Cyclic Thermal Stress Research Articles

A Method for Run-Time Prediction of On-Chip Thermal Conditions in Dynamically Reconfigurable SOPCs

Autonomous mobile systems nowadays deploy FPGA-based System on Programmable Chips (SoPCs) for supporting their dynamic multitask multimodal workloads. For such field-deployed systems, activation times, execution periods of tasks, and variations in environmental conditions are usually difficult to predict. These dynamic variations result in a new challenge of dynamic thermal cycling stress on the SoPC die, which can result in transient and even permanent hardware faults in the computing system. This paper proposes the approach of run-time structural adaptation (RTSA) to mitigate dynamic thermal cycling stress on the SoPC dies. RTSA assumes the tasks to have multiple implementation variants, called Application Specific Processing (ASP) circuit variants, which vary in hardware resources, operating frequency, and power consumption. Dynamically reconfiguring appropriate ASP circuit variants of tasks allow systems to maintain their die temperature in the desired range while taking into account variations in power budget and modes of operation. This means the essence of RTSA is a decision-making mechanism which can select at run-time, a suitable system configuration (set of ASP circuit variants of active tasks), whenever needed, to meet the die temperature constraints. To do so, run-time die temperature prediction for potential system configurations using an estimation model is required. This paper presents a generic method to derive an analytical model for any SoPC that can estimate the die temperature in real time and thus support the decision-making mechanism. To develop this method, the thermal behavior of SoPC die under different task scenarios is studied and relation of die temperature to frequency, resource utilization, and power consumption is analyzed. An RTSA-enabled experimental platform is set up on Xilinx Zynq XC7Z020 SoPC for this purpose. Experimental results also demonstrate that the proposed method can be used to derive a model in run-time, thus enabling systems to self-derive and dynamically update the model in run-time.

Thermal cycling test of solid particles to be used in concentrating solar power plants

Durability and reliability of solid particles to be used in concentrating solar power tower plants is crucial for the project viability. Solid particles materials to be implemented in concentrating solar power plants are thermal aged and thermal cycled in this study to evaluation of solid particles at high temperatures. A homemade device has been developed to perform accelerated-durability tests, that allows emulation of thermal cycling stress from days to years, and even evaluate the 11,000 cycles expected to be reached during 20 years' plant's lifetime in less than four months. A detailed description of the operation of this device is included in this paper. In addition, current solar absorptance, chemical composition, physical properties, thermal characteristics, and morphologic analysis of the samples before and after thermal treatments have been performed. The materials under the study are the most reliable solid particles reported in CSP field: silicon carbide (SiC) and CarboHSP® 30/60. Characterization results show that SiC is more affected on its durability by thermal cycling than by constant temperature aging treatment while CarboHSP® is affected by temperature aging rather than thermal cycling. SiC reacts with oxygen to form SiO2 on the surface, with a positive effect in its solar absorptance. Nevertheless, with thermal cycles, SiC particle surface becomes damaged and the reaction continues with more new exposed surface. Meanwhile, CarboHSP® reduces its solar absorptance with high temperature only due to changes in its surface chemical composition. However, thermal cycling shows no negative effect in CarboHSP® properties.

Delamination mechanism of thermal barrier coatings induced by thermal cycling and growth stresses

The growth of thermally grown oxide (TGO) is often regarded as a key factor causing failures of thermal barrier coatings (TBCs) because it leads to thermal cycling and growth stresses. However, the delamination mechanism of TBCs induced by the growth process of TGO is still unclear. Here, a finite element method (FEM) considering both thermal cycling and growth stresses is developed. The accumulation of damage and crack nucleation, propagation, and coalescence are obtained using a phase field damage model. The results indicate that there is a critical TGO thickness of 8–10 μm, which may result in delamination of the TBCs. Both thermal cycling and growth stresses induce the premature failure of TBCs. The delamination mechanism induced by thermal cycling and growth stresses is obtained. When the interface roughness is A/L ≥ 1/4, the cracks pass through the TGO/TC interface and propagate in the TC layer. When the interface roughness is A/L ≤ 1/8, the cracks propagate along the vicinity of the TGO and will not pass through the TC/TGO interface. When the interface roughness is 1/8 < A/L less than 1/4, the cracks bifurcate at the vicinity of TGO interface, and one branch propagates in the TC and the other propagates along the vicinity of the TGO.

