Cyclic Thermal Stress Research Articles

Study of electrical fatigue test in gold-coated siliver-4 wt.% palladium bonding wire

Present study investigates the effects of the electrical fatigue test on the microstructures, electrical properties and elemental distribution of gold (Au)-coated Ag-4Pd (ACA4P) alloy wire. The electrical fatigue test is an important method for estimating the reliability of electronic devices to cyclic thermal stress caused by bias-induced Joule heat. In the bias test, the thermal diffusion behavior of Au atoms on the wire surface was more intense with increasing current density. The Au atoms diffused along the grain boundary of the wire and finally distributed throughout the wire matrix. In the bias fatigue test, the electrical resistances of the wire and ball bond decreased, and then increased as the bias cycle increased to 6000 cycles. An increase in grain size of the wire and ball bonded wires by bias-induced thermal energy caused their electrical resistances to decrease. Poisson's effect caused the diameter of the wire to decrease, and thus increased the resistance of the wire. The growth of Ag2Al intermetallic compounds (IMCs) at the bonding interface was responsible for the increase in the resistance of the ball bonded wire.

Reliability of printed wire bonds

Abstract Additive manufacturing is an emerging domain with numerous potential applications. The concept of those new processes offers many advantages such as design flexibility, truly 3D packages and low cost for customization. The aerosol jet printing could enable wire bonding-like techniques that are unachievable with round wires today, combined with serious advantages for high frequency applications. However, this new field is starting off with many challenges to address, with the reliability as a focal point. The focus of this study is the reliability of printed wire bonds. Polyimide and silver inks were printed using an aerosol jet system (OPTOMEC Aerosol Jet ® HD Decathlon™). The results are focusing on the reliability of the adhesion of polyimide ink (UTD-PI-AJ) in an ethanol-based diluent and a silver ink, the HPS-108AE1 from Novacentrix, on different surface types: silicon oxide, pure aluminum and gold (ENIG). The adhesion is first addressed by a qualitative tape test at room temperature. The test samples are then put into an environmental chamber for a Deep Thermal Cycling (DTC) stress. The samples cycled 1000 times between −20°C and 85°C. They were inspected for physical defects at 250, 500 and 750 cycles. The visual inspection for defects focuses on cracks and delamination. The printed wire bonds were simulated by printing polyimide ink into a gold plated flat ceramic substrate (28 LCC from Kyocera) and then printing conductive silver ink from opposite pin leads. A layer of polyimide ink was then added on top of the printed lines. Crossover lines were finally printed on top of the last polyimide layer, again from opposite pin leads, creating an array of superimposed printed wire bonds. The reliability of printed wire bonds is tested through a Highly Accelerated Stress Test (HAST, 110°C, 85%RH, 264h) under bias. The samples were inspected at 66h, 132h and 198h for visual defects such as cracks, delamination and silver electro-migration. Cross-sections were performed on samples before and after HAST. All defects were characterized regarding of their time and condition or appearance and of their dimensions.

A Comprehensive Analysis of Premature Failure in a Cobalt-Based Superalloy X-45 Gas Turbine Vane

The main objective of the current investigation is to determine numerically and experimentally the failure mechanisms of a cobalt-based superalloy X-45 used as a gas turbine vane. A numerical study was performed through the finite element method using ABAQUS software to determine temperature distribution as well as thermal stress induced by the thermal gradient in the vane segments. In addition, experimental studies were performed to study the effect of service-induced microstructural changes in the vane body through optical microscopy and also scanning electron microscopy. Furthermore, microhardness of the specimen was carried out to determine the effect of thermal stress on different zones of the vane. Finally, it was found that the vane was failed as a result of different failure mechanisms including cyclic thermal stress, oxidation, high-temperature corrosion and more importantly phases transition of primary carbides (M6C) to secondary ones (M23C6), due to high-temperature operations.

Novel Waveforms, Models, Algorithms for Cable Health Monitoring

Cables in power generation and delivery are under high thermal stress cycles. Such high temperature can lead to cable insulation degradation, which will reduce the projected lifetime. Existing methods mainly focus on cable fault detection or insulation degradation mechanism. There is no existing tools for diagnosing the insulation degradation level and predicting the remaining useful life of the cable. The goal of my Ph.D. research is to develop reflectometry and data based approaches to monitor the health status of cables. The research will be conducted in three steps: (1) development of reflectometry based method to monitor the cable insulation degradation; (2) feature extraction and cable insulation degradation dynamic modeling based on the accelerated aging test data; (3) development of risksenstive particle filtering based fault diagnosis and prognosis algorithms for cable degradation; and (4) verification and validation the proposed solution with new experiment data and comparison with existing approaches.

