser-based metal additive manufacturing.…”

“…As many specimens should be manufactured during the testing campaign, a significant quantity of raw material is used, which is expensive and time-consuming. Several studies focused on developing small specimen test techniques (SSTTs) [53,54] that are not limited only to AMed materials to reduce the material and time consumption as much as possible. The SSTs can achieve good consistency with the conventional test and are divided into three categories: similarity (small tensile test-STT and small compression test-SCT), penetration (small punch beam test-SPT and small shear), and semi-penetration (indentation test-IT) [55].…”

Specimen Size Effect on the Tensile Properties of Rolled Steel of Long-Term-Operated Portal Crane

“…Together with fracture toughness at quasistatic loading conditions or impact toughness, these characteristics are considered to be the basic mechanical properties of the material, and they are most often included in regulations for structural steels. The mechanical properties of steels are dependent not only on intrinsic microstructural features, such as the grain size and structure of the precipitated particles [1][2][3][4], but also on extrinsic testing conditions, such as strain rate [5,6], specimen geometry and size [4,[7][8][9][10][11][12][13], and temperature [14][15][16]. Therefore, testing conditions and the geometry and dimensions of specimens are regulated by standards [17,18].…”

Investigation of the Crack Propagation in the Graphene/Synthetic Rubber Nanocomposite Materials with DIC Technique

“…The fracture resistance and material performance of an elastomer material due to crack propagation were not apparent until research by Rivlin and Thomas based on the Griffith theory. They have created more suitable solutions by modifying the irreversibility of energy dissipation in high-stress areas near the crack tip of the elastomeric material [1,2].…”