Thermal Damage Evolution Research Articles

Fracture Mode and Thermal Damage Evolution of Sandstone Under the Coupling Effect of Thermal Treatment and Impact Load

The dynamic properties of high-temperature sandstone quickly deteriorate with different cooling methods, which leads to the instability of underground engineering rock structures. Therefore, it is of great significance to quantify the changes in the dynamic characteristics of high-temperature cooled sandstone under impact loads. Therefore, the sandstone is heated to different temperatures and cooled using three methods. A dynamic tensile test is performed using the Splitting Hopkinson Pressure Bar (SHPB) test set for high-temperature cooled sandstone. At the same time, the transient process of rock failure was examined using high-speed cameras. The influence of different temperatures and cooling methods on the thermal damage value of sandstone was analyzed, and the prediction equation was formed. The change in rock energy during rock failure under impact load was calculated.

Microscopic mechanism analysis of temperature influence on rock salt and thermal damage evolution of surrounding wall in underground salt cavern

Microscopic mechanism analysis of temperature influence on rock salt and thermal damage evolution of surrounding wall in underground salt cavern

Study on the influence of temperature on the damage evolution of hot dry rock in the development of geothermal resources

In order to more accurately understand the rock mechanics properties of hot dry rock (HDR) reservoirs under high-temperature conditions and further guide the drilling and construction of HDR wells, conducting research on rock damage evolution under high-temperature conditions plays a guiding role in the efficient development of geothermal resources. To reveal the evolution law of fracture damage of HDR under temperature influence, taking marble as an example, the thermo-mechanical damage and failure mechanism under the conditions of 30 °C, 60 °C, 90 °C, 120 °C and 150 °C were studied using a rock high-temperature rheometer and an acoustic emission (AE) testing system. The numerical simulation results were compared with the indoor experimental results by combining the particulate flow program Particle Flow Code 3D (PFC3D) to verify the effectiveness of the simulation analysis model of thermo-coupled particulate flow at the micro scale. The results show that under high temperature, the marble three-axis compression failure passes through the compaction and elastic deformation stage, plastic deformation stage, ductile failure stage and instability failure stage, and the peak strength and elastic modulus of the marble decrease with the increase of temperature, and the acoustic emission b-value of the sample can judge the damage evolution process of the marble. At the micro scale, high temperature accelerates the force chain transmission between particles, the contact force between marble particles gradually decreases during the heating process, and the number of particle bonding failures increases steadily; the bearing capacity and elastic modulus attenuation of the rock are the result of microcrack evolution, and the force chain void zone and particle displacement field inside the sample are consistent with its macroscopic failure form. The development of microcracks in marble under different test loading conditions is different, and with the increase of test temperature, the total number of cracks inside the sample increases, but the proportion of shear cracks decreases, the activity of particle displacement increases, and the “plastic extension” characteristic of marble becomes more significant. The thermal damage evolution of marble was quantitatively analyzed based on the elastic modulus method and the peak stress method, and the damage evolution law of marble under different temperatures was obtained.

Thermal damage evolution of granite under different thermal conditions based on two-scale tessellation via discrete element method

This paper presents a numerical modeling method that integrates a grain-growth model and Voronoi polygon configuration to investigate the thermal damage characteristics and fracture mechanism of granite under three distinct thermal conditions: rapid heating, slow heating, and cycle heating. The proposed method accurately simulates the intra-grain damage modes of mineral particles and the mechanical responses of granite. Through the simulation, it was observed that slow heating induces more significant deterioration compared to rapid heating, while cycle heating leads to wider crack openings and apparent brittle damage during the cooling phase. Furthermore, the peak strength and elastic modulus of granite demonstrate a significant decrease with increasing temperature under all three heating conditions. Notably, slow heating exhibits ductility characteristics in its post-peak residual strength. This study also analyzes the effects of different thermal conditions on the damage evolution pattern and cracking mechanism of rocks. It is found that slow heating generates a higher number of cracks with a broader distribution and intra-grain damage, whereas cycle heating results in severe cracks and fractures. The findings of this study have practical implications for preventing and controlling thermal disasters in deep rock engineering.

