Thermal Crack Growth Research Articles

Frictional Wear and Thermal Fatigue Properties of Die Steel after Ultrasound-Assisted Alloying

The surface layer of 8407 die steel was strengthened using the combination of ultrasonic surface rolling and high-energy ion implanting in the present work. The strengthened layer was then characterized via microstructure observation, composition analysis, and hardness test. After that, the frictional wear and thermal fatigue properties of high-energy ion implanting specimens and composite-reinforced specimens were compared. Results show that the pretreatment of specimens with ultrasonic surface rolling causes grain refinement in the material surface, which promotes the strengthening effect of high-energy ion implanting. The wear volume of composite-reinforced specimens at medium and high frequencies is reduced by about 20%, and the wear resistance of these specimens is significantly improved with a lower friction coefficient and wear volume at moderate and high frequencies in alternating load friction experiments. Meanwhile, the thermal fatigue crack depth of composite-reinforced specimens is reduced by about 47.5%, which effectively prevents the growth of thermal cracks in the surface, thus improving the curing ability of the implanted elements. Therefore, composite strengthening of the mold steel surface is conducive to improving the cycle life, ensuring accuracy, effectively hindering the expansion of thermal cracks, and saving the cost of production.

Multiscale Theoretical Model of Thermal Conductivity of Concrete and the Mesoscale Simulation of Its Temperature Field

Temperature field analysis is the precondition of studying the heat and mass transfer and durability of a concrete building; thermal conductivity is a key parameter that affects the distribution of the temperature field of concrete. Through reasonable assumptions and simplifications, the relationship between the micro-microscopic composition of concrete and its macroscopic thermal conductivity is established, and a multiscale theoretical model of thermal conductivity considering the influence of interface transition zone (ITZ) is proposed. The model can predict the thermal conductivities of concrete and its components at an arbitrary saturation. Subsequently, the influence of saturation, water-cement ratio, volume fraction and type of coarse aggregate, and sand ratio is researched. Moreover, according to the prediction results of the proposed model, a mesoscale simulation of the concrete temperature field is carried out. The results demonstrate that the presence of aggregate and ITZ leads to the isotherm deflection and abruption at the junction of the phases. Meanwhile, the heat flux density at the corners of the polygonal aggregate is significantly higher than at other positions; the phenomenon, first named the “corner effect” in the research, causes the temperature field distribution of concrete containing polygonal aggregates to be more uneven than that of circular and elliptical aggregates, and it is more likely to produce temperature-induced cracks. The research helps explain the influence mechanism of material components on the thermal conductivity of concrete and the distribution of its temperature field and provides a basis for the fine simulation of concrete thermal crack growth and creep at variable temperatures.

Study on thermal fatigue behaviors of two kinds of vermicular graphite cast irons

Abstract Due to the good thermal stability and mechanical properties, vermicular graphite cast iron is widely used to make industry components. Many of them are inevitably impacted by alternating temperature load. Therefore, two kinds of vermicular graphite cast irons, RuT400 and RuT450, were employed to study the features of thermal fatigue crack initiation and propagation in different temperature ranges. And the relationship between the length of thermal fatigue crack and number of cycles were also analyzed. It can be found that the thermal fatigue properties between the two materials are obviously different because of different microstructures. At present testing temperatures, RuT450 has higher pearlite content, lower thermal crack growth rate, higher transition temperature. The grain boundary slide temperature of ferrite and transition temperature of pearlite have important influences on the thermal fatigue cracks of two kinds of vermicular graphite cast irons.

Effect of temperature on physical, mechanical and acoustic emission properties of Beishan granite, Gansu Province, China

The study of the influence of temperature on granite's physical and mechanical properties is significant to deep geotechnical engineering such as nuclear waste disposal engineering. The granite samples were taken from Beishan of Gansu Province, China, a candidate site for a high-level radioactive waste repository. In this paper, thermal damage on Beishan granite under different temperature (25 °C, 200 °C, 300 °C, 400 °C, and 500 °C) was studied to investigate the thermal effect on physical and mechanical properties. Uniaxial compression tests, ultrasonic velocity, acoustic emission (AE) monitorization and scanning electron microscope were adopted. The results showed that: (1) a temperature threshold of 300 °C was recognized, with the increasing temperature, the peak strength, P-wave velocity, and mass loss ratio of the granite decreased sharply. (2) combining with the scanning electron microscope results, the changes in the growth of thermal cracks due to the heating of granite at different elevated temperatures indicated the cracks in the rock increased and gradually formed a fractures zone eventually leading to rock failure. (3) The granite sample was a brittle splitting failure when the temperature was below 200 °C, the failure of granite sample presented shear failure once the temperature exceeded 200 °C (4) The accumulated AE counts increased when the stress reached $$\sigma_{ci}$$ (crack initiation stress) and increased significantly when the stress reached $$\sigma_{cd}$$ (crack damage stress). The higher the temperature was, the more seriously the granite samples were damaged.

