Cyclic Thermal Stress Research Articles

Substantiation of the critical structural and mechanical state of low-alloy heat-resistant steel from steam pipelines of thermal power plant

The paper discusses metallographic studies and the results of mechanical testing of 15Kh1M1F (DIN 15CrMoV5-10) steel in the initial state and after its long-term operation in the steam pipeline of TPP. The revealed adverse impact of shutdowns of TPP units on the structural and mechanical state of steel is associated with the occurrence of cyclic thermal stresses in the pipe walls. Structural changes in metal across the pipe wall are uneven and consistent with regularities of mechanical properties changes. Intergranular fragments detected on the background typical transgranular relief of specimen’s fracture surfaces are considered fractographic signs of steel’s degradation. The part of intergranular fracture in the unit area of the fracture surfaces is proposed as the quantitative indicator of the changes in the structural and mechanical state of 15Kh1M1F steel due to its degradation. The critical state of steel is substantiated based on the regularities of operational changes in its mechanical properties and the revealed fractographic features.

Study on the whole life cycle integrity of cement interface in heavy oil thermal recovery well under circulating high temperature condition

Cement seal failure is common in heavy oil thermal recovery wells, but the effects of steam stimulation on wellbore interface seal performance is unclear. The finite element model of plastic zone formation of cement sheath during high temperature circulating is established. The damage variable of the cement sheath is proposed to define the elastic-plastic transformation process of cementing interface, the interfacial debonding and micro-annulus size caused by thermal stress cycling are quantified, and the effects of key parameters such as steam injection temperature, cycle times, mechanical properties of cement sheath on the change of interface integrity are clarified. The results show that the tensile failure of cement sheath and the micro-annulus always formed on the inner wall of cement sheath, and outer wall remains intact. Excessive steam injection temperature (360 °C–420 °C) will cause an 8–45 μm micro-annual, excessive elastic modulus of cement sheath (>10 GPa) will cause a 20–62 μm micro-annular, the cement sheath with heat shrinkage property will form a 47–54 μm micro-annulus. Based on the sensitivity analysis, the matching relationship between the thermal cycle construction parameters and the performance index of cement sheath is established. The results can provide a reference for the design of cement parameters and engineering parameters under the thermal stress cycles.

High Heat Flux Testing of Graded W-Steel Joining Concepts for the First Wall

The realization of the first wall (FW), which is composed of a protective tungsten (W) armor covering the structural steel material, is a critical challenge in the development of future fusion reactors. Due to the different coefficients of thermal expansion (CTE) of W and steel, the direct joining of them results in cyclic thermal stress at their bonding seam during the operation of the fusion reactor. To address this issue, this study benchmarks two joining concepts. The first concept uses an atmospheric plasma sprayed graded interlayer composed of W/steel composites with a varying content of W and steel to gradually change the CTE. The second concept uses a spark plasma sintered graded interlayer. Furthermore, in order to benchmark these concepts, a directly bonded W-steel reference joint as well as a W-steel joint featuring a vanadium interlayer were also tested. These joints were tested under steady-state high heat flux cyclic loading, starting from a heat flux of 1 MW/m2 up to 4.5 MW/m2, with stepwise increments of 0.5 MW/m2. At each heat flux level, 200 thermal cycles were performed. The joints featuring a sintered graded interlayer survived only until 1.5 MW/m2 of loading, while the joint featuring plasma sprayed graded interlayer and V interlayer survived until 3 MW/m2.

Study on the Solder Joint Reliability of New Diamond Chip Resistors for Power Devices

New diamond chip resistors have been used in high-power devices widely due to excellent heat dissipation and high-frequency performance. However, systematic research about their solder joint reliability is rare. In this paper, a related study was conducted by combining methods between numerical analysis and laboratory reliability tests. In detail, the shape simulation and thermal cycling finite element simulation for solder joints with different volumes were carried out. The optimized solder volume was 0.05 mm3, and the maximum thermal cycling stress under the optimized shape was 38.9 MPa. In addition, the thermal cycling tests with current and high temperature storage tests were carried out for the optimized solder joint, which showed good agreement with the simulation results, clarified the growth and evolution law of intermetallic compound at the interconnection interface, and proved the optimized solder joint had great anti-electromigration, temperature cycling and high temperature storage reliability. In this work, an optimized solder joint structure of a diamond chip resistor with high reliability was finally obtained, as well as providing considerable reliability data for the new type of diamond chip resistors, which would boost the development of power devices.