A thermo-mechanical coupling model for concrete including damage evolution

In the current study, a coupled thermo-mechanical constitutive model of concrete was newly developed to characterize the mechanical responses of concrete at different temperatures within thermodynamics framework. The coupling thermo-mechanical contributions among thermal effect (up to 800°C), damage evolution and thermo-plastic hardening were creatively taken into account in energy potential function. The thermal damage evolution law and load induced plastic mechanical damage evolution law was developed respectively and were coupled in the dissipation function. The thermo-mechanical hardening rule was considered through adopting back stress and hardening parameters. A particular advantage of the proposed model is that fiber influence coefficients can be employed in potential functions to upgrade for modeling fiber reinforced concrete. The impact of types and volume fractions of fibers on the reinforcement mechanism was calculated in the fiber influence coefficients. Besides, an orthotropic triaxial compression model was developed for concrete and fiber reinforced concrete to predict multiaxial stress behavior at high temperature. The proposed model was coded and implemented into the Fortran program and the nonlinear behaviors of concrete and fiber reinforced concrete were predicted. Good effectiveness and accuracy have been validated through comparing the modelling results and six groups experimental results in literatures, which illustrates that the proposed model is robust and reliable. Finally, a discussed study was conducted to investigate the effect of hardening parameters and thermal effect on the yield surface.

Effects of thermal damage on natural gas transport capacity of tight sandstone after electrical heating

As an environment-friendly method, downhole electric heating can cause thermal damage to the rock around the well, so as to improve the gas transport capacity of tight sandstone gas reservoir (TGR), but its mechanisms are not well established. In the present study, a comprehensive analysis of the thermal damage characteristics of tight sandstones has been conducted, employing a suite of microscopic investigative techniques such as differential thermal gravimetry, X-ray diffraction, and scanning electron microscopy. The experimental results were related to permeability test results and then combined with constant-pressure heating acoustic rock tests. Subsequently, the heating and cooling processes along with the effects of confining pressure on the damage evolution and gas transport capacity were analysed. According to the difference in thermal damage mechanism, three temperature ranges were identified: 100–300 °C, 300–1000 °C, and 1000–1200 °C. In the first stage, free water escaped, clay minerals expanded, and a small number of weak cementation cracked, resulting in a 26.18% decrease (200 °C) and a 56.95% increase (300 °C) in permeability. In the second stage, the clay minerals were stripped of their bound water; with an increase in temperature, heat-induced cracks were initiated, propagated, and aggregated to form a network. The permeability increased exponentially by 938-fold. Finally, in the third stage, with the initiation of feldspar melting, the mineral surface was smooth; furthermore, permeability increased rapidly by 164.08%, after which the pores were blocked rapidly. Acoustic tests under constant-pressure heating conditions showed that thermal damage continued to evolve during the cooling phase because of the temperature variable stress. External pressures could only partially limit the evolution of thermal damage. The findings of this study illustrate that downhole electric heating (300–1000 °C) can improve natural gas transport capacity by eliminating water phase trap damage and creating a multi-scale crack network in a near-wellbore area. In addition, the nonlinear evolution of permeability in tight sandstones is different from that in other rocks, and the S-wave attenuation coefficient can well characterise this phenomenon. Thus, a mathematical model of nonlinear permeability evolution based on the principle of dual percolation is derived. Therefore, the results of this research provide a reference for the temperature selection and acoustic monitoring of the TGR downhole heating process.

Interfacial thermal damage and fatigue between auxetic honeycomb sandwich and underneath substrate

A general model to evaluate the interfacial thermal damage and predict the fatigue life of the auxetic honeycomb-substrate structure (H-SS) is built. To improve the accuracy, all material parameters in the model are temperature-dependent. The transient temperature field and the associated thermal stresses associated with the temperature changes in the structure are determined by the finite difference method. The interfacial thermal stress intensity factor is employed to characterize the stress concentration behavior. Based on the stress field and the stress concentrations at the interface, interfacial thermal damage evolution and fatigue life prediction of the structure are made. The results show that the auxetic property can significantly enhance the fatigue life of the structure. The fatigue life will be undervalued when the effect of temperature-dependent material properties (TDMPs) is neglected. Furthermore, the influence of TDMPs on the fatigue life of the structure will increase as the absolute value of the internal cell angle increases. This paper provides a comprehensive assessment of the thermal damage and fatigue life of auxetic H-SSs and can serve as a solid theoretical foundation for future applications of related structures in extreme temperature environments.

