Number Of Thermal Shock Cycles Research Articles

Evolution mechanism of permeability of hot dry rock under coupled effect of thermal fatigue and seawater interaction during coastal geothermal development

Using seawater as a heat transfer fluid for developing hot dry rock (HDR) geothermal energy in coastal areas is a frontier of engineering worth exploring; however, only a few studies have considered this research topic. During the development of HDR based on enhanced geothermal system (EGS) technology, the thermal shock fatigue effect of low-temperature seawater on high-temperature reservoirs leads to changes in the permeability of the HDR, notably impacting the reservoir reconstruction design and heat transfer efficiency. Accordingly, the changes in pore structure, pore distribution, porosity, and permeability of HDR in the Guangdong-Hong Kong-Macao Greater Bay Area were investigated based on nuclear magnetic resonance (NMR) techniques and fractal theory after treatment to different temperatures and numbers of thermal shocks due to seawater interaction. The experimental results showed that with an increase in temperature and the number of seawater interactions, the pore structure distribution of the HDR underwent significant changes, with the proportion of mesopores and macropores increasing by 24.29 % and 10.52 %, respectively. Moreover, the porosity and permeability increased with increasing temperature and number of thermal shock cycles, especially above 300 °C. When the temperature increased from 100 °C to 500 °C, the total porosity increased from 0.98 % to 3.85 %, an increase of 292.9 %, while the permeability increased from 10−4 mD to 0.1 mD, an increase of nearly 1000 times. Changes in the pore structure, pore distribution, porosity, and permeability of HDR are caused by multiple damage mechanisms related to high-temperature nonlinear expansion, thermal shock effects, chemical erosion, and fatigue. Additionally, the permeability of the HDR after seawater treatment at the same heat treatment temperature and number of thermal shocks was higher than that after freshwater treatment. At a temperature of approximately 500 °C and 20 thermal shocks, the permeability of HDR under the action of seawater was approximately seven times that of fresh water. Therefore, these results suggest that using seawater as a heat transfer fluid has more advantages in enhancing the permeability of reservoirs.

Hydrothermal synthesis of HfC whiskers and its toughening effect on ZrB2-HfO2 coatings

Hafnium carbide (HfC) whiskers were successfully synthesized by combining hydrothermal and carbothermal reduction. The precursor of HfC whiskers was prepared by the hydrothermal method, subsequently pyrolyzed, and reduced to HfC whiskers at 1500–1700 °C. The synthesis parameters of HfC whiskers at various temperatures, C/Hf molar ratios, and NaF concentrations were investigated in detail. The whiskers with diameters of 1–3 μm and lengths of 50–90 μm were prepared by pyrolyzing the precursors with a C/Hf molar ratio of 6 at 1700 °C. The experimental results and thermodynamic analysis demonstrated that the growth of HfC whiskers was governed by the vapor-liquid-solid (VLS) mechanism. Furthermore, the prepared HfC whiskers were added to the ZrB2-HfO2 coatings on the surface of tungsten-rhenium substrates in different ratios to toughen the coatings. The thermal shock test results indicated that the coatings toughened with HfC whiskers had better thermal shock resistance. In particular, the maximum number of thermal shock cycles that 6%HfCW-ZH could withstand was five times higher than that of W–Re alloy and about one time higher than that of ZH coatings without HfC whiskers. The thermal shock resistance of the ZrB2-HfO2 coatings was significantly improved by adding HfC whiskers.

Interface stress calculation and failure behavior of TBCs on the surface of aluminum alloy with anodic oxidation

Aluminum protective coatings have poor performance due to the significant difference in coefficient of thermal expansion (CTE) between the substrate and the coating. In this study, porous anodic aluminum layer, which have high bonding, well matching and grew in situ on the substrate of aluminum alloy (4032) using anodic oxidation, and then thermal barrier coatings were produced on the surface by laser surface modification and atmospheric plasma spraying (APS). The aim of this way is to improve the interface thermal shock resistance (TSR) of the coatings. The results showed that the coatings with anodic aluminum layer (highest group average of 444 cycles) have a much higher number of thermal shock cycles than metallic bond coatings. Furthermore, the failure analysis suggested that the bonding stability of the coatings is influenced by the surface state, surface mosaic structure, as well as such as CTE and surface roughness. Eventually, a double-layer mismatch stress model was developed to characterize the residual stresses caused by deformation mismatch in the coatings. After performing calculations，from a force perspective τa≈10τb, and from a work perspective Wfa≈3.34Wfb.