Enhanced model for thermally induced transverse cracking of asphalt pavements

Thermal cracking is a non-load associated distress mode of asphalt pavements. Finite element models (FEM) were first introduced in this study to determine the thermally induced J-integral at the tip of thermal crack. After extensive runs of the FEM, artificial neural network models were constructed to predict the J-integral, which was used in the Paris’ law to calculate the cumulative thermal crack growth over time and thermal cracking fatigue life. Additionally, Long-term pavement performance data was collected to characterize the thermal cracking in different climatic zones. The calculated fatigue life was well correlated with the observed transverse cracking field performance.

Effect of high temperature on physical and mechanical properties of Jalore granite

Underground nuclear waste disposal is an important area of research which requires concepts related to thermal cracking in brittle rock. The disposed canister produces residual heat that results from the decay of radionuclide's; increase the heat in the surrounding rock.The changes of mineral composition and pore water content of the rock after heating lead to the variation of the physical and mechanical properties of the host rock.In this study, an experiment was carried out to study the thermal effect (from 25 °C to 600 °C) on stress-strain behavior, elastic modulus, peak stress, thermal damage, and tensile strength of Jalore granite, India and compared with similar properties of granite from other countries. Scanning electron microscope (SEM) analyses have been done to determine the changes in growth of thermal cracks due to heating of Jalore granite at different elevated temperature. Based on the temperature interval (between 25 °C and 600 °C) can be divided into two zones from 25 °C–300 °C to 300 °C–600 °C. It was observed that the compressive strength and tensile strength of rock increased as the temperature was gradually increased up to 300 °C, but decreased sharply above this temperature. In the temperature range of 300 °C–600 °C, stress-strain curves showed plasticity behavior in which brittle-ductile transition was observed. It was observed that thermally-inducedmicro-cracks because of its complexity in thermal expansivity, the densification stage is longer which increases the crack density rapidly, at the same time, the elastic modulus, compressive strength, and thermal damage are higher. Heating at high temperature will make the tensile strength of granite change due to the loss of water and minerals and the effect of thermal stress that the most conspicuous effect is the expansion of quartz.It is found that 300 °C is the critical temperature for Jalore granite above which the physicomechanical behavior reduces sharply. A very strong correlation was found between the compressive strength and tensile strength of Jalore granite rock with very high coefficients of determination.

Surface thermal shock fracture and thermal crack growth behavior of thin plates based on dual-phase-lag heat conduction

This paper studies the thermoelastic problem of a surface cracked plate subjected to a suddenly cooling under the framework of dual-phase-lag heat conduction model. The thermally induced stress intensity factor is calculated based on the linear theory of thermoelasticity. The results demonstrated that the non-Fourier effect is significant in very small time scale which is comparable to the thermal flux lag of the material. The thermal stress intensity factor increases with the thermal flux lag and temperature gradient lag of the material. In addition, the dual-phase-lag heat conduction model predicts a faster cracking behavior than the hyperbolic single-phase-lag heat conduction model and Fourier model in the beginning of thermal shock. It is also found that the crack growth terminates at a critical crack length, which increases with the temperature gradient lag of the material.

A coupled thermo-mechanical bond-based peridynamics for simulating thermal cracking in rocks

A coupled thermo-mechanical bond-based peridynamical (TM-BB-PD) method is developed to simulate thermal cracking processes in rocks. The coupled thermo-mechanical model consists of two parts. In the first part, temperature distribution of the system is modeled based on the heat conduction equation. In the second part, the mechanical deformation caused by temperature change is calculated to investigate thermal fracture problems. The multi-rate explicit time integration scheme is proposed to overcome the multi-scale time problem in coupled thermo-mechanical systems. Two benchmark examples, i.e., steady-state heat conduction and transient heat conduction with deformation problem, are performed to illustrate the correctness and accuracy of the proposed coupled numerical method in dealing with thermo-mechanical problems. Moreover, two kinds of numerical convergence for peridynamics, i.e., m- and $$\delta $$ -convergences, are tested. The thermal cracking behaviors in rocks are also investigated using the proposed coupled numerical method. The present numerical results are in good agreement with the previous numerical and experimental data. Effects of PD material point distributions and nonlocal ratios on thermal cracking patterns are also studied. It can be found from the numerical results that thermal crack growth paths do not increases with changes of PD material point spacing when the nonlocal ratio is larger than 4. The present numerical results also indicate that thermal crack growth paths are slightly affected by the arrangements of PD material points. Moreover, influences of thermal expansion coefficients and inhomogeneous properties on thermal cracking patterns are investigated, and the corresponding thermal fracture mechanism is analyzed in simulations. Finally, a LdB granite specimen with a borehole in the heated experiment is taken as an application example to examine applicability and usefulness of the proposed numerical method. Numerical results are in good agreement with the previous experimental and numerical results. Meanwhile, it can be found from the numerical results that the coupled TM-BB-PD has the capacity to capture phenomena of temperature jumps across cracks, which cannot be captured in the previous numerical simulations.