Reliability of Cu Nanoparticles/Bi-Sn Solder Hybrid Bonding Under Cyclic Thermal Stresses

The influence of thermal cycle stress loading on hybrid bonding, which was formed by sintering a mixture of Cu nanoparticles and a eutectic Bi-Sn solder powder, has been investigated. A Si chip and a directly bonded aluminum (DBA) substrate were bonded using the hybrid bonding layer. The bonded sample was evaluated using a thermal cycle test (− 40°C and 250°C). The degradation process of the sample during the test was observed nondestructively using synchrotron radiation x-ray computed laminography. The thermal cycle stress loading had a minimal effect on the microstructure of the bonding layer, which has a high bonding strength owing to the liquid phase sintering and high decomposition melting temperature of the Cu-Sn compound formation. This property reduced the Al deformation of the DBA substrate caused by the thermal cycle loading, resulting in the suppression of the bonding layer degradation. Therefore, hybrid bonding can be instrumental in achieving the reliable operation of power modules at high temperatures.

Numerical investigation of thermo-mechanical properties for disc brake using light commercial vehicle

A brake is a device using which frictional resistance is applied for stopping a moving vehicle. In disc brakes, the component on which the pads are squeezed when the brake pedal is applied. Disc brakes are subjected to both mechanical and thermal stresses. The cyclic thermal stress is more significant than mechanical stress. In this study, three-disc brakes with different profiles are selected to investigate the thermo-mechanical behavior analytically and numerically. This analysis develops a three-dimensional (3D) thermo-structural coupling model, implements transient thermal Analysis and transient structural Analysis of disc brake profiles with a frictional heat. The thermo-structural problem is solved by the finite element method to get the transient temperature and thermal stress fields of the disc brake under emergency braking. Comparison between the three profiles has been made using different parameters, including the maximum temperature on the surface, equivalent thermal stress (Von-Mises), and thermal deformation. The result has shown that the having grooved profile on its surface exhibited 34Mpa of equivalent stress, whereas the solid type and the drilled type have shown 80Mpa and 57Mpa. It also shows that the grooved type brake is efficient by far more magnitude than the other two profiles. In general, the thermal stress developed and thermal deformation on the would significantly decrease when it has a profile that allows for better heat dissipation to the surrounding.

Simulation on Thermal Stress Cycle in Laser Cladding of H13 Steel Ni-Based Coating

Simulation on Thermal Stress Cycle in Laser Cladding of H13 Steel Ni-Based Coating

Investigating the conjugate heat transfer phenomena on various ducts for aircraft environmental control system

All commercial aircraft employ a system called Environmental control system (ECS) to ensure an environment that accomplishes the physiological and comfort demands by passengers and aircrew. This task requires functionalities like temperature control, humidity regulation apart from the governing of cabin pressure. The energy source for ECS is a pressurized hot air bleed (180 °C-250 °C, 2.75 bar) from the engine or Auxiliary Power Unit (APU) along with the ram air. During the functional operation, the unit of Heating, Ventilation, and Air Conditioning (HVAC) duct experiences repetitive temperature fluctuations in addition to the cyclic pressurization leading to thermal fatigue and cyclic stress over the duct material, promoting crack propagation at weld zones in the duct. Therefore, a comparative investigation on conjugate heat transfer analysis is done at welded joints annexed to the bypass valve and trim air valve using airflow bench set up and validated by computational fluid dynamics. During this investigation, the circular duct with spherical junction (D/d = 3.84 & L/d = 6) was the most efficient and economical design that could fit in for designing air conditioning duct undergoing high thermo-cyclic stress.

Effect of laser polishing on the microstructure and mechanical properties of stainless steel 316L fabricated by laser powder bed fusion

While metal additive manufacturing has seen significant growth in recent years, the surfaces produced often need post-processing to improve surface finish, mitigate residual stresses, and remove surface-connected porosity. Laser polishing, by means of remelting a thin layer of the surface, is one post-processing method being investigated for surface finish improvements and other surface enhancements. In this work, the surface morphology and microstructure of laser powder bed fused (L-PBF) stainless-steel 316 L (316 L) before and after laser polishing are characterized by optical microscopy (OM), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscopy (TEM). In addition, the cross-sectional microhardness of the samples is measured and reported. Additionally, the as-built and laser-polished sample's tensile properties are characterized using uniaxial tension tests. The results indicate that the surface roughness of as-built 316 L (Sa = 4.84 μm) can be substantially reduced through laser polishing (Sa = 0.65 μm). After laser polishing, the average grain diameter is reduced and the proportion of low angle grain boundaries (2°~5°) is increased in the L-PBF 316 L. The maximum sub-surface hardness reaches 262 HV, and both the tensile strength and ductility of 316 L are increased after laser polishing. This enhancement is attributed to thermal cycling stresses, grain refinement, the elimination of surface defects, and dislocation strengthening after laser polishing.

