Article

The Charpy impact test and its applications

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Abstract

THIS PAPER REVIEWS the Charpy V-notch (CVN) impact test and assesses its utility to characterize fracture resistance in applications to modern tough materials in contrast to those encountered prior to the availability of such materials.The origin of the CVN test and its development into a standard for use with metallic materials is discussed, with brief reference also made to application-based standards for use with other engineering materials. Thereafter, the evolution of mechanical and other properties motivated by industry demands is illustrated in regard to strength and toughness.The interpretation of the CVN test in regard to ( 1 ) the force-displacement and compliance response that develops during the test, and (2) factors affecting the energy measured and controlling failure of the CVN specimen, are discussed, including the tup design and the use of sub-size specimens.The utility of CVN testing is illustrated and discussed in the context of pipeline and other applications involving tough steels. Finally, the implications of evolution in material properties is assessed for impact-test practices including ASTM E23 and ISO 148-1, which are specific to the CVN practice, and the drop-weight tear test. It is concluded that where tough materials are involved, alternative testing practices are needed that are better adapted to the specific loading and failure response of the structure of interest.

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... For this reason a systematic study is needed to understand the cause of this double-clustered response. While it can be argued that the utility of the CVN test in quantifying fracture behavior is long past (31) , the same can be argued for all of the same reasons for the DWTT (31) . That said, the DWTT does not provide an alternative path forward such that issues with each test in its respective historic role must be addressed. ...
... For this reason a systematic study is needed to understand the cause of this double-clustered response. While it can be argued that the utility of the CVN test in quantifying fracture behavior is long past (31) , the same can be argued for all of the same reasons for the DWTT (31) . That said, the DWTT does not provide an alternative path forward such that issues with each test in its respective historic role must be addressed. ...
Conference Paper
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... When the sample is unable to withstand more energy, a fracture occurs. Hard materials absorb more energy, before fracture than brittle materials [3]. Nanomaterials have emerged as a class of materials that have at least one dimension at nano-size. ...
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... To simulate attrition between grains during saltation while isolating the effects of impact energy on mass attrition, we examine the amount of mass lost due to collisions between two grains. Our experiment bears some similarity to the Charpy impact test (Leis, 2013) -a standard technique for measuring the energy absorbed by a material (typically metal) in producing fracture -but has modified boundary conditions and geometry to better approximate binary bed-load collisions. Although collisions in water can be viscously damped, for sufficiently large grains (> 10 −2 m) these collisions are semi-elastic and independent of the fluid (Schmeeckle et al., 2001). ...
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... We therefore used a Charpy impact tester as shown in Fig. 1e-g. This test in industry is a standardized high strain-rate test which measures a material resistance for fracture (e.g., Leis 2013). The present Charpy impact test involves striking a rock sample fixed in a bottom holder with a pendulum containing the same kind of rock in its holder at a predetermined height. ...
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... This test in industry is a standardized high strain-rate test which measure a material resistance for fracture (e.g. Leis, 2013). The present Charpy impact test involves striking a rock sample xed in a bottom holder with a pendulum containing the same kind of rock in its holder at a predetermined height. ...
Preprint
Full-text available
Several laboratory experimental studies of photoemission characteristics of rocks as they fracture have been conducted to elucidate the mechanism of earthquake lightning (EQL). In most of these studies, granite, which exhibits remarkable photoemission, is widely used to explain the mechanism attributed to the piezoelectric effect or piezo-induced effect of quartz, a constituent mineral of granite. Photoemission induced by rock fracturing has been observed prominently during landslides caused by earthquakes. According to the literature on historical earthquakes, landslide-induced EQL was witnessed even at locations where quartz was not present. In this study, we therefore studied the physicochemical characteristics of photoemissions associated with impact shear fractures in various rocks, selected based on historical earthquake records of landslide EQL. As a result, we could highlight various physicochemical processes associated with the frictional heating generated during shear impacts between rocks.
... Charpy data from many pipeline steels can be found in Refs. [17][18][19]. ...
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Full-text available