Thermal fatigue characteristics of 8Y2O3-ZrO2, La2Zr2O7, La2(Zr0.7Ce0.3)2O7 and La2Ce2O7 thermal barrier coatings in duplex, multilayer functionally graded and multilayer configurations

La2Zr2O7, La2(Zr0.7Ce0.3)2O7 and La2Ce2O7 pyrochlore plasma sprayable powders were synthesized and plasma spray coated on steel plates with NiCrAlY bond coat. Three different configurations were used: duplex, multilayer functionally graded and multilayer, with different combinations of commercial 8% yttria stabilized zirconia (8YSZ) and NiCrAlY (bond coat) layers. The prepared coatings were compared with the standard duplex 8YSZ thermal barrier coatings (TBCs) with a goal to study their suitability to serve as TBCs. TBCs? layer thicknesses and interfaces were studied via SEM on polished cross section metallographic samples removed from the spray coated TBCs. Thermal fatigue resistance was evaluated by directing a gas flame on the ceramic surface at 1200 and 1400 ?C, followed by its rapid withdrawal and forced cooling by pedestal fan. The maximum number of thermal shock cycles the coatings could withstand before failure was determined. The multilayered TBCs with lanthanum cerate composition stacked with 8YSZ exhibited the superior thermal fatigue resistance characteristics compared to all other studied TBCs. The findings were correlated with the crystalline phases of the ceramic coatings, obtained via XRD, and discussed in the light of existing literature.

Coatings toughened with nano-HfO2 fibers to improve the thermal shock resistance of W-26Re alloys

W–Re alloys find wide application in high-temperature measurements and as components of engines and aircraft. However, their low oxidation and thermal shock resistances have limited their application at high temperatures in oxidized atmospheres. In this work, an inner WSi2 coating was first prepared on the surface of the W-26Re alloy by pack cementation. Subsequently, an outer ZrB2-HfO2-SiC (ZHS) coating was prepared by the sol-gel method and blade coating, using self-prepared nano-HfO2 fibers introduced in different ratios (0%, 3%, 6%, and 9%). Following thermal shock tests at 1073–1773 K, the coatings toughened by nano-HfO2 fibers with high melting point (above 3000 K) showed better thermal shock resistance, especially the 6% HfO2-doped coatings. The 6%Hf-ZHS coating underwent the highest number of thermal shock cycles (369), 385.5% and 210.1% higher than those experienced by W-26Re and ZHS. In addition, the thermal shock resistance of ZHS was 56.6% better than of the bare W-26Re alloy. Finally, the protection mechanism of the above coatings was explained by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses.

Principal component analysis of morphological descriptors for monitoring surface defects induced by thermal shock

Pattern recognition techniques are applied to various morphological descriptors to monitor the formation and propagation of surface defects of materials subjected to thermal shock. A low-cement high-alumina castable was synthesized, cured, sintered, and exposed to thermal stability testing using the water quench test. After a certain number of thermal shock cycles, photographs of the samples’ surfaces were taken and subjected to image analysis. The influence of the sintering temperature on the morphology of the detected defects was studied using principal component analysis (PCA) as a pattern recognition technique that is the most informative for extracting possible differences. The morphological descriptors of the defects correspond to the previous results regarding the influence of sintering temperature on the structure of a castable during thermal shocks.