Salt Cavern Thermal Damage Evolution Investigation Based on a Hybrid Continuum-Discrete Coupled Modeling

The integrity and stability of salt caverns for natural gas storage are subjected to a gas cycling loading operation. The coupled effect of confining pressure and temperature on the response of the salt cavity surrounding the wall is essential to stability analysis. In this study, a hybrid continuum-discrete model accounting for the thermal-mechanical process is proposed to investigate the thermal-damage evolution mechanism towards a field case with blocks falling off the salt cavity. The salt cavity is modeled by continuum zones, and the potential damage zones are simulated by discrete particles. Three specimens at different locations around the surrounding wall are compared in the context of severe depressurization. The dynamic responses of rock salt, including temperature spatiotemporal variation, microscopic cracking patterns, and energy evolution exhibit spatial and confinement dependence. A series of numerical simulations were conducted to study the influence of microproperties and thermal properties. It is shown that the evolution of cracks is controlled by (1) the thermal-mechanical process (i.e., depressurization and retention at low pressure) and (2) the anomalous zone close to the brim of the salt cavity surrounding the wall. The zone far away from the marginal surrounding wall is less affected by temperature, and only the mechanical conditions control the development of cracks. This continuum/discontinuum approach provides an alternative method to investigate the progressive thermal damage and its microscopic mechanism.

Variable porosity-based bioheat model vs variable perfusion-based Pennes’ equation: A comparison with in vivo experimental data

• Variable porosity and variable perfusion based bioheat models developed. • Modelling in vivo thermal ablation of a tumor liver tissue bounded by healthy tissue. • Comparison between Pennes’ equation and porous media-based model. • Results in terms of temperature fields and final ablation zones diameters. • Accurate prediction of ablation zones to improve both medical protocols and devices. Thermal ablation has a primary role in cancer treatment due to its minimal invasiveness, and the improvement of this technique is fundamental in order to avoid incomplete ablation or healthy tissues ablation. In this work, modified bioheat models based on Pennes’ or LTNE bioheat models are employed in a simplified two-layer spherical model made up by a hepatocarcinoma tumor bounded by a healthy liver tissue. Improvements are done by including variable porosity or perfusion into either LTNE-based or Pennes-based models, accounting for local properties variations. Other modifications in common to both models, like blood flow arrest induced by necrosis, or employing an equivalent external thermal dose as the heat source term, are introduced too. Numerical results are presented in terms of temperature fields, thermal damage evolution, and the resulting ablation size. The latter, that represent the main outcome from a thermal ablation procedure, is compared with experimental measurements performed on an in vivo clinical study referred to hepatocellular carcinomas in human beings. From these comparisons, it is shown that the modified porous media-based model provides a very good agreement, with lesion sizes differences which are no higher than 9.1%; on the other hand, the modified Pennes’ equation allows to a slight underestimation of the achieved temperatures due to a too much high heat sink effect. The information derived from the present study would be very helpful to improve thermal ablation modeling by employing a LTNE bioheat porous model that accounts for aspects like variable porosity and other model improvements.

Amplitude-Modulation Vibro-Acoustic Technique for Damage Evaluation

This study proposes an amplitude-modulation vibro-acoustic (AMVA) technique to track the evolution of thermal damage in pristine graphene mortar. In the proposed amplitude-modulation technique, the pump wave is amplitude-modulated using three different methods: (1) the pure amplitude-modulated (PAM) method, (2) the suppressive amplitude-modulated (SAM) method and (3) the transmitted amplitude-modulated (TAM) method. The nonlinear parameters , and corresponding to the PAM, SAM and TAM methods, respectively, are theoretically established and experimentally demonstrated that the nonlinear parameters associated with the material nonlinearity, and they can be used to quantitatively characterize different damage stages of thermal damage. Meanwhile, the resonant frequency (RF) and ultrasonic pulse velocity (UPV) tests are conducted. The linear measurements, dynamic elastic modulus obtained from RF test and ultrasonic pulse velocity collected by UPV test, are used to compare with the nonlinear parameters. The results show that the proposed AMVA technique is more sensitive and feasible to serve as the tool for thermal damage detection in cement-based material compared with the conventional RF and UPV techniques.

