Experimental Study of Three-Dimensional Propagation of Crack in Transparent Rock Mass

Three-dimensional crack propagation in a rock mass was investigated using a specifically designed material with good transparency and elastoplasticity. The material has properties that are similar to those of the nature sandstone. Hydromechanical tests were conducted to simulate pore pressure in the paper to study the influence of the angle of the primary crack and the water pressure on the mechanical stability of the rock mass. The results indicated that the water pressure accelerated the crack propagation and the failure of the samples. The influence of water pressure on initiation crack strength was not significant but had a significant impact on the peak strength. With the increase in water pressure, the crack initiation strength, penetration strength, and peak strength all decrease in varying degrees. The penetration strength did not only depend on the pore pressure but also exhibited high sensitivity to the inclination angle of the primary crack. The extended finite element method is used to simulate hydraulic fracturing. The simulation results show that the stress near the tip exhibited a cycle of energy accumulation-crack expansion-stress relaxation as the crack expanded, and this finding was consistent with Griffith’s energy theory.

An experimental study on the damage and acoustic emission character of raw coalunder uniaxial compression condition

In the paper, the acoustic emission character is analyzed using a new damage variable which is defined based on ring-down count or energy count of acoustic emission and the damage model of raw coal under uniaxial compression is thus established. The results show that acoustic emission information can reflect inter?nal damage of raw coal and is closely related with primary crack compression and evolutionary course of new crack generation, growth, and connectivity.

Steel stress patterns between two primary cracks in concrete

The national and international codes and standards and the literature consider the stress patterns either in case of a single crack or of equidistant primary cracks which developed at the same load level. Moreover, most FE models consider smeared cracks which do not allow for any insight in the real inner behavior of structural concrete. This paper considers the stochastic character of the concrete tensile strength’s distribution along the reinforced concrete element and a realistic local bond stress vs. slip relationship with its hysteretic character when the sign of local slip changes due to the occurrence of a new primary crack.

Influence of Rock Strength on the Propagation of Slotted Cartridge Blasting-Induced Directional Cracks

Based on theories of explosive mechanics and rock fracture mechanics, the influence mechanism of rock strength on the propagation length of the primary crack in the directional fracture blasting with slotted cartridge has been investigated deeply to propose the relation equation between the rock strength and the propagation length of the primary crack. Theoretically, the maximum length am of the primary crack increases with the enhancing rock strength parameters. The explicit dynamic analysis software LS-DYNA has been used to simulate the slotted cartridge blasting in the mudstone, sandstone, and granite with different strengths in order to reveal the effect of rock strength on the propagation length and velocity of the primary crack and the stress distribution characteristics in rock. The numerical results show the primary crack easily bifurcates and attain a much shorter propagation length in the mudstone with the minimum strength, and there are radial cracks appearing in the nonslotted direction. When rock strength rises, the propagation length, velocity, and duration of the primary crack and the concentration degree of effective stress in the slotted direction will all increase in the sandstone and granite, but there is an opposite influence trend of rock strength in the stage of the initial guide crack’s formation. The cracking velocity has an overall oscillation downtrend whose swing amplitude enhances clearly with the increasing rock strength, signifying the more unsteady propagation of the primary crack in the higher strength rock.

REINFORCED CONCRETE CRACK MODEL BASED ON STIFFNESS ANALYSIS OF TENSION MEMBERS

The average spacing of primary cracks in a reinforced concrete (RC) member greatly influences its in-service behavior, especially with regard to stiffness and average crack width. Accurate predictions of the average crack spacing are therefore crucial for satisfying serviceability requirements in RC structures. This is particularly the case when relying on analytical models that treat cracks discretely rather than in a smeared fashion. Popular code-based models for primary crack spacing are often wildly inaccurate and may lead to poor predictions of in-service behavior. In this paper, the problem or primary crack formation is approached from a stiffness perspective. The proposed model is based on the results of several experimental tension stiffening studies in the literature, as well as a previous numerical study dealing with the effect on stiffness of non-plane deformation in the neighborhood of primary cracks. The proposed model is compared to some popular code-based models and is shown to better predict average crack spacing for a wide variety of beams, slabs, and tension members.

Jacq Effect Influence on Thermomechanical Contact Fatigue

The paper take into account the thermo – mechanical contact fatigue as an important component of global thermo – mechanical contact wear. This phenomenon is very important for contacts localized in enclosure, working non – stop, with few possibilities of intervention. It is presented in a synthetical way the theories concerning the location of the decisive stresses for mechanical rolling contact fatigue in connection with the primary crack in deterioration . Also, are made some considerations about the thermal effect Jacq and the consequences for the temperature gradient in a metallic wall. Most of the technological processes are carried out with heat release. An illustrated example is the rolling mill process where the thermal tide is at a high level. The reability evaluation for rolling mill rollers it is in connection with the position of the primary crack under the contact surface. This position give the type of the decisive stress for destruction. The importance of the paper is the connection between the thermal effect Jacq and the thermomechanical contact fatigue. Also, the influence of the changing slope for the temperature gradient concerning the position of the primary crack under the contact surface in thermomechanical contact fatigue [1].