Experimental study on the evolution of pore-fracture structures and mechanism of permeability enhancement in coal under cyclic thermal shock

Heat injection is a new method of recovering enhanced coalbed methane (ECBM). In this study, the impact of a sudden increase in ambient temperature on the permeability of coal was studied, and the application prospects of multiple thermal effects in coal fracturing and permeability enhancement were explored. The permeability and development of pore-fracture structures in coal were tested before and after cyclic thermal shock. The evolution characteristics of the pore distribution were evaluated, and an empirical formula for estimating the permeability growth of coal was established. Digital image processing technology and fractal theory were used to analyse changes in macroscopic fractures. The results indicates that cyclic thermal shock could effectively promote the generation and expansion of permeability pores, effectively connect the relatively independent fracture structures, and break and expand the microfractures and pore groups to form an interwoven fracture network. The increase in cyclic thermal shock resulted in an increase of 0.92%, 1.13%, and 16.15% in total porosity increment, the porosity increment of seepage pores and the proportion increment of seepage pores, respectively, after seven thermal shocks. The permeability of coal exhibited a logarithmic growth pattern with an increase in the number of thermal shock cycles; the average permeability increased by 100.02% after seven cycles. Based on the theory of thermodynamics, the influencing mechanism of cyclic thermal shock on the evolution of pore-fracture structures was explored. Differences were observed in the thermal expansion coefficients of minerals in coal, and thermal stress was generated under cyclic thermal shock, which may lead to damage, promoting fracture formation and increasing permeability. With an increase in the number of thermal shock cycles, the efficiency of permeability enhancement gradually decreased, which suggests that the reservoir conditions should be combined and mining plan should be reasonably set in ECBM extraction using multiple thermal injection techniques.

Failure Analysis of Aluminum Wire Bonds in Automotive Pressure Sensors in Thermal Shock Environments

Wire bonding remains one of the most widely adopted interconnection techniques in the field of electronic packaging. At present, the most effective way to ensure a long life and high reliability of wire bonds is to improve the bonding quality. In this study, both experiments and finite element analysis (FEA) were employed to develop a fundamental understanding of wire bond degradation. Sensors with two protective silicone gels were loaded with the same thermal shock at a temperature ranging from $- 40^{\circ }\text{C}$ to 125°C, and the switching time was shorter than 10 s. The number of thermal shock cycles for the aluminum wire covered with transparent silicone reached 1200, but the maximum number of cycles for the other wire only reached 454. The experimental results indicated that the chosen transparent silicone performed better than did the black silicone originally selected, which was also verified by the simulation results. In addition, bond pull and shear tests were performed. The results revealed no degradation of either the Ag-Al or Ni-Al bonding joints under thermal loading. In summary, the root cause of failure was found to be improper protection silicone application, which, as often ignored in analysis, accelerated thermal fatigue of the aluminum wires. An explanation of the observed trend and a recommended aluminum wire bonding method were also provided.

Mechanical reliability of Cu cored solder ball in flip chip package under thermal shock test

A Cu-cored solder ball (CCSB) is often used as the interconnection material for 3D package. The CCSB has a Cu core surrounded by Sn-Ag-Cu alloy. The effect of the Cu core on mechanical reliability of the CCSB was investigated using thermal shock test. Microstructure and thermal shock reliability of the CCSB with organic solderability preservative (OSP) surface finish was compared with that of Sn-3.0wt.%Ag-0.5wt.%Cu (SAC) solder. The thermal shock test was performed in the temperature range of −40 °C to 125 °C in compliance with JESD22-A104. Failure mechanism was analyzed by finite element method analysis. Average number of thermal shock cycles for the CCSB/OSP joints was 1.15 times higher than that for SAC/OSP joints. Maximum value of simulated plastic strain for the SAC/OSP joints was 1.25 times higher than that for the CCSB/OSP joints because the stand-off height of the CCSB/OSP joints could be maintained by the Cu core.