Study on the mechanical characteristics and damage evaluation of concrete-rock combination after high temperatures exposure

Concrete-rock combination (CRC) plays an important role in ensuring the safety and stability of the engineering (such as geothermal exploration, the production well, and radioactive waste storage) under high-temperature mechanical coupling conditions. In this study, a mechanical testing machine and an acoustic emission system were applied to investigate the mechanical properties of CRC after treatment at different temperatures (25 °C, 100 °C, 300 °C, 500 °C and 700 °C). A new theoretical model was established to study the thermal damage evolution. Meanwhile, the experimental results demonstrate that the peak strength of CRC is 36.6% for rock, and the peak strength of CRC is 129.6% relative to the concrete. When the temperature ranges from 25 °C to 500 °C, the stiffness decreases slowly, but above 500 °C, the stiffness decreases significantly. Additionally, the AE monitoring can well capture the damage location and microcrack process of CRC during the mechanical loading process after exposure to high temperatures. Finally, the theoretical values of the damage constitutive model are consistent with the experimental data, which verifies the validity of the damage model. Our new findings contribute to a better experimental and theoretical basis for CRC using complex environmental engineering.

Investigation of thermal-mechanical effects on salt cavern during cycling loading

Traditional stability analysis for salt cavern as UGS overlooks the thermal effects induced by cycling loading and cannot predict the potential risk. In this study viscoelastic WIPP model is employed to describe the temperature-dependent creep behavior of rock salt. A thermal-mechanical simulation framework is established to couple the effect of mechanical stress and thermal stress. A coupling thermal-mechanical numerical model implemented by FLAC3D in combination with the WIPP creep model is proposed. A field case, Cavern L, in Jintan, Jiangsu Province of China is demonstrated in this paper to explore the thermal response to gas injection-and-withdrawal process. The results show that there is tensile stress concentration region at the cavern roof. The dynamic process of thermal damage evolution and block falls on cavern roof is also investigated. The disintegration of rock salt mass at cavern roof occurs after the most severe gas depressurization period, and the retain of low pressure after gas withdrawal aggravate the thermal damage. It indicates that the thermal-induced tensile stresses are critical for salt cavern stability assessment. The feasibility and accuracy of the proposed thermal-mechanical modeling is verified by the field case, and the simulation results of thermal damage are coincided with the sonar results. This analysis confirmed the influence of thermal-mechanical effects on salt cavern wall. The approach used in this study provides an improved method for the stability evaluation and optimal operation parameters for salt caverns.

A novel true triaxial test system for microwave-induced fracturing of hard rocks

This study introduces a test system for microwave-induced fracturing of hard rocks under true triaxial stress. The test system comprises a true triaxial stress loading system, an open-ended microwave-induced fracturing system, a data acquisition system, an acoustic emission (AE) monitoring system, and an auxiliary specimen loading system. Microwave-induced surface and borehole fracturing tests under true triaxial stress were fulfilled for the first time, which overcomes the problem of microwave leakage in the coupling loading of true triaxial stress and microwave. By developing the dynamic monitoring system, the thermal response and fracture evolution were obtained during microwave irradiation. The monitoring system includes the infrared thermometry technique for monitoring rock surface temperature, the distributed optic fiber sensing technique for monitoring temperature in borehole in rock, the AE technique and two-dimensional digital speckle correlation technique for monitoring the evolution of thermal damage and the rock fracturing process. To validate the advantages of the test system and investigate the characteristics of microwave-induced fracturing of hard rocks, the study demonstrates the experimental methods and results for microwave-induced surface and borehole fracturing under true triaxial stress. The results show that thermal cracking presented intermittent characteristics (calm–active–calm) during microwave-induced surface and borehole fracturing of basalt. In addition, true triaxial stress can inhibit the development and distribution of thermal cracks during microwave-induced surface fracturing. When microwave-induced borehole fracturing occurs, it promotes the distribution of thermal cracks in rock, but inhibits the width of cracks. The results also prove the reliability of the test system.

