Evolution Of Dissipated Energy Research Articles

Investigation on failure mechanism and time-delay fracturing behavior of hard-rock tunnel under extremely high geostress state

To investigate the failure mechanism and time-delay fracturing behavior of hard-rock tunnel under extremely high geostress state, a series of conventional triaxial compression tests and time-delay loading–unloading mechanical tests on rocks were conducted. Combining testing results and on-site data of deep-buried tunnels, the generation mechanism and failure process of time-delay rockbursts were analyzed. The results indicate that with the increase of confining pressure, the failure mode of hard-rock exhibits a transition from axial splitting type and shear-slip type to special squeezing-expansion type. The progressive damage of rocks under extremely high stress state mainly manifests as aging lateral and volumetric expansion. Under time-delay compression tests, the long-term strength of hard-rock is lower than the threshold stress of σeb. In extremely high stress state, the fracture and dissipated energy evolution of rocks has significant time-dependent characteristics. Under extremely high stress conditions, rocks can store a large amount of releasable energy internally and gradually generate numerous cracks without the need for external work, ultimately leading to sudden unstable failure. Affected by the superposition of time-delay pressure and loading–unloading effects, the hard-rock also exhibits the same time-dependent fracturing behavior as soft-rock under high stress state, but its deformation mechanism is dominated by lateral expansion and crack volumetric dilatancy. When the stress level is far from reaching the ultimate strength required for rockmass failure, it is sufficient to cause the propagation of internal microcracks. Under the action of time-delay loads, the spalling and peeling failure of surrounding rock is significantly reduced, but the scale of unstable blocks is larger. Based on the failure process and microseismic monitoring date of rockburst in hard-rock tunnels, the entire evolution process of time-delay rockbursts can be divided into the following six stages: before excavation, rockmss excavation, aging cracking, squeezing-expansion, instability and spalling, time-delay rockburst. Time-delay rockburst has an obvious acoustic emission calm period before its occurrence, making its incubation process has strong suddenness and randomness.

Shear fatigue behaviour of interfaces between bituminous layers using 2T3C hollow cylinder apparatus and Digital Image Correlation

Evaluating the shear fatigue behaviour of the interface between two bituminous layers is important in order to assure the structure can withstand repeated loadings. The 2T3C (Torsion-Traction-Compression sur Cylindre Creux, in French) hollow cylinder apparatus developed at the University of Lyon/ENTPE can apply torsion, tension, and compression on hollow cylinder samples. In this study, the apparatus is combined with 3D Digital Image Correlation (3D-DIC) to study the fatigue behaviour of the double-layered hollow cylinder samples with the interfaces with a tack coat made of emulsified bitumen. The fatigue failure was observed at the interfaces and not in layers. Six fatigue criteria are proposed to determine the fatigue life of an interface. They are: (1) the 50% reduction of stiffness criterion; (2) the maximal phase angle criterion, (3) maximal dissipated energy criterion, (4) slope change in the dissipated energy evolution curve criterion, (5) slope change in the stress evolution curve criterion, and (6) slope change in the displacement gap at the interface evolution curve criterion. The first criterion is more conservative in comparison with the last five criteria.

Experimental Investigation on Dissipated Energy Evolution Characteristics and Influencing Factors of Concrete under Cyclic Loading

Experimental Investigation on Dissipated Energy Evolution Characteristics and Influencing Factors of Concrete under Cyclic Loading

