Thermo-Mechanical Damage in Porous Rocks: Theoretical Framework and Modeling Considerations

A coupled thermo-mechanical damage model for granite

The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program “Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing” are reviewed in this work. Large centrifugal compressor impeller blanks were used as the study object. The materials of the blanks were FV520B and KMN. The mechanism and evaluation model of ultra-high cycle fatigue, erosion wear, and corrosion damage were studied via theoretical calculation, finite element simulation, and experimentation. For ultra-high cycle fatigue damage, the characteristics of ultra-high cycle fatigue of the impeller material were clarified, and prediction models of ultra-high cycle fatigue strength were established. A residual life evaluation technique based on the “β-HV-N” (where β was the nonlinear parameter, HV was the Vickers hardness, and N was the fatigue life) double criterion method was proposed. For erosion wear, the flow field of gas-solid two-phase flow inside the impeller was simulated, and the erosion wear law was clarified. Two models for erosion rate and erosion depth calculation were established. For corrosion damage, the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated. KISCC (critical stress intensity factor) and da/dt (crack growth rate, where a is the total crack length and t is time) varied with H2S concentration and temperature, and their variation laws were revealed. Through this research, the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multistrength field and cross-scale were solved. The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.

Cutting tools are used in medicine a long time ago. Varying mechanical and thermal damage to bone tissue results from using cutting tools. These are often commented in the literature, but there is hardly any systematic studies of optimization of cutting tools. This present study was initiated in an attempt to improve the drill bit geometry and machining conditions. The study includes the thermal damage of bone and the soft-tissue injury, especially beyond the bone, by drilling of bone. The result of this study is a new drill bit geometry, which reduces the time of drilling. Thus lower temperature rises and less danger of thermal damage are achieved. It is easy to center and to start the cut with this new drill. The physical effort of the surgeon is substantially lessened. The danger of the soft-tissue injury can be disregarded. Optimized practice in medicine is gained by avoiding thermal and mechanical damage.

Meso- and micro-scale modeling of damage in plain weave composites

It is important to consider the closure of cracks and pores in rock for radioactive waste disposal and carbon capture and storage to maintain or decrease the permeability of rock. In this study, we investigated the precipitation of calcium compounds on the rock surface in calcium hydroxide solution to consider whether sealing of pores and cracks is possible and accelerated or not. It was found that the precipitation of calcium compounds occurred on rock surfaces. Additionally, we found that the closure of cracks and pores in rock occurred from the P-wave velocity measurement and observation by the scanning electron microscope. Since the closure of cracks and pores can decrease the permeability in rock, it is concluded that the precipitation of calcium compounds on rock is useful for the geological disposal of radioactive wastes and carbon capture and storage.

This paper presents the state of the art of the theory of rock damage and healing mechanics, with a particular emphasis on the strategies available to relate the micro-scale of crystals, cracks and pores to the scale of a Representative Elementary Volume (REV). We focus on mechanical degradation and recovery of stiffness and strength. Damage and healing models formulated in the author’s group are used as examples to illustrate and compare the reviewed micro-macro approaches, which include fabric enrichment, micromechanical formulations and homogenization schemes. This manuscript was written for doctoral students or researchers relatively new to the field of damage mechanics of geomaterials. Equations are provided to explain how to formulate a thermodynamically consistent model from scratch. Reviewing damage and healing modeling strategies led to the following conclusions: (i) The framework of hyperplasticity, which does not require any postulate on the existence or uniqueness of yield functions and which automatically ensures thermodynamic consistency, was never applied to Continuum Damage Mechanics (CDM). There may be an avenue to improve state-of-the-art damage and healing models in a similar framework of “hyper-damage mechanics”. (ii) In damage softening models, the mesh dependence of the width of the damage localization zone is currently alleviated by non-local regularization. Perhaps the next step is to couple micro-macro damage and healing models at the REV scale to discrete fracture mechanics at a larger scale to understand how damage and healing localization occurs. (iii) There may be an opportunity to use fabric-enriched models to capture the effect of microstructure organization on both mechanical properties and permeability. (iv) Coupling chemo-mechanical damage and healing processes across the scales would be useful to model the competition between damagre and healing whenever both can occur at the same temperature and pressure conditions. (v) Many challenges still exist to implement healing models in the Finite Element Method, especially in regards to the mapping of net damage.