Influences of thermal damage on water transport in heat-treated cement mortar: Experimental and theoretical analyses

Water transport in the heat-damaged cement mortar is closely related to the evaluation of durability for structures exposed to fire and the recycling of thermally damaged cement-based materials. In this study, the influence of microstructure on water transport in unsaturated and saturated heat-treated cement mortar was analyzed based on experimental results from neutron radiography, water permeability, mercury intrusion porosimetry (MIP) and X-ray computed tomography (CT) tests. Neutron radiography was employed to track the dynamic wetting front in real time during water imbibition in the heat-treated mortar specimens exposed to a series of temperatures (105°C, 200°C, 400°C, 600°C, 800°C). The evolution of the wetting front was analyzed according to the square root of time based on neutron images. A deviation from the standard t1/2 pattern of the wetting front was found when water imbibition in the cement mortar specimens treated by a temperature ≥400°C. The absorptivities of different imbibition stages were determined for heat-damaged cement mortar. Mechanisms for the change of typical absorptivities with the evolution of thermal damage were discussed from the perspective of microstructure. In addition, causes for the occurrence of anomalous water absorption were explored by considering the role of thermal cracks and potential physicochemical reactions. Methods were proposed to estimate the effective tortuosity of water channels in the cement mortar damaged by different temperatures. The representative size of water channels was estimated with the calculated tortuosity. The estimated water channels size was compared with the pore aperture determined by MIP. At last, the estimated water channels size and tortuosity from imbibition data were utilized to predict the water permeability of the heat-treated mortar using a capillary model. By comparing the predicted and measured permeabilities, the correlation and difference between unsaturated and saturated water transport in the heat-treated cement mortar were analysed. Future work for modeling water transport in heat-damaged cement mortar was discussed.

Experimental and numerical analysis of damage mechanisms for carbon fiber-reinforced polymer composites subjected to lightning strikes

This study aims to reveal the damage properties and mechanism of carbon fiber-reinforced polymer (CFRP) composites subjected to lightning current component A by artificial lightning tests and simulation analysis. The lightning strike process was observed by using a high-speed camera and infrared temperature measurements. The surface damage and internal damage were inspected via ultrasonic and 3D X-ray scanning. The damage behavior of CFRP composite was deduced and the damage regions were quantitively analyzed by detecting the surface morphology and microstructural changes and analyzing the lightning strike process. The results indicated that the lightning-induced damage included lightning attachment damage due to direct contact with the lightning arc, laminate peeled-off damage caused by the explosive gas impact, and internal delamination induced by expanding pyrolysis gas. A coupled thermal-electric CFRP model, which first introduces the dynamic conductivity of CFRP materials, was established. The comparison results indicated that the Joule heating-based numerical model can simulate the evolution of thermal damage well, although the laminate peeled-off damage resulting from the mechanical impact was not included in the simulation scope. A temperature field criterion and a pyrolysis degree field criterion were proposed and verified for evaluating in-plane and in-depth damage with acceptable deviations.

Acoustic emission uncovers thermal damage evolution of rock

The thermal damage evolution of rock closely relates to many important scientific and engineering problems, such as the mechanisms of earthquake and the effective extraction of deep geothermal energy. However, there is lack of rational thermal damage evolution model, and the mechanisms of thermal damage are still unclear especially during cooling. By use of a specially designed acoustic emission (AE) test system, we explored the thermal damage evaluation in a rock and established a thermal damage evolution model which takes into account both heating and cooling processes. The mechanisms of rock damage caused by heating and cooling were analyzed by using a lattice spring model, and two different microstructural explanations were found, i.e. heterogeneous microstructure and microdefect structure. The damage evolution model can be used for more accurate modeling of these problems which involve rock thermal damage, such as induced seismic activity during deep geothermal exploration.