Propagating shear failure can occur in gas and certain hazardous liquid transmission pipelines, potentially leading to a large long-burning fire and/or widespread pollution, depending on the transported product. Such consequences require that the design of the pipeline and specification of the steel effectively preclude the chance of propagating shear failure. Because the phenomenology of such failures is complex, design against such occurrences historically has relied on full-scale demonstration experiments coupled with empirically calibrated analytical models. However, as economic drivers have pushed toward larger diameter higher pressure pipelines made of tough higher-strength grades, the design basis to ensure arrest has been severely compromised. Accordingly, for applications where the design basis becomes less certain, as has occurred increasing as steel grade and toughness has increased, it has become necessary to place greater reliance on the use and role of full-scale testing. This paper explores the factors controlling design to avoid propagating shear failure, to identify critical gaps in the understanding and analyses used in design. It then considers these aspects with a focus on the significance of design factor and grade. Finally, this paper considers the implications of steel chemistry and processing to achieve higher grades - which as the window on production controls closes can necessitate a more comprehensive full-scale testing program to confirm arrestability under typical production conditions.
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Conference Paper
The consequences of a dynamic fracture in a gas-transmission pipeline require that pipelines be designed to avoid such incidents at a high level of certainty. For this reason, the related phenomonology has been studied since the early 1970s when the possibility of a dynamic ductile fracture was recognized. Full-scale experiments were done to characterize the fracture and gas dynamics associated with this process and empirical models were developed as a means to represent these experiments in a design or analysis setting. Such experiments focused on pure methane gas, and in the early days used steels with toughnesses less than 100 J, consistent with the steel making capabilities of the 1970s. Subsequently, interest shifted to larger diameter, higher pressure, higher BTU “rich” gases requiring higher toughness steels. The full-scale tests conducted to validate the arrest toughness levels determined that these empirical models were non-conservative. This paper presents a relationship between the dynamic crack propagation resistance and the apparent crack propagation resistance as measured by Charpy vee-notch (CVN) test specimens. This relationship is used in conjunction with the existing Battelle empirical criterion for dynamic-fracture arrest to determine the apparent toughness required to arrest a propagating ductile fracture in gas-transmission pipelines. The validity of this relationship is illustrated by successful predictions of arrest toughness in pipelines under a range of conditions including rich gases and high-toughness steels, including those showing a rising upper-shelf behavior.
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Charpy impact testing is a low-cost and reliable test method which is commonly required by the construction codes for fracture-critical structures such as bridges and pressure vessels. Yet, it took from about 1900 to 1960 for impact-test technology and procedures to reach levels of accuracy and reproducibility such that the procedures could be broadly applied as standard test methods. This paper recounts the early history of the impact test and reports some of the improvements in the procedures (standard specimen shape, introduction of a notch, correlation to structural performance in service, and introduction of shrouds) that led to this broad acceptance.
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Article
High power beam welds, such as electron beam welds or laser welds, sometimes provide fracture path deviation (FPD) in standardized Charpy V-notch fracture toughness testing due to narrow bead profile together with higher overmatching in strength between weld metal and base metal. Moreover it should be noted that these typical features of beam welds might result in a plastic constraint loss around both the notch and crack tip in fracture toughness test specimens. Even in the temperature range where FPD would not occur the fracture toughness test results could not necessarily be an intrinsic value of such beam welds. These fracture properties make it difficult to evaluate fracture performance of girth welded pipe joints. In this paper the estimation method of intrinsic fracture toughness of beam weld metal itself using standard toughness test specimens is proposed on the basis of "Weibull stress criterion." The predicted intrinsic fracture toughness was found to be lower than the test results both in standard Charpy specimen and in three-point bend specimen with fatigue precrack. The assessment of brittle fracture performance of girth welded pipeline was conductedfirom the estimated intrinsic fracture toughness of girth welds by means of Weibull stress criterion. It was demonstrated that the low intrinsic fracture toughness of beam welds could not directly lead to the low fracture performance of a pipe joint under tensile loading. This is because of a lower plastic constraint compared to a three-point bend specimen due to difference in loading mode together with constraint loss in pipe joints and shielding effect of straining in weld metal due to highly overmatched narrow welds.
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