Mechanical Reliability of Photovoltaic Cells under Cyclic Thermal Loading

Metallic coatings placed on solar cell should retain their structural integrity over the life-span of the devices in order to ensure their reliable functioning. One critical component of such a life-assessment exercise is based on their response to the cyclic thermal stresses generated due to the temperature fluctuation, which is inevitable during regular operation of a solar cell and the difference in the thermal expansion coefficients of metal coatings and Si. Here, we have studied the impact of accelerated thermal cycling on the integrity of the semiconductor–metal layer in a commercial monocrystalline Si based photovoltaic solar cell comprising Ag finger-lining and Al backside coating. We observed that, compared to Si-Ag interface, the Al-Si interface was significantly weaker, wherein cracks easily nucleated and grew during thermal cycling between − 40°C and 90°C. The experimental results were augmented with finite element method (FEM), including extended-FEM (XFEM), simulations using geometry based on the actual microstructure of various metal-Si interfaces in the solar cell module. FEM-based simulations suggest excessive stress concentration at the interface of Al-Si eutectic-Al layers due to the irregular wavy nature of this interface. XFEM results indicate the critical role of the interfacial adhesion strength and roughness of the eutectic-Al interface on the crack growth and its propagation path. Based on the obtained results, a discussion on the fabrication of solar cell modules resistant to thermal stress induced structural damage is presented.

A Backpropagation Neural Network-based Flexural-tensile Strength Prediction Model for Asphalt Mixture in Cold Regions under Cyclic Thermal Stress

A Backpropagation Neural Network-based Flexural-tensile Strength Prediction Model for Asphalt Mixture in Cold Regions under Cyclic Thermal Stress

Study of rollers thermal state at hot rolling of long products profiles at 370/150 mill of OJSC “Belorussky steel-works – UKKh “Belorusskaya metallurgical company”

In the rolling production, rolls with box passes are widely used, which is explained by the best gripping ability and high draw ratio. However, along with these advantages, there are significant drawbacks - the formation of an erosion net along the bottom of the pass and side cracks on the side outlets, since hot rolling of metals and alloys is accompanied by intense wear of the working rollers and welding fixtures, which happens due to exposure to high temperatures and stresses. Therefore, the task of elaboration of rational temperature regime to provide not only stable mill operation, but also high rollers endurance, is rather actual and requires its solution. It is very important to follow the today’s trend to increase continuous mills rolling speed, which will result in still heavier temperature conditions of rollers operation. Results of the study of the rolling process main technological parameters influence on the formation of erosion net across the bottom of the pass presented, as well as magnitude and nature of the distribution of thermal cyclic stresses along the surface layers of the bottom of pass. Study of the thermal state of roughing stands rollers of OJSC “Belorussky steel-works” 370/150 continuous wire-rod mill show, that comparing with intermediate and finished stands rollers they subject more to thermo-cyclic destruction of passes surface, but not to mechanical one. As a result of the computer simulation new data obtained on the character and peculiarities of dynamics of surface thermal state of rollers passes. The possibilities to reduce thermal cyclic stresses by improving the cooling regime of the rolls shown. Using the simulation by the finite elements method, the study of the dynamics of heating and stress state of the surface and subsurface layers of the pass bottom was accomplished. Based on the analysis results of numerical experiments and analytical calculations, isotherms of the surface layers of the bottom of the pass were compiled to select the optimal cooling mode. The data obtained can be used to control the cooling systems of roughing stands rollers of continuous section and pipe hot rolling mills.

Low thermal budget annealing for thermochromic VO2 thin films prepared by high power impulse magnetron sputtering

Thermochomic 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, first a buffer 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 as functions of film thickness and O2/Ar ratio during film deposition is discussed. It is found that the O/V atomic ratio decreases with increasing O2/Ar ratio, which is due to serious inter-diffusion inside stacked layers. At high O2/Ar ratio, columnar-shaped crystals are suggested, which belongs to V2Ti3O9:Si quaternary oxide. The depth profiles of binding energies measured by X-ray photoelectron spectroscopy are compared with different O2/Ar ratios. Good endurance property for a thermal stress cycle of 25 °C/85 °C is obtained under the O2/Ar ratio of 6%. The laminated film shows satisfactory optical properties with an excellent solar regulation efficiency (ΔTsol = 10.4%) and an applicable luminous transmittance (Tlum = 35.2%) in a low-temperature state.

