The purpose of this review is to discuss the development and the state of the art in dynamic testing techniques and dynamic mechanical behaviour of rock materials. The review begins by briefly introducing the history of rock dynamics and explaining the significance of studying these issues. Loading techniques commonly used for both intermediate and high strain rate tests and measurement techniques for dynamic stress and deformation are critically assessed in Sects. 2 and 3. In Sect. 4, methods of dynamic testing and estimation to obtain stress–strain curves at high strain rate are summarized, followed by an in-depth description of various dynamic mechanical properties (e.g. uniaxial and triaxial compressive strength, tensile strength, shear strength and fracture toughness) and corresponding fracture behaviour. Some influencing rock structural features (i.e. microstructure, size and shape) and testing conditions (i.e. confining pressure, temperature and water saturation) are considered, ending with some popular semi-empirical rate-dependent equations for the enhancement of dynamic mechanical properties. Section 5 discusses physical mechanisms of strain rate effects. Section 6 describes phenomenological and mechanically based rate-dependent constitutive models established from the knowledge of the stress–strain behaviour and physical mechanisms. Section 7 presents dynamic fracture criteria for quasi-brittle materials. Finally, a brief summary and some aspects of prospective research are presented.

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A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials

Experimental and modeling study of dynamic mechanical properties of cement paste, mortar and concrete

An experimental investigation is conducted to study the quasi-static and dynamic fracture behaviour of sedimentary, igneous and metamorphic rocks The notched semi-circular bending method has been employed to determine fracture parameters over a wide range of loading rates using both a servo-hydraulic machine and a split Hopkinson pressure bar The time to fracture, crack speed and velocity of the flying fragment are measured by strain gauges, crack propagation gauge and high-speed photography on the macroscopic level Dynamic crack initiation toughness is determined from the dynamic stress intensity factor at the time to fracture, and dynamic crack growth toughness is derived by the dynamic fracture energy at a specific crack speed Systematic fractographic studies on fracture surface are carried out to examine the micromechanisms of fracture This study reveals clearly that: (1) the crack initiation and growth toughness increase with increasing loading rate and crack speed; (2) the kinetic energy of the flying fragments increases with increasing striking speed; (3) the dynamic fracture energy increases rapidly with the increase of crack speed, and a semi-empirical rate-dependent model is proposed; and (4) the characteristics of fracture surface imply that the failure mechanisms depend on loading rate and rock microstructure

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Quasi-static and dynamic fracture behaviour of rock materials: phenomena and mechanisms

Mode I fracture toughness determination with straight notched disk bending method

Influence of strain rate and water content on mechanical behavior of dam concrete

Effect of loading rate on crack velocities in HSC

Three-point bending tests on notched beams of a high-strength concrete have been conducted using both a servohydraulic machine and a self-designed drop-weight impact device. The fracture energy and the peak load were measured over a wide range of loading point displacement rates (for simplicity, it is substituted by loading rates), spanning eight orders of magnitude. Under low displacement rates, from 10 -4 mm/s to 10 mm/s, the tests were performed with the servo-hydraulic machine; from 10 2 mm/s to 10 3 mm/s we used the drop-weight impact machine. The results show that the fracture energy and the peak load increase as the loading rate increases. Nevertheless, such a trend is relatively slight under low rates and can be attributed to viscous effects mainly originating from the presence of water in the pore structure. Under high rates the increases in the fracture energy and in the peak load are dramatic due to the effect of inertia.

Fracture energy of high-strength concrete under different loading rates

Compared with the extensive research on properties of the fracture process zone (FPZ) under quasi-static loading conditions, much less information is available on its dynamic characterization, especially for high-strength concrete (HSC). This paper presents the very recent results of an experimental program aimed at disclosing the loading rate effect on the size and velocity of the (FPZ) in HSC. Eighteen three-point bending specimens were conducted under a wide range of loading rates from from 10 -4 mm/s to 10 3 mm/s using either a servo-hydraulic machine or a self-designed drop-weight impact device. Four strain gauges mounted along the ligament of the specimen were used to measure the FPZ size. Surprisingly, the FPZ size remains almost constant (around 20 mm) when the loading rate varies seven orders of magnitude.

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Size of the Fracture Process Zone in High-Strength Concrete at a Wide Range of Loading Rates

For cementitious materials, the inelastic zone around a crack tip is termed as fracture process zone (FPZ) and dominated by complicated mechanism, such as microcracking, crack deflection, bridging, crack face friction, crack tip blunting by voids, crack branching, and so on. Due to the length of the FPZ is related with the characteristic length of the cementitious materials, the size, extent and location of the FPZ has been the object of countless research efforts for several decades. For instance, Cedolin et al. (1) have used an optical method based on the moire interferometry to determine FPZ in concrete. Castro-Montero et al. (2) have applied the method of holographic interferometry to mortar to study the extension of the FPZ. The advantage of the interferometry method is that the complete FPZ can be directly observed on the surface of the sample. Swartz et al. (3) has adopted the dye penetration technique to illustrate the changing patterns observed as the crack progress from the tensile side to the compression side of the beam. Moreover, acoustic emission (AE) is also an experimental technique well suited for monitoring fracture process. Haidar et al. (4) and Maji et al. (5) have studied the relation between acoustic emission characteristics and the properties of the FPZ. Compared with the extensive research on properties of the FPZ under quasi-static loading conditions, much less information is available on its dynamic characterization, especially for high-strength concrete (HSC). This paper presents the very recent results of an experimental program aimed at disclosing the loading rate effect on the size and velocity of the (FPZ) in HSC. Eighteen three-point bending specimens were conducted under a wide range of loading rates from from 10 -4 mm/s to 10 3 mm/s using either a servo-hydraulic machine or a self-designed drop-weight impact device. The beam dimensions were 100 mm�100 mm in cross section, and 420 mm in length. The initial notch-depth ratio was approximately 0.5, and the span was fixed at 300 mm during the tests. Four strain gauges mounted along the ligament of the specimen were used to measure the FPZ size. Surprisingly, the FPZ size remains almost constant (around 20 mm) when the loading rate varies seven orders of magnitude. This is clearly different from NSC, in which the FPZ size actually decreased with loading rate.

Evolution of the fracture process zone in high-strength concrete under different loading rates


 This work presents an experimental-numerical approach aimed at determining the chip-tool contact length during orthogonal cutting of annealed AISI 4340 steel (223 HV) with TiN coated tungsten carbide inserts. Initially, pin on disc tests were performed, followed by orthogonal cutting tests. The components of the cutting force were used to calculate the coefficient of friction in orthogonal cutting and its value was compared with those obtained under sliding. Moreover, the cutting force components obtained experimentally were used to assess the reliability of the finite element model, used to estimate the temperature in cutting zone. The contact length between chip and rake face was calculated based on the experimental feed force and shear strength of the work material and was compared with the results provided by an analytical model. The experimental-numerical approach can be considered more accurate due to the fact that it considers the effect of the tool-chip interface temperature on the shear strength of the work material. However, the analytical model is quite straightforward, since it only requires the values of chip thickness and undeformed chip thickness to estimate the tool-chip contact length.

M. Cámara

Papers

Effect of loading rate on crack velocities in HSC

Fracture energy of high-strength concrete under different loading rates

Size of the Fracture Process Zone in High-Strength Concrete at a Wide Range of Loading Rates

Evolution of the fracture process zone in high-strength concrete under different loading rates

Determination of the chip-tool contact length in orthogonal cutting