Research on thermal shock resistance of porous refractory material by strain-life fatigue approach

The study aims to investigate the effects of pore structure on the thermal shock resistance of porous refractory materials. Porous material is constituted by a solid frame and the pores filling with air. A direct thermo-mechanical coupling simulation and strain-life approach were employed to predict the number of thermal shock cycles of the materials; thus, influences of the porosity and distribution of pores on the thermal shock resistance were studied. The specimen was subjected to a mechanism of thermal shock damage in which alternating thermal stress under cyclic ‘hot’ and ‘cold’ shock. The simulation results show that the magnitude of thermal stress is large during the thermal shock process. And the residual thermal stresses generate at the solid/air interface since stress gradients occur inside the bulk. Furthermore, higher or lower porosity had no positive effect on the thermal shock resistance of the porous material; the highest thermal shock resistance was attained at a porosity of 20%. The uniform distribution of pores is favorable to improve the thermal shock resistance of materials of high porosity. The validation test results show that the number of thermal shock cycles of the two samples in the experiments were closer to the situations of chaotic pore distributions in the simulations.

Effect of thermal shock cycling on storage stability and quality of fresh-cut potato

To enhance the storage stability and quality of fresh-cut potato, potato cubes with dimensions of 1 × 1 × 1 cm3, 2 × 2 × 2 cm3, and 3 × 3 × 3 cm3 were blanched at 90 °C for 15, 30, or 45 s, followed by soaking in ice-water for 1 min; the treatment was repeated for up to six cycles. The 2 × 2 × 2 cm3 and 3 × 3 × 3 cm3 potato cubes subjected to six thermal shock cycles for cycling times of 30 s and 45 s showed significant lowering of the browning index during storage at ambient temperature. The 1 × 1 × 1 cm3 potato cube was most highly susceptible to browning, although repeated thermal shock cycling reduced the development of browning. A higher number of thermal shock cycles effectively decreased the polyphenol oxidase (PPO) activity of the potato cubes. The reduction of the PPO activity was more pronounced as the sample size decreased. The hardness of the raw and fried samples decreased, along with reduction of the melting enthalpy, as the treatment time and number of cycles increased. The browning index of the fried potato declined as the number of cycles increased.

Effect of thermal shock cycling on the quasi‐static and dynamic flexural properties of flax fabric‐epoxy matrix laminates

ABSTRACTThe aim of the present work is to investigate the influence of thermal shock cycling on the quasi‐static and dynamic flexural properties of epoxy matrix composites reinforced with natural flax fibers fabric. Polymer composite laminates reinforced with four plies of natural flax fiber fabric have been manufactured. The samples have been exposed to different number of thermal shock cycles (0, 50, 100, 200, 300, 400), at a temperature range from −40 °C to +28 °C. Dynamic mechanical analysis (DMA) tests were performed on both pristine and thermally shocked specimens in order to determine their viscoelastic response. Due to the thermal shock cycling and after 100 thermal shock cycles, a maximum decrease in storage and loss modulus on the order of 50% was observed. After 100 thermal shock cycles, no further degradation of dynamic properties was observed. On the contrary, damping factor and glass transition temperature values showed a minor variation as number of thermal shock cycles increased. In addition, the time–temperature superposition principle (TTSP) was successfully applied, confirming the fact that the flax fiber fabric‐epoxy laminate is a thermo‐rheologically simple material. Likewise, quasi‐static three‐point bending tests were executed and a maximum decrease of 20% in flexural strength was observed after 400 thermal shock cycles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48529.

Crack Healing in Mullite-Based EBC during Thermal Shock Cycle

Crack healing phenomena were observed in mullite and mullite + Yb2SiO5 environmental barrier coating (EBC) materials during thermal shock cycles. Air plasma spray coating was used to deposit the EBC materials onto a Si bondcoat on a SiCf/SiC composite substrate. This study reveals that unidirectional vertical cracks (mud cracks) formed after several thermal shock cycles; however, the cracks were stable for 5000 thermal shock cycles at a maximum temperature of 1350 °C. Moreover, the crack densities decreased with an increasing number of thermal shock cycles. After 3000 thermal shock cycles, cracks were healed via melting of a phase containing SiO2 phase, which partially filled the gaps of the cracks and resulted in the precipitation of crystalline Al2O3 in the mullite. Post-indentation tests after thermal shock cycling indicated that the mullite-based EBC maintained its initial mechanical behavior compared to Y2SiO5. The indentation load–displacement tests revealed that, among the materials investigated in the present study, the mullite + Yb2SiO5 EBC demonstrated the best durability during repetitive thermal shocks.