Evolution of cyclic thermal stress in selective laser melting of 316L stainless steel: a realistic numerical study with experimental verification

It is well known that high thermal stresses in the formed parts during selective laser melting (SLM) heavily affect the part quality and performance. In this study, the mechanism of thermal stress formation due to temperature gradients in SLM of 316L stainless steel is investigated. The uniqueness of this study lies in the fact that a realistic multi-track and multi-layer SLM process is modeled and simulated that adopts the identical conditions of the actual part building on a commercial SLM system, and the final residual stresses are compared between the simulation and the experimental measurements on the actual parts. The results indicate that both temperature and stress evolution of material points exhibit cyclic patterns during the SLM process, and the changes with regard to time are dramatic thanks to the rapid heating and cooling of localized areas. However, the rapid temperature decrease is actually accompanied by stress increase in the material points, and vice versa. Under the laser power of 160 W and scanning speed of 500 mm/s, a melting pool is formed and rapidly expanded to the adjacent pre-solidified layer, and the diffusion depth is about 200 μm. Also, unlike the overall attenuation of temperature as the SLM build process progresses, the magnitude of stress oscillation actually increases. Furthermore, during the rapid solidification, the core of melting pool is subject to tensile stress. The tensile stress could be partially mitigated by the laser heating of subsequent layers, but it cannot be completely removed. As a result, the accumulation effect of multiple layers leads to significant tensile stress, in particular, in the bottom layers that are closer to the base plate. The effective stress in the bottom layer attached to the base plate reaches as high as 680 MPa based on the settings of SLM process. Finally, the experiment measurement on residual stress overall agrees with the simulation results. Both show that the residual stress ranges from 100 to 350 MPa for the layers 1.4 mm above the base plate, and that the tensile stress tends to increase along the direction towards the base plate.

Thermal Diffusion Phenomena of the Functional Polymer Lubricants for the Heat-Assisted Magnetic Recording

Materials in a newly designed head–disk interface in the heat-assisted magnetic recording (HAMR) have to satisfy harsh operating conditions including cyclic thermal stresses generating large thermal gradient where the heated lubricants evaporate as well as thermally flow-out. Therefore, the stumbling block in the HAMR technology is to fully understand the system behavior under large thermal effects on the lubricant diffusion related to the depletion in the heated zone. The previous studies have investigated local thermal diffusion, depletion, and recovery phenomena of nonfunctional perfluoropolyether lubricant by studying the lubricant behavior at the center and the formation of a rim at the edge of heated zone, while the diffusion mechanism in the heated area has not been fully understood. In this paper, we examined the thermal effects on the lubricants for the application of HAMR in two aspects: 1) thermal diffusion for the replenishment and 2) lubricant evaporation for the loss of the lubricant by using the molecular dynamics.

Failure Analysis of Liner Plates of Wet Coke Quenching Car

Quenching of coke after carbonization is an important step that influences its strength and reducibility in a blast furnace. During the wet coke quenching process, hot coke from 1200 °C is brought down to a temperature of around 100–150 °C by impingement with jets of water. It was observed that the liners of quenching car buckets would fail during service in 15 days to 1 month. Chemical analysis revealed the failed liners were made of heat resistant HK 40 cast alloy. Multiple cracks were observed to have initiated from the surface and propagated through the material. Microscopic analysis showed crack branching with inter-dendritic propagation. Furthermore, WDS elemental mapping revealed that there was a significant concentration of S and Cl with marked decrease in concentration of Cr preferentially along the crack propagation paths. These suggest that stress corrosion cracking (SCC) is the primary mode of failure. Thermal stresses during sudden quenching of coke can be attributed to provide the stress needed for SCC. It appears that the mechanism of SCC is lowering in energy required for crack propagation in the presence of certain environment and alloy combination. Cyclic thermal stress reversals and difference in coefficient of thermal expansions of carbides and austenite leading to thermal stresses would have contributed to the failures. A ferritic-pearlitic steel liner which is not susceptible to SCC in the working environment was recommended, and it enhanced the service life by at least 400%.