Control of thermal strain and residual stress in pulsed-wave direct laser deposition

Components manufactured by direct laser deposition (DED) are prone to produce excessive residual stress due to its rapid heating by laser and cooling. Excessive residual tensile stress leads to cracking of deposited sample, even cause failure to serve. Understanding thermodynamic behavior during processing is critical for controlling residual stress. In this study, in-situ transient strain and temperature gradient evolution of each layer on deposited sample 316L stainless steel thin wall during DED using both continuous-wave (CW) and pulsed-wave (PW) laser modes were emerged by digital image correlation (DIC) method and thermal imager. The longitudinal residual stress of deposited sample was evaluated using two laser modes. The results demonstrated that the PW mode creates a smaller temperature gradient and hence a lesser thermal strain than the CW mode. Furthermore, the cyclic thermal stress characteristics of PW mode was observed. All these factors contribute to the reduction of residual stress.

Simulation of Series Resistance Increase through Solder Layer Cracking in Si Solar Cells under Thermal Cycling

In solar cell modules, thermal cycling stresses can cause cracking in the ribbon wire, leading to an increase in series resistance and a drop in the power output of the module. Quantitative analysis was conducted to study the increase in series resistance, considering two cracking models: continuous and random. In the continuous model, it was expected that if all the ribbon wires on the front side of the module cracked, the current would decrease linearly from 0 to 100%, and the series resistance would increase exponentially to infinity. In the random crack model, the current dropped slowly, and the series resistance increased less compared with that in the continuous one. A mathematical model based on the bypass mechanism of the currents was proposed to explain the differences between the two models. The study found that cracking in the solder layer under thermal cycling can be described by a combination of continuous and random models, which can represent the upper and lower levels of the series resistance increase. When the solar cell power dropped to 80%, the increase in series resistance was expected to be in the range of 200 to 250% using the continuous and random models, respectively.

Dissimilar welding of austenitic and ferritic steels using nickel and stainless-steel filler: Associated issues

The microstructure development and mechanical behaviour of dissimilar metal welds between ferritic and austenitic steel, as well as their application in nuclear power plants, are discussed in this review paper. Nuclear reactor components, such as steam generators and pressure vessels, consist primarily of SA508 due to their low cost and high operating temperatures and pressures. The welding of dissimilar metals is crucial due to variations in physical characteristics such as thermal conductivity, thermal expansion coefficient, mechanical properties and chemical compositions. The principal challenges of dissimilar ferritic and austenitic steel welding are the subject of this review work. Weldability issues include a sharp change in mechanical and metallurgical characterization across the fusion line, carbon migration, cyclic thermal stresses and residual stresses, which necessitate a thorough investigation of the welded joint. Generally, austenitic steel and nickel-based fillers are used to join austenitic and ferritic steel materials; however, owing to many weldability concerns, nickel-based consumables are replacing austenitic consumables. Another critical issue in the weld joint is the selection of appropriate welding consumables, and detailed explanations of the benefits of employing a buttering layer on the ferritic side are provided. The effect of heat treatment on the metallurgical and mechanical characteristics of the weld joint, as well as the formation of residual stress, has also been thoroughly explored.