Void fraction of a Sn–Ag–Cu solder joint underneath a chip resistor and its effect on joint strength and thermomechanical reliability

The void fraction in the solder joint of a chip resistor and its effect on the solder joint strength and reliability were investigated. The solder joint of a chip resistor has two regions: solder beneath the component and solder fillet. Although the total void fraction was similar irrespective of the component size, the void fraction of solder beneath the component increased and that of solder fillet decreased as the component size increased. The void fraction decreased considerably under vacuum reflow compared with that under air reflow. Furthermore, the vacuum reflowed samples showed similar void fraction characteristics as the air reflowed samples: the void fraction in the solder beneath the chip resistor increased and that in the solder fillet decreased as the chip resistor size increased. For both air and vacuum reflow, the shear strength of the chip resistor solder joint decreased as the chip size increased. The reliability of the chip resistor joint was evaluated using a thermal shock test. As the number of thermal shock cycles increased, the shear strength of the chip resistor solder joint decreased. Up to 2000 cycles, the shear strength reduction rates were similar irrespective of the component size. However, after 3000 cycles, the shear strength reduction rate of the large components (0805, 1210) was to about 50%, which was twice that of the small components (0402, 0603). Cross-sectional SEM after the thermal shock test revealed that a generated crack merged with a void, forming a long crack and lowering the joint reliability.

The influence of temperature gradient thermal shock cycles on the interlaminar shear strength of fibre metal laminate composite determined by the short beam test

The paper presents research on the interlayer adhesion of fibre metal laminate composites in a 3/2 configuration made of 0.4 mm thick 2024-T3 ALCLAD aluminium sheets. A polymer-fibrous layer is used to make a prepreg based on glass fibres with a thermosetting epoxy matrix. Experimental research presented in this paper was aimed at determining the impact of thermal shocks on the mechanism of composite destruction in the three-point-bending test. The samples were subjected to 100 °C temperature gradient thermal shocks in the form of cyclic temperature changes in the range of −40 °C and +60 °C. The number of cycles was 500 and 1000, according to the specific variant. The damage characteristics were observed by Scanning Electron Microscopy to assess failure modes. Samples subjected to thermal shocks are characterised by lower stiffness in relation to samples not exposed to repeated thermal shocks. It was found that both the failure mode and interlaminar shear strength depend on the number of thermal shock cycles. Under the influence of cyclic temperature changes in the test samples, metallic layers undergo cyclic expansion and shrinkage while the layer of fibre-reinforced composite with relatively low thermal expansion does not undergo large deformations.

Influences of gap size and cyclic-thermal-shock treatment on mechanical properties of TLP bonded IN-738LC superalloy

Abstract Influences of gap size and cyclic-thermal-shock treatment on the mechanical properties of transient liquid phase (TLP) bonded IN-738LC superalloy were investigated. For this purpose, TLP bonding of IN-738LC superalloy was carried out in a vacuum furnace using powdered AMS 4777 as the filler metal. The results showed that isothermal solidified zone (ISZ) consisted of Ni solid-solution and the distribution of alloying elements was homogeneous. High hardness of HV 409 and high shear strength of 506 MPa were observed in 40 μm gap sample. Alloying elements formed γ′ precipitates and the solid-solution in the ISZ. Hardness and shear strength of bonds were reduced with increasing the gap size (in range of 40–120 μm). The fractured surfaces of complete isothermal solidified bonds showed dimpled rupture, but athermal solidified bonds showed cleavage fracture surface. 10, 20, 30 and 40 thermal-shock cycles were applied to 80 μm gap samples, respectively. The shear strength of the bond was measured to be 268 MPa after the 40th thermal-shock cycle. The sample with gap size of 80 μm was failed due to crack nucleation on faying surface at 45th thermal-shock cycle. The amount of the produced brittleness due to quenching the samples in water bath was attributed to the number of thermal-shock cycles.

