On the Processing of Spalling Experiments. Part II: Identification of Concrete Fracture Energy in Dynamic Tension

• Published in: Journal of dynamic behavior of materials 2018-03, Vol.4 (1), p.56-73
• Main Authors: Lukić, Bratislav B., Saletti, Dominique, Forquin, Pascal
• Format: Article
• Language: English
• Subjects: Axial stress; Chemistry and Materials Science; Computer simulation; Concrete; Cracking (chemical engineering); Cracking (fracturing); Damage assessment; Data processing; Elasticity; Energy measurement; Fracture mechanics; Fracture toughness; High strain rate; Materials Science; Measurement techniques; Metallic Materials; Solid Mechanics; Spalling; Temporal resolution
• ISSN: 2199-7446; 2199-7454
• DOI: 10.1007/s40870-017-0138-y

This paper presents a second part of the study aimed at investigating the fracture behavior of concrete under high strain rate tensile loading. The experimental method together with the identified stress–strain response of three tests conducted on ordinary concrete have been presented in the paper entitled Part I (Forquin and Lukić in Journal of Dynamic Behavior of Materials, 2017. https://doi.org/10.1007/s40870-017-0135-1 ). In the present paper, Part II, the investigation is extended towards directly determining the specific fracture energy of each observed fracture zone by visualizing the dynamic cracking process with a temporal resolution of 1 µs. Having access to temporal displacement fields of the sample surface, it is possible to identify the fracture opening displacement (FOD) and the fracture opening velocity of any principle (open) and secondary (closed) fracture at each measurement instance, that may or may not lead to complete physical failure of the sample. Finally, the local Stress-FOD curves were obtained for each observed fracture zone, opposed to previous works where indirect measurements were used. The obtained results indicated a much lower specific fracture energy compared to the results often found in the literature. Furthermore, numerical simulations were performed with a damage law to evaluate the validity of the proposed experimental data processing and compare it to the most often used one in the previous works. The results showed that the present method can reliably predict the specific fracture energy needed to open one macro-fracture and suggested that indirect measurement techniques can lead to an overestimate of specific fracture energy due to the stringent assumption of linear elasticity up-to the peak and the inability of having access to the real post-peak change of axial stress.