Literature Review on Thermomechanical Modelling and Analysis of Residual Stress Effects in Wire Arc Additive Manufacturing

The wire arc additive manufacturing (WAAM) process is a 3D metal-printing technique that builds components by depositing beads of molten metal wire pool in a layer-by-layer style. Even though manufactured parts commonly suffer from defects, the search to minimize defects in the product is a continuing process, for instance, using modeling techniques. In areas where thermal energy is involved, thermomechanical modeling is one of the methods used to determine the input thermal load and its effect on the products. In the WAAM fabrication process, the thermal load is the most significant cause of residual stress due to the extension and shrinkage of the molten pool. This review article explores the thermomechanical effect and stress existing in WAAM-fabricated parts due to the thermal cycles and other parameters in the process. It focuses on thermomechanical modeling and analysis of residual stress, which has interdependence with the thermal cycle, mechanical response, and residual stress in the process during printing. This review also explores some methods for measuring and minimizing the residual stress during and after the printing process. Residual stress and distortion associated with many input and process parameters that are in complement to thermal cycles in the process are discussed. This review study concludes that the thermal dependency of material characterization and process integration for WAAM to produce structurally sound and defect-free parts remain central issues for future research.

Dislocation structures formation induced by thermal stress in additive manufacturing: Multiscale crystal plasticity modeling of dislocation transport

The motion of dislocations governs the plastic deformation of crystalline materials, which in turn determines the mechanical properties. The complex thermal history, large temperature gradients and high cooling rates during the process of additive manufacturing (AM) can induce high dislocation density and unique dislocation structures in the material. The origin of these dislocation structures and their stability during mechanical loading are debated. A novel temperature dependent continuum dislocation dynamics (CDD) model is developed, in which four state variables are used for each slip system representing the total dislocation density, edge and screw geometrically necessary dislocation densities and dislocation curvature. The CDD model is fully coupled with a crystal plasticity solver, which captures the plastic deformation induced by the dislocation motion. A hybrid continuous and discontinuous Galerkin formulation is developed to accurately reproduce the dynamics of highly discontinuous dislocation density fields that are typical of dislocation structures. A multiscale modeling approach is used, in which the thermally induced deformation in specific grains of a polycrystal is extracted from larger scale crystal plasticity simulations of the laser powder-bed fusion process, and is then used for single crystal scale dislocation dynamics simulations. Simulation results reveal the dynamics of dislocation structure formation in grains at different positions during laser scanning and cooling stages. The effect of the cyclic thermal stress during multi-layer AM fabrication is also investigated. The simulations provide a new perspective on the specific conditions that should be satisfied during AM process for the formation of stable dislocation structures.

Thermal fatigue and cracking behaviors of asphalt mixtures under different temperature variations

Thermal cracking is one of the most annoying distresses in asphalt pavements. The cracking of asphalt pavements caused by extremely low temperature and the damage of thermal fatigue caused by repeated temperature variations are particularly pronounced. The service condition of asphalt pavements has been affected significantly. Laboratory experiments with cyclic loads simulating the actions caused by repeated temperature variations on pavements have been conducted in many previous studies to investigate the thermal fatigue characteristics of asphalt mixtures. In those studies, an equivalent cyclic mechanical stress that can be applied by an actuator was mostly used to replace the cyclic thermal stress induced by a temperature variation. It could simplify the experimental process but could not consider the performances of asphalt mixtures varying as a function of temperature. In the present study, the thermal fatigue properties and cracking behaviors of asphalt mixtures were comprehensively investigated through a modified thermal stress restrained specimen test (TSRST) and the numerical analysis. Various temperature ranges (-20 to −10 °C, −10 to 0 °C), cyclic cooling rates (10 °C/h, 20 °C/h), low-temperature performance cooling rates (10 °C/h, 8 °C/h, 6 °C/h, 4 °C/h, 2 °C/h) and pre-crack dimensions were considered for the study to address the influences of those parameters on the analysis results. Based on the testing and simulation results, it was found that the effects of thermal fatigue on asphalt mixtures under different temperature variations and cooling rates were quantified, and the damage characteristics of the asphalt mixtures were also explored. The results showed that under the low-temperature performance state, the thermal stress of asphalt mixtures increases with a uniform cooling rate and it could be obtained that the faster the cooling rate, the larger the thermal stress generated. In the cyclic thermal stress test, due to the viscoelastic properties of asphalt mixtures, the thermal stress showed significant stress relaxation phenomena under the temperature variations. The magnitude of thermal stress decreased gradually within each cycle. It demonstrates that under the same temperature variation, the thermal stress decreases continuously with the increasing thermal cycles. Through the numerical simulation, it was clear that under different temperature ranges and cooling rates, the magnitude of thermal stress increased with the temperature range decreased, whereas the magnitude of thermal stress increased with an acceleration of the cooling rate. The lower temperature range induced a larger stress intensity factor (KI), which implies a faster cracking evolution. Analyzing the effects of different pre-crack dimensions on the number of temperature cycles, the height of pre-crack showed significant effects on the number of temperature cycles than width.