Mechanical Properties and Thermal Shock Resistance of Rhenium Coating in Iridium/Rhenium/Carbon-carbon Composites

Rhenium is a promising coating material for liquid rocket nozzles because of its extremely superior performance, such as high melting point, high temperature strength and excellent fatigue properties. In this work, Re coating was prepared on fabric-based pierced Carbon/Carbon composite substrate using chemical vapor deposition. Bonding strength, micro hardness and thermal shock resistance of rhenium coating on Carbon/Carbon substrate were investigated respectively. The bonding strength between the coating and the substrate was tested using different methods including tensile tests, shearing tests and micro scratch tests. Thermal shock resistance was investigated by an induction furnace from 2000oC to the room temperature. The morphologies and characteristics of the coatings were studied by scanning electron microscopy. The results indicated that the highest average value of tensile fracture strength is 20.4MPa and shearing fracture strength is 21MPa on Carbon/Carbon composite substrate. The rhenium coating broke up and flaked off near a crack in the scratch test. Micro hardness test suggested that C atoms diffused quickly into the rhenium coating within an hour. The thermal shock lives depended on the number of thermal shock cycles. It is also concluded that rhenium coating had good thermal shock resistant with Carbon/Carbon Composite substrate.

Thermal Shock Properties of a 2D-C/SiC Composite Prepared by Chemical Vapor Infiltration

The thermal shock properties of a two-dimensional carbon fiber-reinforced silicon carbide composite with a multilayered self-healing coating (2D-C/SiC) were investigated in air. The composite was prepared by low-pressure chemical vapor infiltration. 2D-C/SiC specimens were thermally shocked for different cycles between 900 and 300 °C. The thermal shock resistance was characterized by residual tensile properties and mass variation. The change of the surface morphology and microstructural evolution of the composite were examined by a scanning electron microscope. In addition, the phase evolution on the surfaces was identified using an X-ray diffractometer. It is found that the composite retains its tensile strength within 20 thermal shock cycles. However, the modulus of 2D-C/SiC decreases gradually with increasing thermal shock cycles. Extensive pullout of fibers on the fractured surface and peeling off of the coating suggest that the damage caused by the thermal shock involves weakening of the bonding strength of coating/composite and fiber/matrix. In addition, the carbon fibers in the near-surface zone were oxidized through the matrix cracks, and the fiber/matrix interfaces delaminated when the composite was subjected to a larger number of thermal shock cycles.

Effect of thermal fatigue on the mechanical properties of epoxy matrix composites reinforced with olive pits powder

AbstractThis study is focused on the investigation of the effect of thermal shock cycling on the mechanical properties of cellulose based reinforced polymer composites. Polymer composites reinforced with olive pits powder at different filler‐volume fractions were manufactured. An increase in the bending modulus on the order of 48% was achieved. On the other hand, results showed that the bending strength remained almost unaffected from the amount of filler introduced. Next, the effect of thermal shock cycling on the mechanical behaviour of the thus manufactured composites was investigated. Theoretical predictions for both the properties variation with number of thermal shock cycles applied as well as with filler‐volume fraction were derived using the residual properties model (RPM) and the modulus predictive model (MPM), respectively. Predicted values were compared with respective experimental results. In all cases, a fair agreement between experimental findings and theoretical predictions was found. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Deformation analysis for thermal shock using optical sensors and constitutive modelling

Thermal shock is an extreme form of thermo-mechanical loading with high spatial and time-dependent gradients and affects life expectancy of high quality and safety relevant machine components. This paper concentrates on experimental and numerical investigations of cyclic deformations under thermal shock loading. For this purpose two different specimens, a cylinder and a hybrid-forming tool, of hot-working steel (X37CrMoV5-1) are heated up by induction heating and shocked down by sprayed water in a cyclic manner. After a certain number of thermal shock cycles the specimens are analysed with optical measuring equipment to investigate deformations and form changes. The progression of deformation development is observed with respect to the number of thermal shock cycles and the results of the deformation analysis are used for validation of a finite element simulation with a constitutive material model.