High temperature shape memory behavior of Ni47.3Ti29.7Hf20Pd3 alloys

The shape memory properties of Ni47.3Ti29.7Hf20Pd3 alloys were investigated through stress-free thermal cycling, constant-stress thermal cycling and constant-temperature stress cycling experiments. The alloys showed reversible phase transformations above 180 °C, which makes them suitable for high temperature shape memory applications. Constant-stress thermal cycling experiments revealed that recoverable strains of about 2% were possible under compressive stress levels higher than 700 MPa and both the recoverable strain and thermal hysteresis values were strong functions of applied stress. Additionally, two-way shape memory strain of 0.7% was observed. Unlike most of the shape memory alloys that have Class I transformation, Class II transformation was observed in these alloys and its relationship to the elastic energy storage was discussed through thermo-elastic martensitic transformation thermodynamics approach.

Modeling Thermomechanical Stress with H13 Tool Steel Material Response for Rolling Die under Hot Milling

For the extreme pressure and temperature arising in the hot rolling process, thermomechanical (TM) models are used to predict the residual stresses on the surface of the die because a quantification of the TM stresses allows a prediction of the life span of the rolling die. As the accuracy and consistency of models developed in this area show a large variation due to the considered parameters, conditions, and assumptions, the capability of the developed models needs to be verified for a particular set of circumstances. In this study, new constitutive equations are proposed and a model consisting of five sub-models that computes temperature distribution, thermal stresses, mechanical stresses, and thermomechanical stress for the rolling die under continuous casting application has been developed and presented in this paper. The first sub-model describes the temperature distribution on the rolling die surface by accounting for the effects of different process parameters such as the initial temperature of the slab, reduction ratio, and the rolling speed, while the second and the third sub-models describe the thermal cyclic stress and the elasticity deformation of mechanical stress, respectively. Furthermore, the fourth sub-model describes the TM stress generation through inheriting numerical approaches, and the last sub-model is developed for the H13 tool material response at a high temperature. To verify the developed analytical models, a finite element simulation and the experimental data are considered. The analytical models are computed using Python, and the ABAQUS software has been used for the finite element simulations. The results show a good agreement with the finite element simulation and experimental data.

A multi-method monitoring of timing, magnitude and origin of rockfall activity in the Japanese Alps

A multi-method monitoring was conducted to detect the timing and trigger of rockfall activity on an alpine rockslide cliff composed of Cretaceous sandstone and shale in the southern Japanese Alps (Aresawa rockslide, 2900 m above sea level). The monitoring programme includes manual measurements of flaking from painted rock surface and collection of fallen debris, daily time-lapse imaging of the rockwall, automated recordings of rock temperature, rock moisture and influencing meteorological factors (air temperature and precipitation). A stereographic pair of sequential photographs is used to visually identify the location of new erosion and semi-quantitative evaluation of detached materials at daily resolution. Six years (2010–2016) of debris trapping show major rockfall activity in winter (between November and May) and occasional activity associated with heavy rains in summer, and yield an average rate of rockwall retreat on the order of 1 mm a−1. The rockwall shows heterogeneous debris production mainly reflecting joint spacing. Time-lapse imaging displays at least 10–15 rockfall events per year within the shot area (~500 m2). The integration of multiple data suggests at least five types of triggering processes towards rockfalls, which recur annually. (1) In summer and early autumn, heavy rainfalls raise the moisture content of the shallow bedrock, often triggering significant rockfalls, probably due to raised water pressure in rock joints or lubrication of joints. (2) In late autumn and late spring, light or intermediate rainfalls are sometimes followed by high moisture, shallow freezing, rapid thawing and eventually by different scales of rockfalls. (3) In winter and early spring, the same process as in the second case, but rainfall is replaced by snowfall, triggers submeter-scale rockfalls. (4) Deep seasonal freezing to about 5 m enables release of meter-scale rockfalls during seasonal thawing periods from late spring to early summer. (5) Short-term large thermal fluctuations that produce cyclic thermal stress may also contribute to submeter-scale rockfalls, mainly in winter locally enhanced by freeze-thaw action.

Thermal Stress and Cyclic Stress Analysis of a Vertical Water-Cooled Wall at a Utility Boiler under Flexible Operation

Supercritical once-through utility boilers are increasingly common in flexible operations in China. In this study, the tube temperature changes at a vertical water-cooled wall are analyzed during a fluctuating flexible operation. There are considerable differences in the temperatures of the parallel tubes at the minimum load, and the resulting thermal stress distributions at a front water-cooled wall are established using structural calculation software ANSYS 17.1, USA. A wide thermal stress distribution occurs among the parallel tubes, and the local cyclic stress amplitudes under flexible operation are higher than those under cold, warm, hot, or load-following operations. Because of the water wall expansion structure at the furnace, the higher tube temperature areas suffer from compressive stress, while the lower tube temperature areas suffer from tensile stress. During flexible operation, combustion uniformity and a two-phase flow distribution can improve the safety of vertical water-cooled wall operation. The minimum load of the utility boiler should be set as a limitation, and the tube temperature is an important parameter affecting the thermal and cyclic stresses.