Design of a Self-Management Solar Pyrolysis Packed-Bed Reactor by Coupling Thermal Energy Storage

A new packed-bed reactor coupled with thermal energy storage (TES) for solar pyrolysis of biomass is developed to overcome the shortcomings of solar energy. The numerical model of a 3.5 kW reactor is formulated by coupling heat and mass transfer balances to chemical kinetics for biomass pyrolysis. It is solved numerically by finite element techniques. The model is applied to analyze the influence of the storage component on the thermal and chemical performance of the pyrolysis process. A new criterion Y defined as the ratio of the char yield and the effective solar power input is proposed to evaluate the effectiveness of solar power input. Under different solar radiation conditions, the coupled TES reduces the solar energy consumption for the char production by over 16%. The storage component can alleviate the overheating and thermal cyclic stresses on the absorption surface. As compared to the non-TES design, the new design can decrease the temperature fluctuation on the absorption surface for over 300 K during solar intermittencies. Moreover, the latent heat in the storage component makes the pyrolysis process stable. Under short-term interruptions, the variation of char yield in the terminal temperature range of 623–673 K is as large as 34.9% in the non-TES design, and it can be decreased to 16.5% after coupling TES. This value can also be decreased from 66.8% to 17.0% under long-term interruptions by coupling the storage.

Novel form-stable phase change materials with enhancing crystallization rate for thermal energy storage

Enhanced thermal conductivity form-stable phase change materials (PCMs) have attracted much attention since their stable shape and improved thermal storage efficiency, but how to balance the relationship between enthalpy and function is still a formidable challenge. In this work, the semi-interpenetrating polymer network (semi-IPN) structural sodium polyacrylate (PAAS)/N,N′-Methylenebisacrylamide (MBA)/polyethylene glycol (PEG) was combined with the high compatible polyvinylpyrrolidone (PVP)/PEG/Cu nanoparticle (CuNP) by in-situ doping and radical polymerization to construct an enhanced thermal conductivity and fast crystallization system with strong form stability. The phase change enthalpy of the material was unaffected by the CuNP (112.9 J/g), on the contrary, the heating and cooling rates were enhanced by 30.36 % and 27.97 %. Moreover, the CuNP also acted as crystal nucleus to improve the crystallization rate (55.00 %). The constructed structure exhibited high resistance to cyclic thermal stress and reached the enhancement of the thermal conductivity and the form stability simultaneously.

Stability assessment of Polatuzumab vedotin and Brentuximab vedotin using different analytical techniques

Antibody-drug conjugates (ADC) are considered to be fast-growing innovative biopharmaceuticals. The science used for conjugating potent cytotoxic payload to the targeted monoclonal antibody through a chemical linker has played a great value in the area of oncology treatment. In this study; Polatuzumab vedotin (POLA) and Brentuximab vedotin (SGN-35) were subjected to various stress conditions enclosing different pH, thermal stress, agitation, and successive cycles of freeze and thaw in order to produce potential degradation by-products and guarantee the appropriateness of the applied testing protocol. Different analytical techniques were established and validated to be used in the quantitation of the degraded products from different perspectives. The formation of ADC aggregates and fragments was monitored using SE-HPLC as well as dynamic light scattering (DLS). The drug antibody ratio (DAR) and ADC conjugation profile were determined using hydrophobic interaction chromatography (HIC-HPLC). In addition to performing a statistical interpretation of HIC-HPLC results by principal component analysis (PCA) to explicate the obtained data. Also, the quantity of the unconjugated toxic drug was quantified using RP-HPLC. Testing the binding activity of ADC to their target receptor ADC was conducted using ELISA. Results presented that used assay protocol had worked as a complementary design for characterization and stability assessment of the used ADC. Variances in the stability profile of both products were observed which could be attributed to the usage of different formulation buffers. This highlighted the importance of using multiple techniques for the assessment of the quality attributes of such sophisticated products. The analytical assay protocol should be used for the evaluation of the quality and stability of several ADC.