Effect of Vanadium on Thermal Fatigue Resistance of Cr5 Deposited Metal

In the present work, effect of vanadium on mechanical and thermal fatigue resistance of Cr5 deposited metal is investigated. It is found that hard phases with rich vanadium are mainly distributed at grain boundaries. Vanadium affects the high temperature tensile strength and thermal fatigue cracking obviously. With the increase of vanadium content, high temperature tensile strength of deposited metals shows a initial rise up, then drop for more than 0.54 wt.% V. Toughness and high temperature plasticity are increased up to 0.26 wt.% V, then drop up to 0.89 wt.% V, then toughness and plasticity increase again. Moreover, the thermal fatigue crack length shows a initial decrease up to 0.26 wt. % V, then slightly rise up for 0.89 wt.% V, then crack length shorten again. It is expected that the optimal vanadium content is in a range of 0.18~0.26 wt.% for resisting the thermal crack growth. Fractographic observation shows that the thermal fatigue cracks mainly are transgranular growth. It is felt that the crack length is closely related to microstructure, oxidation resistance, toughness and high temperature plasticity of the deposited alloy

ＷＣ含有Ｔｉ（Ｃ，Ｎ）基サーメットの微視組織が切削特性に及ぼす影響

Ti(C,N) base WC containing polygenic cermets possessing both wear resistance, toughness and characteristics gained from the fine surface perfect for products have been used in multiple ways in the milling process of SKD11 steel used as a metallic material in recent years. However thermal cracks form at the tip of the tool blade in milling process conditions where a severe intermittent load is repeated, often reducing the life of the tool. The life of the tool needs to be lengthened.This study investigated the effect of microstructure that changes according to the WC content amount in the cermet when SKD11 materials are intermittently processed using a WC containing Ti(C,N) base cermet tool on the milling cutting performance in order to develop a milling cutting process cermet tool. We also observed and rated signs of thermal cracks created on the tip of the tool blade using a transmission electron microscope(FE,TEM). This showed that cermet materials containing much WC in a range where abnormalities do not occur form triple dense core rigidity with a (Ti, W) C rim or double dense core rigidity with a (Ti, W) C core, and the lifespan of defect resistance is extended because the thermal crack growth resistance is increased.

Strain‐based approach to crack growth and thermal fatigue life of hot work tool steels

Thermal fatigue cracking is one of the most important life‐limiting tool failure mechanisms in die casting of aluminium and brass. It results from the rapid alternating heating and cooling of the die surface during the casting process, and it is observed as a network of fine cracks on the tool surfaces exposed to thermal cycling. The crack pattern deteriorates the surface finish of the tool and, therefore, that of the cast products. Hot work tool steels are frequently used as die materials to minimise this tool damage. In this study, thermal fatigue cracking of two hot work tool steel grades, hardened and tempered to various conditions, were evaluated using an experimental thermal fatigue test method based on cyclic induction heating and internal cooling of hollow cylindrical test rods. The surface strain is continuously recorded during the thermal cycling through a noncontact laser speckle technique. The thermal fatigue damage was characterised with respect to crack length and density of cracks. Based on the experimental findings estimations of crack growth and thermal fatigue life, and their temperature sensitivity were made. In addition, the crack growth and thermal fatigue life were represented using strain‐based models. It was found that the resistance against thermal cracking improves with initial tool steel hardness, in spite of the fact that thermal fatigue causes considerable softening, and that the initial ranking in hardness among the different steels is unaffected by thermal cycling. The cyclic thermal crack growth rate increases roughly with one order of magnitude when increasing the maximum cycle temperature from 700 to 850°C. In addition, an increase in the maximum cycle temperature from 600 to 700°C and from 700 to 850°C reduces the thermal fatigue life with roughly one order of magnitude, respectively.

Three-dimensional thermal crack growth in self-stressed bimaterial joints: Analysis and experiment

A systematic examination of the initiation and growth of thermal cracks in three-dimensional self-stressed bimaterial joints has been performed by using special models consisting of two segments of different materials, for example of glass and aluminum, and by using a well-defined cooling procedure. Besides, the initiation and development of these thermal cracks originating at one corner of such a bimaterial joint have been measured by means of a special image-processing technique. The corresponding mixed boundary value problem has been formulated, and the fracture mechanical assessment of the three-dimensional thermal crack growth has been evaluated by applying the finite element method. Fracture mechanical parameters have been obtained by two different numerical approaches both based on the FE-method. The first approach is based on Irwin's modified crack closure integral by using the so-called 3DMVCCI-technique. As a second method, the well-known J-integral has been implemented in a FE-postprocessor on the basis of the equivalent domain integral (EDI) technique. An appropriate crack growth criterion has been established in accordance with the experimental results obtained.