Impact of Depressurizing Boreholes on Energy Dissipation in Deep Roadway

Depressurizing borehole drilling is an effective approach to control the large deformation of deep roadway. It can transfer the high stress in the proximity of the roadway into the deep stable rock masses. However, it should be noted that the borehole drilling will inevitably cause the secondary damage to roadway. To determine the parameters of depressurizing boreholes, the degree of the secondary damage must be evaluated properly. Given that the rock mass failure is an unstable phenomenon driven by energy, it is of great use to reveal the disturbing impact of depressurizing boreholes on the roadway stability from the angle of energy dissipation. This is much more consistent with the failure nature of rock mass. Hence, an integrated method of laboratory test, numerical simulation, and theoretical analysis was used to study the disturbing effect of depressurizing boreholes on roadway energy dissipation. The equations of elastic energy and dissipated energy of rock cell grid were derived based on the energy principle and finite-difference algorithm, which was implemented into FLAC3D software by the FISH language. The numerical stress-strain and dissipated energy-strain curves of rock samples were verified by experimentally obtained data, and the whole deformation path from roadway excavation to instability was back-analyzed by the dissipated energy evolution. Based upon the energy model, the ratio of borehole diameter D to row spacing R ( D / R ) was selected as the variable to analyze the influence of borehole parameters on the depressurizing effect. The varying D / R leads to three depressurizing states: insufficient depressurization, sufficient depressurization, and overdepressurization. Increasing D / R will make the roadway transfer from insufficient depressurization to sufficient depressurization and finally to overdepressurization. The sufficient depressurizing state could be realized by adjusting the borehole D / R value, which is of great use to the roadway control. The D / R values of 1 : 6 to 1 : 2 were proposed for the test roadway, and D / R = 1 : 6 was applied in the field test, which achieved a well roadway control effect.

A novel energy-based model for predicting the fatigue life of the automobile sealant adhesively bonded butt joints

The evolution of dissipation energy of the uniaxial and multiaxial fatigue experiments on the automobile sealant adhesively bonded butt joints was investigated by the method of fatigue dissipation energy analysis and fatigue failure identification. The results demonstrated that the dissipation energy increased and the fatigue life decreased with the increase of stress amplitude, mean stress, and the decrease of cycle time. Meanwhile, the non-proportional loading path resulted in greater dissipation energy and shorter fatigue life than that of uniaxial and proportional loading path. Moreover, the existing energy-based model using the energy dissipated in different cyclic loading stages as the fatigue parameters were adopted to predict the fatigue life of the automobile sealant adhesively bonded butt joints, respectively. The practical limitations of the prediction model using the total dissipation energy as the fatigue parameter were evaluated. Therefore, a novel energy-based fatigue life prediction model was proposed which using the partial steady stage of dissipation energy curves as the parameters. The predicted results of the novel model and the comparison with that of the existing energy-based model indicated that the novel model had an excellent ability to predict the fatigue life, and was more practical in engineering application for the automobile sealant adhesively bonded butt joints.

Damage evolution of tuff under cyclic tension–compression loading based on 3D digital image correlation

We have investigated the damage evolution and crack propagation of tuff rocks under axially cyclic tension–compression (T–C) loading with different amplitudes. The field of axial strains in the rock surface was obtained by three-dimensional digital image correlation (3D-DIC) method. The apparent strains were used to analyze the damage evolution along with the nucleation and propagation of microcracks until rock failure. The experimental results demonstrated that a local damage zone (LDZ) was formed when the loading amplitude exceeded a certain value, and the rock sample was prone to tensile failure under T–C cyclic loading. Based on arrangement of the virtual extensometers on the field of axial strains, the axial stress–strain curves, maximum axial strain, secant moduli, and dissipated energy evolution were obtained as a function of cycle number. It was observed that the variations in these mechanical parameters and dissipated energy significantly increased in the T–C cycle test with the increase in the loading amplitude. Particularly, due to obvious accumulation of residual compressive strain during the first cycle, the maximum tension stress increased, secant modulus decreased, and the dissipated energy evidently increased under tension during the second cycle. Furthermore, the mechanical parameters and dissipated energy evolution as a function of cycle number inside and outside the LDZ under 80% amplitude confirmed that the deformation mainly occurred inside the LDZ and the energy mainly dissipated for the nucleation and propagation of tensile microcracks vertical to the loading direction inside the LDZ during rock failure process.