Thermal-cycling stress studies to support transport and distribution of liquid dosage forms

Thermal-cycling stress studies to support transport and distribution of liquid dosage forms

Influence of R-Ratio on Fatigue of Aluminum Bonding Wires

Bonding wires made of aluminum are the most used materials for the transmission of electrical signals in power electronic devices. During operation, different cyclic mechanical and thermal stresses can lead to fatigue loads and a failure of the bonding wires. A prediction or prevention of the wire failure is not yet possible by design for all cases. The following work presents meaningful fatigue tests in small wire dimensions and investigates the influence of the R-ratio on the lifetime of two different aluminum wires with a diameter of 300 µm each. The experiments show very reproducible fatigue results with ductile failure behavior. The endurable stress amplitude decreases linearly with an increasing stress ratio, which can be displayed by a Smith diagram, even though the applied maximum stresses exceed the initial yield stresses determined by tensile tests. A scaling of the fatigue results by the tensile strength indicates that the fatigue level is significantly influenced by the strength of the material. Due to the very consistent findings, the development of a generalized fatigue model for predicting the lifetime of bonding wires with an arbitrary loading situation seems to be possible and will be further investigated.

Fast Quasi-Static Time-Series Simulation for Accurate PV Inverter Semiconductor Fatigue Analysis with a Long-Term Solar Profile

Power system simulations with long-term data typically have large time steps, varying from one second to a few minutes. However, for PV inverter semiconductors in grid-connected applications, the minimum thermal stress cycle occurs over the fundamental grid frequency (50 or 60 Hz). This requires the time step of the fatigue simulation to be approximately 100 μs. This small time step requires long computation times to process yearly power production profiles. In this paper, we propose a fast fatigue simulation for inverter semiconductors using the quasi-static time-series simulation concept. The proposed simulation calculates the steady state of the semiconductor junction temperature using a fast Fourier transform. The small thermal cycling during a switching period and even over the fundamental waveform is disregarded to further accelerate the simulation speed. The resulting time step of the fatigue simulation is 15 min, which is consistent with the solar dataset. The error of the proposed simulation is 0.16% compared to the fatigue simulation results using the complete thermal stress profile. The error of the proposed method is significantly less than the conventional averaged thermal profile. A PV inverter that responds to a transactive energy system is simulated to demonstrate the use of the proposed fatigue simulation. The proposed simulation has the potential to cosimulate with system-level simulation tools that also adopt the quasi-static time-series concept.

Coarsening of metal/ceramics bicontinuous structures enhanced by stress-induced instability under cyclic thermal stress

When a two-phase material has a bicontinuous and interpenetrating structure, the coarsening process during thermal annealing involves complex changes in morphology. Such a bicontinuous two-phase (solid/solid) structure is formed by sintering mixed metal and ceramic powders. This structure is used for electrodes in electronic devices. Here we demonstrate clearly that the coarsening of bicontinuous solid/solid two-phase material is accelerated by stress-induced instability similar to the ATG instability occurring in thin films. We used a metallic heating element embedded in a ceramic substrate as a model. The coarsening of Pt/alumina bicontinuous structure was enhanced by thermal stress during heating and cooling cycles. The coarsening was not appreciably affected by the electric current in Joule heating. The coarsening of the bicontinuous structure leads to the electrical breakdown of the electrodes. The analysis of stress-induced instability provides methods for improving the lifetime and reliability of electronic devices under thermal cycling.

Zebrafish parental progeny investment in response to cycling thermal stress and hypoxia: deposition of heat shock proteins but not cortisol.

