Abstract
Fracture toughness measures the resistance of a material to fracture. This fundamental property is used in diverse engineering designs including mechanical, civil, materials, electronics and chemical engineering applications. In spite of the advancements made in the past 40 years, the evaluation of this remains challenging for extremely heterogeneous materials such as composite concretes. By taking advantage of the optical properties of a thin birefringent coating on the surface of opaque, notched composite concrete beams, here we sense the evolution of the maximum shear stress distribution on the beams under loading. The location of the maximum deviator stress is tracked ahead of the crack tip on the experimental concrete samples under the ultimate load, and hence the effective crack length is characterised. Using this, the fracture toughness of a number of heterogeneous composite beams is evaluated and the results compare favourably well with other conventional methods using combined experimental and numerical/analytical approaches. Finally a new model, correlating the optically measured shear stress concentration factor and flexural strength with the fracture toughness of concretes is proposed. The current photonics-based study could be vital in evaluating the fracture toughness of even opaque and complex heterogeneous materials more effectively in future.
Highlights
Concrete is one of the most complex group of heterogeneous engineering materials used abundantly in the world
Based on the effective crack/notch model. Further comparison of this based on the effective crack model taking into account the shear stresses in mode-1 and the subsequent evaluations of the strain energy release rate for all the samples including the 90 days cured samples are summarised in the Supplementary
We have shown an innovative method of assessing the fracture toughness of opaque heterogeneous concrete mixes in this work using the principles of photonics
Summary
Concrete is one of the most complex group of heterogeneous engineering materials used abundantly in the world. To improve the mechanical properties of concretes and reduce the usage of natural aggregates, other host materials such as fibre reinforcements[2], cementitious materials[3] and grains derived from the municipal wastes as partial substitutes for aggregates[4, 5] are being utilised in the construction sector This makes standardising the mechanical analysis of such heterogeneous materials even more challenging. The effective crack depth accounts for the location of this crack processing zone ahead of the notch tip (in addition to the initial depth of the notch (Fig. 1)) This is not easy to determine for the complex heterogeneous composite mixes.
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