Deformation and fracture of carbonaceous materials using in situ micro-mechanical testing

Liu, Dong; Flewitt, Peter E J

doi:10.1016/j.carbon.2016.11.084

Cited by 28 publications

(20 citation statements)

References 44 publications

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“…However, as noted above, measurements on micrometre-size samples, which exclude the effects of the macro- and micro-size pores, give strength numbers for this material closer to 1,000 MPa, which, as depicted in Supplementary Fig. 2, provide, in some sense, a ‘truer’ representation of the inherent strength of the actual graphitized material9. The principal conclusion here is that Raman measurements indicate a significant relief of residual tensile stresses of at least 20% of the flexural strength when the graphite is heated to 800 °C.…”

Section: Resultsmentioning

confidence: 66%

Damage tolerance of nuclear graphite at elevated temperatures

et al. 2017

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Nuclear-grade graphite is a critically important high-temperature structural material for current and potentially next generation of fission reactors worldwide. It is imperative to understand its damage-tolerant behaviour and to discern the mechanisms of damage evolution under in-service conditions. Here we perform in situ mechanical testing with synchrotron X-ray computed micro-tomography at temperatures between ambient and 1,000 °C on a nuclear-grade Gilsocarbon graphite. We find that both the strength and fracture toughness of this graphite are improved at elevated temperature. Whereas this behaviour is consistent with observations of the closure of microcracks formed parallel to the covalent-sp2-bonded graphene layers at higher temperatures, which accommodate the more than tenfold larger thermal expansion perpendicular to these layers, we attribute the elevation in strength and toughness primarily to changes in the residual stress state at 800–1,000 °C, specifically to the reduction in significant levels of residual tensile stresses in the graphite that are ‘frozen-in’ following processing.

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Section: Resultsmentioning

confidence: 66%

Damage tolerance of nuclear graphite at elevated temperatures

et al. 2017

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“…A major drawback of this approach is the time-consuming specimen preparation, which typically results in a relatively small number of specimens tested. One should keep in mind that on the micrometre length scale high scatter of measured mechanical properties can be expected [23,24] and that a large number of tests need to be performed for the measurements to be statistically reliable. Herein a different approach is proposed.…”

Section: Introductionmentioning

confidence: 99%

Combined experimental and numerical study on micro-cube indentation splitting test of cement paste

Zhang

Šavija

Schlangen

2018

Engineering Fracture Mechanics

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The aim of this paper is to investigate the fracture performance of cement paste at micro scale by both experimental and numerical methods. Micro cubic specimens with length of 100 µm were fabricated by precision cutting, grinding and micro-dicing, and tested by splitting with a wedge tip mounted on a nano-indenter. A nominal splitting tensile strength was derived from the maximum load of the recorded load-displacement diagram to represent the global fracture performance of the fractured micro-cube. To achieve this, an analogy was made between the microcube indentation splitting test and the standard Brazilian splitting test. To cope with the inherent heterogeneity of this material at micro scale, for cement paste with each water/cement (w/c) ratio (0.3, 0.4 and 0.5), more than hundred micro-cube specimens were fabricated, tested and analysed using Weibull statistics. The analysis shows that the splitting tensile strength of cement paste on the micro scale is much higher than on the macroscopic scale but lower than tensile strength of distinct hydrated cement phases measured on micro or nano scale. Furthermore, higher and less scattered values of splitting tensile strength were observed for the specimens with lower w/c ratio. In parallel with the experiments, a micro-structure informed lattice fracture model was adopted to simulate the fracture process of the micro-cube under indentation splitting. The simulated results were compared with the experimental one and have a good consistency in terms of the load-displacement curve and fracture pattern. With the method presented in this paper the framework for validation of the modelling results at micro scale is created.

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“…Recently, several authors have proposed measuring the tensile strength of cement paste [ 27 ] and it’s individual phases [ 28 ] using micro-cantilever bending tests. This technique has been previously used for micromechanical testing of other quasi-brittle materials such as e.g., nuclear graphite [ 29 , 30 ]. This technique involves focused ion milling of a cantilever beam in the material, typically in the size range of up to 10 µm.…”

Section: Experimental Programmentioning

confidence: 99%

“…A major drawback of this approach is the fact that specimen preparation is very time consuming, so a relatively small number of specimens can be prepared and analyzed. Keeping in mind that on the µm length scale high scatter of measured mechanical properties can be expected [ 29 , 30 ] and that a large number of tests need to be performed for the measurements to be statistically reliable, herein a different approach is followed.…”

Section: Experimental Programmentioning

confidence: 99%

Influence of Microencapsulated Phase Change Material (PCM) Addition on (Micro) Mechanical Properties of Cement Paste

2017

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Excessive cracking can be a serious durability problem for reinforced concrete structures. In recent years, addition of microencapsulated phase change materials (PCMs) to concrete has been proposed as a possible solution to crack formation related to temperature gradients. However, the addition of PCM microcapsules to cementitious materials can have some drawbacks, mainly related to strength reduction. In this work, a range of experimental techniques has been used to characterize the microcapsules and their effect on properties of composite cement pastes. On the capsule level, it was shown that they are spherical, enabling good distribution in the material during the mixing process. Force needed to break the microcapsules was shown to depend on the capsule diameter and the temperature, i.e., whether it is below or above the phase change temperature. On the cement paste level, a marked drop of compressive strength with increasing PCM inclusion level was observed. The indentation modulus has also shown to decrease, probably due to the capsules themselves, and to a lesser extent due to changes in porosity caused by their inclusion. Finally, a novel micro-cube splitting technique was used to characterize the tensile strength of the material on the micro-meter length scale. It was shown that the strength decreases with increasing PCM inclusion percentage, but this is accompanied by a decrease in measurement variability. This study will contribute to future developments of cementitious composites incorporating phase change materials for a variety of applications.

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Deformation and fracture of carbonaceous materials using in situ micro-mechanical testing

Cited by 28 publications

References 44 publications

Damage tolerance of nuclear graphite at elevated temperatures

Damage tolerance of nuclear graphite at elevated temperatures

Combined experimental and numerical study on micro-cube indentation splitting test of cement paste

Influence of Microencapsulated Phase Change Material (PCM) Addition on (Micro) Mechanical Properties of Cement Paste

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