The maternal match hypothesis predicts that maternal exposure to a stressor may help prepare offspring to cope with the same disturbance in later life. Although there is support for this hypothesis, the signals involved in non-genetic inheritance are unclear. In this study, we tested how adult zebrafish exposure to diel cycles of thermal stress (27-36°C), hypoxia (20-85% dissolved oxygen) or the combined treatment affects maternal and embryonic levels of cortisol and heat shock proteins (HSPs). While parental exposure to the thermal, hypoxic or combined treatment for 2 weeks did not affect whole-body cortisol levels, the combined exposure increased ovarian cortisol levels by 4-fold and reduced embryonic cortisol content by 60%. The combined treatment also elicited 3- and 19-fold increases in embryo transcripts involved in cortisol breakdown (11bhsd2) and export (abcb4), respectively. The thermal stress and combined exposure also elicited marked increases in ovary and embryo hsp70a (20- to 45-fold) and HSP70 (3- to 7-fold), and smaller increases in ovary and embryo hsp90aa and hsp47 (2- to 4-fold) and in embryo HSP90 and HSP47 (2- to 6-fold). In contrast, except for increases in ovary hsp90aa (2-fold) and embryo HSP90 (3-fold), the hypoxia treatment had little effect on HSP expression and transfer. Overall, while the embryonic deposition of HSPs largely paralleled the ovarian cellular stress response, the inverse relationship between ovary and embryo cortisol levels suggests the existence of barriers against cortisol deposition in response to environmental stressors. We conclude that the endocrine and cellular stress responses make stressor-specific and distinct contributions to non-genetic inheritance.

High temperature oxidation of SiC-coated Fe-Cr-Al-Mo alloys in muffle and concentrated solar furnaces

The maximal temperature of a solar receiver is limited by its resistance to oxidation, thermal cycling and mechanical stresses as it is a key component of solar power plant with a central tower. Currently used Ni-based alloys cannot heat the air coolant at temperatures beyond 1000 K due to the severe oxidation that may affect the surfaces exposed to air at high temperatures, affecting the solar absorptivity of the receiver. A SiC coating should protect a high temperature metallic alloy from oxidation and improve its solar absorptivity, only if the accommodation between the metallic substrate and the ceramic coating is optimized to prevent the coating from cracking and peeling due to the thermal expansion of the assemblage. To reduce the interfacial stresses, SiC was deposited using High Temperature Chemical Vapor Deposition on a pre-oxidized Fe-Cr-Al-Mo alloy, so that a 2µm-thick alumina layer could work as an accommodation layer. The oxidations performed in muffle and solar furnaces (associated to ex situ characterizations using scanning electron microscopy and energy-dispersive X-ray spectroscopy mapping, X-ray diffraction, and room-temperature normal spectral emissivity measurements) have demonstrated that this multilayer structure could support long-term oxidation and thermal stresses up to1400 K without significant changes regarding the spectral emissivity, but the coating peels if the sample is treated at 1600 K. The multilayer structure can therefore work beyond the current working point of solar receivers, nevertheless the accommodation still has to be improved in case of accidental exposures to higher solar fluxes.

Experimental study on the evolution of mechanical properties of hot dry rocks under alternating temperature loads

Inspired by the physical process of thermal expansion and cold shrinkage, this study proposes a new idea to improve the capacity to form complex fractures (i.e., fracability) in hot dry rock (HDR) under alternating temperature loads. However, the evolution of the HDR mechanical properties under alternating temperature loads is rarely reported. This study analyzed the evolution mechanism of the HDR rock mechanics properties under alternating temperature loads by using the high-temperature high-pressure rock mechanics triaxial test system. The results show that mechanical parameters such as compressive strength, dilatancy stress, and elastic modulus are significantly reduced after alternating temperature loading, compared with those after simple heat treatment. After alternating temperature loading, compared with the case of simple heat treatment, the HDR rock samples reach the dilatancy stress earlier; its stress-strain curve features a visible concave arc at the micro-fracture closure segment; the axial loading ends up with the shear failure and enhanced complexity. The microstructural analysis shows that cyclic thermal stress occurs inside the HDR as the temperature increases and extensive mineral metasomatism is triggered, which is dominated by quartz penetrating plagioclase via metasomatism. Therefore, the decrease of quartz content and the HDR mineral metasomatism under alternating temperature loads are the fundamental causes for the great changes in the HDR mechanical properties.