Development of Highly-Sensitive and Reliable Fiber Bragg Grating Temperature Sensors With Gradient Metallic Coatings for Cryogenic Temperature Applications

Temperature monitoring is an essential task in cryogenic engineering to ensure the safety of equipment, where highly sensitive and reliable sensors are required to provide real-time and accurate information about temperature. Titanium (Ti)-copper (Cu)-coated fiber Bragg grating (FBG) temperature sensors with a gradient of material properties to minimize thermal stresses are hence fabricated by a combination of Ti/Cu magnetron sputtering and Cu electroplating. The thermal characteristics and thermal fatigue behavior of the sensors are investigated. The sensors exhibit significantly higher sensitivity than that of the bare FBGs at cryogenic temperatures down to 79 K, with good repeatability and stability. Their response to the temperature changes can be precisely described by a quadratic-polynomial equation. No obvious variations in the zero-point, the reflection spectrum, and the temperature sensitivity of the sensors exposed to thermal fatigue from 77 K to room temperature are observed before fatigue failure which could be attributed to the formation and growth of subcritical cracks within the fiber rather than that of fatigue cracks within the metallic coatings, as a result of the cyclic thermal stresses induced by the large differences in coefficient of thermal expansion between the silica optical fiber and the metallic coating materials. The results demonstrate that the multilayer metal-coated FBG sensors provide great potential for temperature measurements or temperature compensation in cryogenic engineering by proper selection of metallic coatings with a gradient of material properties.

The effect of TiO2 buffer layer thickness on the thermochromic properties of VO2 thin-film fabricated by high density plasma source

Thermochromic VO2 thin films are fabricated by using high power impulse magnetron sputtering at room temperature. In order to increase the crystallinity and transparency of VO2 thin films, a barrier layer of TiO2 is deposited on the glass substrate. Then TiO2/VO2 stacks are post-annealed at a temperature of 500 °C for 3 min. The transmittance properties as functions of TiO2 and VO2 thicknesses are discussed. The effects of TiO2 thickness on the strain state of (011) and () planes of monoclinic phase are studied. The laminated film shows satisfactory optical properties with an excellent solar regulation efficiency (ΔTsol = 10.2%) and an acceptable luminous transmittance (Tlum = 41.1%) in a low-temperature state. Good endurance property is demonstrated using a thermal stress cycle of 25 °C/85 °C for 100 times.

Potential applications for perovskite solar cells in space

Abstract Perovskite solar cells (PSCs) have drawn significant attention because of high power conversion efficiency, solution processability, large-area device fabrication and low cost. Recently, PSCs have been considered as a promising candidate for the power source of the spacecrafts and satellites in space missions due to their high specific power and cosmic radiation resistance. Herein, we review the main challenges for achieving space-grade perovskite solar cells: light instability, thermal cycling stress and high vacuum-induced issues, as well as the technical advantages with respect to ultra-lightweight, radiation tolerance and upscaling potential. Finally, an outlook on the future development is presented.

Investigation of solar cell degradation using electrochemical impedance spectroscopy

The performance of solar cells reduces annually due to various unavoidable phenomena of thermal cycling, damp heat, UV exposure, and mechanical stress, etc. Generally, I-V characteristic is used to check the performance of the solar cell, but the minor stress conditions mentioned above are difficult to characterize by I-V measurement. Impedance spectroscopy is a widely used method in fuel cell and a battery that can be used to detect minor degradation in the solar cell by analyzing the change in equivalent circuit parameters. In this work, commercially available polycrystalline silicon solar cell is investigated under the condition of hotspot, mechanical stress, and disconnection of interconnection ribbon and then characterized by impedance measurement, Fourier transform (Bode plot) as well as I-V characteristic. The results show noteworthy decrease in parallel resistance (Rp) which is clearly visible in Nyquist plot in compare to the I-V characteristic. The Rp decreases in EIS from 283.60 to 234.80 Ω for mechanical stress test, from 273.0 to 187.10 Ω for hotspot and from 352.80 to 345.20 Ω for disconnection of interconnection ribbon test. The results confirm potential application of impedance measurement for solar cell characterization due to noteworthy change in equivalent circuit parameters after test conditions.