Fatigue Characteristics of Limestone under Triaxial Compression with Cyclic Loading

This paper presents an experimental investigation of the fatigue properties of limestone subjected to triaxial compression with axial cyclic loading. Tests were conducted on intact limestone samples with a loading frequency of 0.5 Hz and a confining pressure of 10 MPa. The test results show the following five points. (1) Under triaxial conditions, the axial and circumferential deformations at the failure point induced by cyclic loading are slightly larger than the corresponding deformations at the peak stress achieved by conventional compression tests. (2) The first level cyclic loading process has a strong influence on rock deformation in the primary phase during subsequent level cyclic loading. A smaller difference in stress amplitude between the two loading stress levels leads to less deformation during the latter. (3) Circumferential and volumetric changes are more sensitive to fatigue failure in terms of deformation and strain rate than axial changes. (4) The three phases of dissipated energy evolution are consistent with a sample’s deformation such that the energy dissipation characteristics reflect the fatigue damage evolution process. (5) A new damage formula is proposed that can concisely describe a rock’s zero-cycle damage and damage evolution.

The study of energy balance in metals under deformation and failure process

The real time temperature measurement coupled with analysis of loading history data allows us to carry out the study of energy balance in metals under deformation and failure. Two independent techniques for estimation of deformation and failure induced heat sources in loaded sample were proposed. The techniques are based on temperature data treatment and original heat flow detector. The dissipated energy evolution was studied under quasistatic loading of Ti–0.8Al–0.8Mn sample and under fatigue crack propagation. Two regimes of energy dissipation at crack tip during its propagation in Paris regime were shown. The experimental data about dissipated and store energy evolution were supported by 3D numerical simulation based on the original theoretical model.

Cyclic behaviour of interior beam–column joints reinforced with plain bars

SummaryThe seismic damages commonly observed on beam–column joints of old reinforced concrete structures, built with plain bars and without proper detailing, justifies the need to further study the behaviour of this type of structures. The response of these structures when loaded cyclically, as occurs during the earthquakes, is partially controlled by the bond properties between the reinforcing bars and the surrounding concrete. This paper presents the results of an experimental campaign of unidirectional cyclic tests carried out on six full‐scale beam–column joints built with plain bars. These joint specimens are representative of existing reinforced concrete structures, that is, built without adequate reinforcement detailing for seismic demands. For comparison, an additional specimen is built with deformed bars and tested. The seven specimens are designed and detailed to allow the investigation of the influence of bond properties, lapping of the longitudinal bars in columns and beams, bent‐up bars in the beams, slab contribution and concrete strength. The lateral force–drift relationships, global dissipated energy evolution, contribution of the joint, beams and columns to the global dissipated energy, ductility, equivalent damping, final damage observed, homogenized reinforced concrete damage index, displacement components, curvature evolutions and Eurocode requirements are presented and discussed. Copyright © 2014 John Wiley & Sons, Ltd.

Energy Based Laboratory Fatigue Failure Criteria for Asphalt Materials

Abstract The definition of fatigue failure in the laboratory is not only an important but also a controversial issue. Researchers have developed a number of fatigue failure criteria, including the most traditional one, which defines failure at the cycle to 50 % initial modulus reduction. However, this definition is always challenged due to its lack of physical background. Recent studies showed that the dissipated energy ratio approach appears to be a favorable concept, which takes into account the fundamental dissipated energy evolution behavior of asphalt materials during a cyclic fatigue test. This paper conducted a review of three different energy based fatigue failure criteria and evaluated their applicability for fatigue data from asphalt binders and mixtures and under both stress and strain controlled loading modes. A macroscopic failure criterion is recommended, which is defined as the sudden change of the dissipated energy evolution curve and is consistently related to the beginning of macrocrack propagation. In addition, by comparing different failure criteria, the traditional 50 % initial modulus reduction criterion was found to have a strong correlation with energy based macroscopic fatigue failure for both mixtures and binders. It is thus suggested that the 50 % initial modulus reduction failure can be used as a simple but reasonable fatigue criterion, which indicates the transition from microcrack to macrocrack.