Thermal cracking of two-phase composite structures under uniform and non-uniform temperature distributions

In this paper curved thermal crack growth in self-stressed brittle solids subjected to well-defined temperature fields has been studied. The resulting boundary-value problems of the stationary plane thermoelasticity are solved by means of the finite element method. Moreover, by applying an appropriate crack growth criterion based on the total energy release rate of a quasistatic mixed-mode crack extension the further development of thermal crack paths starting at the external surfaces of disk-like two-phase compounds with circular cross-sections could be predicted. Several specimen geometries consisting of different material combinations have been investigated by considering uniform temperature changes and by applying the relevant methods of fracture mechanics. Further, the corresponding fracture mechanical data like strain energy release rates and stress intensity factors, respectively, have been determined by additional considerations of the influence of inner stress concentrators onto the paths of quasistatic extending thermal cracks. The comparison of those theoretical investigations with associated cooling experiments shows a satisfying agreement. Finally, the influences of additional local temperature changes onto the prospective thermal crack paths have been studied by means of the fracture criterion mentioned already as well as by using the finite element method. Thereby the numerical results have shown some remarkable effects of interference between the local temperature changes located in the vicinity of thermal crack tips and the further crack paths.

Finite element analysis of thermal crack growth in self-stressed fiber reinforced composites with partially plastified matrices

Finite element analysis of thermal crack growth in self-stressed fiber reinforced composites with partially plastified matrices

Curved thermal crack growth in nonhomogeneous materials with different shaped external boundaries II. Experimental results

The numerical calculations of part I of the paper are compared with experimental investigations concerning the thermal crack growth in different shaped self-stressed two-phase compounds. Thereby fields of experimental principal stress trajectories in stable two-phase solids are obtained by use of the method of photoelasticity. Moreover, the propagation of curved thermal cracks is considered evaluating a series of cooling experiments in two-phase composite structures. The crack paths gained experimentally are compared with theoretical results given in part I of the paper. Finally, fracture mechanical data at the tips of curved thermal cracks are determined by applying the method of caustics. The experimental results show a good agreement with the theoretical calculations presented in part I of the paper.

Curved thermal crack growth in nonhomogeneous materials with different shaped external boundaries I. Theoretical results

Curved thermal cracks are considered running along special principal stress trajectories in self-stressed two-phase solids with different cross sections. The resulting mixed boundary-value problems of the stationary plane thermoelasticity are solved by applying the finite element method. Moreover, using appropriate directional criteria established for crack path prediction, the further extension of thermal cracks starting at the external surfaces of different shaped two-phase solids has been determined. Furthermore, the corresponding fracture mechanical data like crack edge displacements, strain energy release rates and stress intensity factors, respectively, have been calculated. Finally, the theoretical investigations given in part I of the paper are compared with experiments using differing optical methods of the experimental stress analysis. The experimental results reported in part II of the paper and the theoretical calculations show a reasonable agreement.

Quasistatic thermal crack growth in unidirectionally fiber reinforced composite materials

Micromechanical investigations concerning the quasistatic thermal crack propagation in self-stressed unidirectionally reinforced composite structures with a low-fiber volume fraction have been performed. Thus, in order to gain certain microstructural informations about the thermal shock resistance of those reinforced composites different cracked unit cells of several two-phase composites as well as ensembles of such composite microcomponents are considered which are subjected to thermal loading. Therein the principal facets of composite material failure theories, emphazising matrix cracking, fiber breaking and interfacial debonding, respectively, have been studied. The resulting mixed boundary-value problems of the stationary plane thermoelasticity are solved numerically by using standard finite element programs. Further, the influences of the fiber diameters, different shapes of the fiber-matrix interfaces as well as of the external boundaries of the microcomponents on the crack opening displacement u y c and the opening mode stress intensity factor K I , respectively, have been investigated. Numerical results are given for an Al 2O 3 matrix/Molybdenum fiber composite by consideration of different crack configurations.

Curved thermal crack growth in a bounded brittle two-phase solid

Curved thermal crack growth in a bounded brittle two-phase solid

Quasistatic thermal crack growth in the viscoelastic matrix material of a brittle fiber reinforced unit cell

Quasistatic thermal crack growth in the viscoelastic matrix material of a brittle fiber reinforced unit cell