A method to account for transient performance requirements in the design of steam generators for concentrated solar power applications

Concentrating solar power plants are strongly characterized by recurring start-up and shut-down procedures. This imposes new challenges for conventional components such as the steam generator systems, as frequent load variations might lead to high thermal stress cycles, affecting their lifetime negatively. In this context, the header and coil design is a favourable configuration to reduce stresses. This paper introduces a method to design the heat exchangers of the header and coil steam generator type accounting for the dynamic performance, thermal stress sensitivity and impact on the performance of the power plant. Optimal designs were determined by minimizing the cost and total water-side pressure drop of the steam generator and the levelized cost of electricity of the power plant. The steam generator dynamic model was successfully validated using operational data. The results suggest that a steam generator design characterized by a tube outer diameter of 30 mm, high steam generator pressure drop and low investment cost is the optimal solution for the power plant under consideration. A configuration featuring a large number of tube layers is optimal in order to reduce the pressure drop at the superheater while at the same time, guaranteeing acceptable stresses and good transient response.

Fracture behavior of tungsten-based composites exposed to steady-state/transient hydrogen plasma

The fracture behavior of plasma-facing components (PFCs) under extreme plasma-material interaction conditions is of great concern to ITER and future fusion reactors. This was explored in the current study by exposing pure tungsten (W), W-1%TiC and W-2%Y2O3 composites to a combined steady-state/transient hydrogen plasma up to a base surface temperature of ~2220 K, and up to 5000 transient pulses for 1000 s using the linear plasma generator Magnum-PSI. The applied heat loads were characterized by combining sheath physics, thermographic information and finite element analyses, with which the thermal stress was evaluated. Combining microstructural investigation and thermo-mechanical numerical analyses, a physical picture of fracture is developed. The transient heat loads drive surface crack initiation, whose depth can be estimated by a simple analytical model for pure tungsten, while the cooling period following the steady-state heat load induces tensile stresses, opening existing surface cracks deeper. The fracture process is mediated by the microstructure whereby the ceramic particles stabilize the microstructure but promote surface crack initiation due to suppressed plasticity at the grain boundaries and the particle-matrix interfaces. The surface cracks relieve the subsequent cycles of transient thermal stress but intensify the steady-state thermal stress, therefore, promoting deep crack propagation. These results help to understand failure mechanisms in PFCs under extreme operation conditions which are valuable for developing advanced PFCs.

Fatigue Properties for Bi-2212 High Temperature Superconducting Round Wires Under Axial Tensile Loading

Bi-2212 wires, which have high critical current density and critical magnetic field without anisotropy, offer significant potential applications for ultrahigh-field superconducting magnets. The Bi-2212 wire is very sensitive to strain. The strands are inevitably subjected to cyclic thermal or electromagnetic stress during application. There is a lack of understanding regarding the fatigue properties. In this paper, the degradation behavior of critical current for Bi-2212 wires under axial tensile fatigue loading was investigated. It was found that the fatigue life decreases with the increase in maximum fatigue stress.

Estimation of resource capabilities of the NPP turbine unit under the primary frequency control of the current in the power system

The purpose of the article is to estimate the life cycle on the example of NPP with the K-1000-60/1500 turbine and with the VVER-1000 reactor under cyclic load changes using the primary frequency control. The criterion for estimating the life cycle is the rate of the fatigue crack growth of the most loaded rotor element. The main requirements for the NPP power units under conditions of involvement in the primary frequency control are provided. The cyclic loading of the NPP turbine unit blades under conditions of maintaining the power reserve due to a reduction in the load by 2% by throttling the steam, and in line with the requirements for participation in the primary frequency control by 8% of the nominal capacity is substantiated. At the same time, the cyclic mechanical and thermal stresses are determined for the HPC and the LPC rotor blades. In this regard, it is shown that the first stage blades of the HPC rotor during unloading by 8% of the nominal capacity of the most cyclically loaded. The loading intensity and the rate of the fatigue crack growth of the first-stage blades of the HPC rotor are determined on the basis of the cyclic crack-resistance methodology and the Paris equation. It is shown that the rate of the fatigue cracks growth is negligible which determines their longterm life cycle.