Thermal damage evolution of granite under slow and high-speed heating conditions

Abstract A continuum based numerical approach is used to investigate the effects of slow and high-speed heating, including the ISO 834 fire curve, on thermal cracking of granite. During slow heating, thermal stress variations are mainly controlled by the heterogeneous thermal expansion of mineral grains. As a result, the stress concentrations are more isolated and dispersedly distributed throughout the sample. High-speed heating produces large thermal gradients especially at the outer surface of the samples, inducing big thermal strain increments and subsequent high compressive stresses. Larger cracks are formed due to a wider range of concentrated tensile stresses inside the sample during high-speed heating. At low temperatures, slow heating has a stronger influcence on micro-cracking. Due to larger cracks and newly induced micro-cracks, high-speed heating has an increasingly important impact on crack pattern in granite at high temperatures. Although shear failures show a significant increase at 800 °C, tensile cracks are still the majority of total failures in both, slow and high-speed heating scenarios. The final crack pattern in granite under fire conditions is a result of different cracking behaviors caused by various heating rates. This consequently affects strength and final failure pattern of granite.

Gas Transport in the Insensitive High Explosive PBX 9502

AbstractSmall‐scale laboratory experiments were performed to analyze gas transport mechanics in PBX 9502, an insensitive high explosive (IHE) composition. Two independent investigations are reported here. First, gas permeametry and dynamic pycnometry techniques were used to measure the molecular flow (Knudsen) coefficient and the internally interconnected void fraction of pristine and thermally damaged samples in two uniaxial pressing orientations. The permeability of PBX 9502 was found to be unmeasurably low (of the same order of magnitude as PTFE) with gas transport being diffusion‐dominated. Secondly, a pressure vessel experiment was developed to measure quasi‐static and dynamic gas generation as the explosive was heated to self‐ignition (cookoff). The gas generation results and the permeability/diffusivity findings provide evidence that PBX 9502 remains impermeable until seconds prior to self‐ignition. At ignition, internal void‐pressure drives macro‐scale cracking and the sample becomes uniformly incorporated in the following deconsolidating deflagration. These results are discussed within the context of previous observations of pressure‐dependent cookoff behavior of PBX 9502 and provide a more complete description of thermal damage evolution in this explosive composition.

Monitoring of Thermal Damage Evolution in Concrete Parts by Acoustic NDT Methods

The paper presents the results of the experimental work which was focused on the use of the Impact-echo method for testing of concrete specimens damaged by high-temperature. The test specimens were heated to 600 and 800 °C for sixty, one hundred twenty and three hundred minutes. After heating, the samples were continuously cooled to room temperature and tested by Impact-echo method.

On the thermal forming limit diagram (TFLD) with GTN mesoscopic damage model for AA7075 aluminum alloy: Numerical and experimental investigation

The formability of high strength AA7075 aluminum alloy under elevated temperatures is vital in guiding the fabrication of automobile structural parts. The ductile fracture forming limit of AA7075 at elevated temperatures is essentially governed by thermal damage evolution. In this paper, the hot tensile test (300ºC-450 °C, strain rate 0.1s−1-0.001s−1) for AA7075 was conducted and the corresponding flow behavior was fitted by Hensiel-Spittel (HS) constitutive equation. The GTN mesoscopic damage model was implemented to take account of the damage evolution phenomenon of AA7075 at elevated temperatures. The temperature-dependent damage void volume fractions (VVF) were identified accurately based on a novel inverse identification procedure, named the CCD parameters design-FEM inverse simulation-genetic algorithm (CCD-FEIS-GA) optimization method. Subsequently, the thermal forming limit diagram (TFLD) was calculated based on the GTN damage parameters and further validated by hot Nakajima-type bulging experiment. The corresponding damage evolution behaviors and effects of critical forming parameters were discussed in detail. The comparison of experimental and numerical results showed that the formability of AA7075 firstly increases and then decreases with the increasing forming temperature, the TFLD0 reaches its maximum value when the temperature is 400 °C, and the formability also increases with the increasing strain rate and the decreasing surface coefficient of friction. The proposed simulated strategy coupled with mesoscopic GTN approach conduces to the accurate prediction of TFLD and damage fracture behavior of AA7075 in the hot forming process.