Abstract
Structural-temporal approach based on the notion of incubation time is used for interpretation of strain-rate effects in the fracture process of concretes and rocks. It is established that temporal dependences of concretes and rocks are calculated by the incubation time criterion. Experimentally observed different relations between ultimate stresses of concrete and mortar in static and dynamic conditions are explained. It is obtained that compressive strength of mortar at a low strain rate is greater than that of concrete, but at a high strain rate the opposite is true. Influence of confinement pressure on the mechanism of dynamic strength for concretes and rocks is discussed. Both size effect and scale effect for concrete and rocks samples subjected to impact loading are analyzed. Statistical nature of a size effect contrasts to a scale effect that is related to the definition of a spatio-temporal representative volume determining the fracture event on the given scale level.
Highlights
The behaviour of the material strength dependent on the dimensions of the specimen is problem of fracture mechanics, construction, mining engineering and other fields engineering
At the equilibrium compression material is characterized by static strength; in the case of dynamic loading the failure stress is different depending on the strain rate
It is obtained that limiting compressive stress of mortar at a low strain rate was smaller than that of concrete, but at a high strain rate the opposite is true
Summary
The behaviour of the material strength dependent on the dimensions of the specimen is problem of fracture mechanics, construction, mining engineering and other fields engineering. As referred to in [4], the incubation time is a result of relaxation processes that precede the development of micro-structural defects in the material It is a characteristic time of the fracture process invariably for any strain rate. Chasiotis and Knauss [6] observed the sensitivity of polysilicon films tensile strength to a change of specimen dimensions and identified by size and scale effects as the translation of data from micro-mechanical to macroscopic material properties and associated with the enormous influence of molecular or atomistic phenomena on the failure process of the material. According to structural-temporal approach, we evaluate the incubation time concrete and mortar plot dependences (high-speed curve) of the fracture stress on strain rate [5]. Comparisons of material strength of fixed length or width specimen are presented
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