Reliability Study of c-Si PV Module Mounted on a Concrete Slab by Thermal Cycling Using Electroluminescence Scanning: Application in Future Solar Roadways

Several tests were conducted to ratify the reliability and durability of the solar photovoltaic (PV) devices before deployment in the real field (non-ideal conditions). In the real field, the temperature of the PV modules was varied during the day and night. Nowadays, people have been bearing in mind the deployment of PV modules on concrete roads to make use of the space accessible on roads. In this regard, a comparative study on the failure and degradation behaviors of crystalline Si PV modules with and without a concrete slab was executed via a thermal cycling stress test. The impact of the concrete slab on the performance degradation of PV modules was evaluated. Electroluminescence (EL) results showed that the defect due to thermal cycling (TC) stress was reduced in the PV module with a concrete slab. The power loss due to the thermal cycling was reduced by approximately 1% using a concrete slab for 200 cycles. The Rsh value was reduced to approximately 91% and 71% after thermal cycling of 200 cycles for reference PV modules, respectively. The value of I0 was increased to approximately 3.1 and 2.9 times the initial value for the PV modules without and with concrete, respectively.

Comprehensive Numerical Simulation on Thermally Grown Oxide and Internal Stress Evolutions in Thermal Barrier Coatings

TBCs (Thermal Barrier Coatings) is deposited on gas turbine blades to protect the substrate from a combustion gas flow. One of the serious problems occurred in gas turbine is TBC delamination which is caused by startup, steady and stop operation in service. TBC delamination results from subjecting to both cyclic thermal stress and evolution of internal stress due to thermally grown oxide (TGO). In this study, the finite element code which can simulate thermal and internal stress fields generated in TBC was developed. The developed code involves the follows: inelastic constitutive equation for ceramic coating, bilinear-type constitutive equation for bond coating and Chaboche-type inelastic constitutive equation for the substrate, and mass transfer equation in consideration of oxygen diffusion and chemical reaction with aluminum. Thermal cycling simulation was conducted using the developed code. It was confirmed that maximum stress and its location in the ceramic coating/bond coating interface were matched with the associated experimental results.

Characterization of selected properties of WC–WB–Co and WC–FeCrAl coatings applied by HVOF technology

Abstract The paper presents results of the research focused on the characterization of two types of coatings – WC–FeCrAl and WC–WB–Co. The properties of the WC–FeCrAl coating (Co and Ni free) were compared against the WC–WB–Co coating to see if it could be used as an environmentally more suitable substitute for conventional Co and Ni containing powders. The coatings were applied by HVOF technology. The influence of thermal cyclic stress on the hardness, adhesion of coatings and their corrosion resistance was determined. A change in the phase composition of coatings after thermal cyclic loading was also determined.

An evaluation of the reduction of heat loss enabled by halloysite modification of oilwell cement

The increasing reliance on steam-assisted gravity drainage (SAGD) to access unconventional bitumen deposits within the sub-Arctic necessitates the development of robust cement sheaths for oilwell cementing. Such cement sheaths can potentially increase the energy efficiency of the SAGD process by reducing heat loss while maintaining mechanical integrity upon prolonged exposure to cyclic thermal stress. Modifying oilwell cement by the inclusion of hydroxyethylcellulose-functionalized halloysite nanotubes (HEC-HNTs) within the cementitious matrix results in a high density of enclosed void space and disparate interfaces, which serve to scatter phonons and reduce thermal conductivity. In this study, we have systematically evaluated the influence of HEC-HNT loading on the thermomechanical properties of cement with and without the addition of calcium chloride as an accelerator and have correlated the reduction of thermal conductivity to the distinctive microstructure of the nanocomposite cement. The incorporation of HEC-HNTs in thermal cement reduces the thermal conductivity from 0.856 W m−1·K−1 to 0.206 W m−1·K−1 without substantially altering the compressive strength. Model systems mimicking SAGD oilwell cement sheaths have been prepared from umodified and modified (incorporating HEC-HNT) cement and subjected to cyclic thermal stress emulative of SAGD conditions. Cement sheaths constructed from the modified cement with CaCl2 maintain a higher temperature gradient as compared to unmodified cement with CaCl2; a 12 °C increased temperature differential between hot and cold surfaces is observed for a 4.5 cm thick sheath with a considerably shallower rate of increase in temperature. Aggressive thermal cycling (20 h at 250 °C followed by 4 h at 25 °C) for 20 days brings about a 20% reduction of compressive strength. The combination of additives facilitating thermal insulation and mitigating differential shrinkage provides an attractive means of oilwell cementing for SAGD applications wherein cyclic thermal stresses are operational and energy efficiency is of paramount importance. Extrapolating the considerably increased temperature differentials between hot and cold ends within model systems to entire wells portends significant energy savings and reduction in amounts of injected steam.