On the coupling of anisotropic damage and plasticity models for ductile materials

To ensure personal safety and improve treatment efficiency in laser medical applications, one of the most important issues is to understand and accurately assess laser-induced thermal damage to biological tissues. Biological tissues generally consist of nonhomogeneous inner structures, in which heat flux equilibrates to the imposed temperature gradient via a thermal relaxation mechanism which cannot be explained by the traditional parabolic heat conduction model based on Fourier’s law. In this article, two non-Fourier heat conduction models, hyperbolic thermal wave model and dual-phase-lag (DPL) model, are formulated to describe the heat transfer in living biological tissues with blood perfusion and metabolic heat generation. It is shown that the non-Fourier bioheat conduction models could predict significantly different temperature and thermal damage in tissues from the traditional parabolic model. It is also found that the DPL bioheat conduction equations can be reduced to the Fourier heat conduction equations only if both phase lag times of the temperature gradient (τT) and the heat flux (τq) are zero. Effects of laser parameters and blood perfusion on the thermal damage simulated in tissues are also studied. The result shows that the overall effects of the blood flow on the thermal response and damage are similar to those of the time delay τT. The two-dimensional numerical results indicate that for a local heating with the heated spot being smaller than the tissue bulk, the variations of the non-uniform distributions of temperature suggest that the multi-dimensional effects of thermal wave and diffusion not be negligible.

Analysis of thermo-mechanical damage around tunnel and deposition boreholes of an underground nuclear waste disposal facility at the Forsmark site (Sweden) by 3D coupled FDEM simulations

Due to their strong absorption in water IR-lasers are excellent sources for precision cutting with minimal thermal damage in various fields of medicine. To understand the laser tissue interaction process one has to take into account the liquefaction of target material at the region of radiation impact. The dynamics of the created liquid may cause unexpected and undesirable effects for surgical laser applications. We studied the thermal damage along the walls of incision craters in terms of the elastic material properties and the dynamics of the drilling process. We show that the extension of thermally altered tissue is strongly influenced by the amount of hot liquefied tissue material remaining in the crater. When drilling into mechanically homogeneous materials this amount is essentially determined by the laser intensity used. However, when drilling through a composite structure consisting of various tissue types with different material properties, this is no longer the case. Even at low intensities, the damage zone varies substantially between the different layers. In our investigations we compared histologically and ultrastructurally the instantaneously created damage in the connective tissue and the subjacent skeletal muscle of skin after laser cutting, with long-time heating injuries. This comparison allows a differentiation between thermal and mechanical damage and an estimation of the minimum temperature created in the crater during the laser impact. The light microscopical examinations shows that the thermal damage in the connective tissue is about three times smaller than in the subjacent muscle layer. Comparative studies made with a composite structure consisting of the tissue substitutes gelatin and agar reveal that the unexpectedly large damage in the skeletal muscle layer is a result of the abrupt change of the elastic properties at the material transition. This discontinuity changes the ejection dynamics leading to a confinement of hot liquefied tissue material. The trapped hot liquid acts as an efficient heat source observed in the large damage of the muscle layer.

A recently developed anisotropic model of continuum damage mechanics has been applied successfully to characterize ductile fracture of cracked plates under mode I and mixed mode failures. The damage model is further extended in this investigation to examine its applicability to include notch ductile fracture of thin plates containing a circular hole. Two hole sizes of 16 mm and 24 mm diameters are chosen and the specimen material is aluminum alloy 2024-T3. Fracture loads of the plates are predicted by the damage model and compared satisfactorily with those determined experimentally. This investigation provides an important confirmation that not only the anisotropic model of continuum damage mechanics but also the same failure criterion developed can be effectively employed to characterize both ductile fracture for plates containing an isolated macro-crack or circular hole which would otherwise not be possible using the conventional theory of fracture mechanics. The successful development of the unified approach to characterize ductile failure provides a vital impetus for design engineers in the general application of the theory of continuum damage mechanics to solve practical engineering problems.

We have analyzed evaporation in high-level waste emplacement boreholes in unsaturated rock. Water dripping onto waste containers is assumed to spread and form a thin film on the container surface. Evaporation will occur due to decay heat and the difference in vapor pressure between water in a flat film and water held in rock pores with curved interfaces. They study evaporation in still air in the one-dimensional system shown in Figure 1. {delta} is the liquid film thickness and L + {delta} is the gap width. They assume motionless liquid-gas interfaces, ideal gases, constant total gas pressure, no gravitational effects, and local thermodynamic equilibrium between water liquid and vapor. Vapor pressure on the water film is described by Clapeyron equation. Vapor pressure in rock pores is described by Kelvin and Clapeyron equations. They solve the coupled energy conduction in liquid and vapor. Vapor pressure on the water film is described by Clapeyron equation. Vapor pressure in rock pores is described by Kelvin and Clapeyron equations. They solve the coupled energy (conduction in liquid and conduction and convection in gas) and mass (vapor-air binary diffusion) transport equations for quasi steady state to obtain the evaporative flux as a function of time.

Mechanical properties and damage model of modified recycled concrete under freeze-thaw cycles

Thermodynamic-based cohesive zone healing model for self-healing materials

Using ultrasonic investigations to develop anisotropic damage models for initially transverse isotropic materials undergoing damage to remain transverse isotropic