EFFECT OF HIGH-CURRENT ELECTRON BEAM IRRADIATION ON RESISTANCE OF SULFIDE-OXIDE CORROSION OF NI-CR-AL-Y ION-PLASMA COATINGS

Recently, the emergence of accelerators of high-current electron beams and powerful electron ion beams has contributed to the creation of unique effects of concentrated energy flows on materials. Upgrading of production processes and development of new technological processes of both domestic aircraft propulsion engineering and aviation arms remain topical and needed. Engine operational reliability depends on that of turbine blades. They are the most loaded details because they are experienced to action of static, dynamic and cyclic loadings as well as are subjected to cyclic thermal stresses. Therefore the main objective of our paper is to analyze the effect of high-current electron beam irradiation on-resistance of sulfide-oxide corrosion (SOC)of Ni-Cr-Al-Yion-plasma coatings. To achieve this purpose, beam irradiation was performed using the RITM-SP complex automated electron-beam setup. Modification of surface layer of SDP 2+VSDP16 ion-plasma coating by microsecond high-current electron beams of selected mode made it possible to increase considerably the SOC resistance. An analysis of the surface and microstructure of samples after SOC testing enabled to determine different effects of medium on sample coating depending on the state of the sample surface. When investigated samples microstructure, we found that after modification certain cracks on sample surface did not develop in the course of testing. It was found that some craters were not necessarily centers of corrosion damage origin, i.e., the existence of given types of craters and their impact on SOC resistance stability are ambiguous.

Study on welding thermal cycle and residual stress of UNS S32304 duplex stainless steel selected as external shield for a transport packaging of Mo-99

Thin plates of duplex stainless steel UNS S32304 were welded using the pulsed gas tungsten arc GTAW process (butt joint) without filler addition. The used shielding gas was pure argon and 98% argon plus 2% of nitrogen. The thermal cycles were acquired during welding, in regions near the melting pool. This alloy is candidate for the external clad of a cask for the transport of high activity radiopharmaceuticals substances. For the residual stress measurements in austenite phase an X-ray diffractometer was used in a Bragg-Brentano geometry with CuKα radiation (λ= 0.154 nm) and for ferrite phase was used a pseudo-parallel geometry with CrKα radiation (λ= 0.2291nm). The results of residual stress using sin2y methodology shown that the influence of the high welding temperature leads to compressive stresses for both phase of the duplex steels mainly in heat-affected zone. It was observed a high temperature peak and an increase of the mean residual stress after addition of nitrogen to the argon shielding gas.

Bond durability of CFRP laminates-to-steel joints subjected to freeze-thaw

The degradation mechanisms of bonded joints between CFRP laminates and steel substrates under severe environmental conditions require more durability data and studies to increase the database and better understand their causes. Studies on bond properties of double-strap CFRP-to-steel bonded joints with two different composite materials as well as adhesive coupons subjected to freeze-thaw cycles for 10,000 h were conducted to reduce that gap. In addition, the equivalent to the number of thermal cycles and their slips induced in the CFRP laminates was replicated by an equivalent (mechanical) loading-unloading history condition imposed by a static tensile machine. The mechanical properties of the adhesive coupons and the strength capacity of the bonded joints were only slightly changed by the artificial aging. It was confirmed that the interfacial bond strength between CFRP and adhesive is critically related to the maximum shear stress and failure mode. The interfacial bond strength between adhesive and steel degraded with the aging. However, the equivalent thermal cyclic bond stress caused no detectable damage on the bond because only the interfacial elastic regime was actually mobilized, which confirmed that pure thermal cycles aging, per se, at the level imposed, have a low impact on the degradation of CFRP-to-steel bonded joints.

Microscopic damage behavior in carbon fiber reinforced plastic laminates for a high accuracy antenna in a satellite under cyclic thermal loading

For a high accuracy antenna in next radio astronomy satellite, a candidate material is carbon fiber reinforced plastics (CFRP), because negative longitudinal coefficient of thermal expansion (CTE) for unidirectional CFRP enables a laminate with 0 CTE through appropriate laminate design. This enables high structural accuracy under large temperature fluctuation like space. On the other hand, when the laminate is subjected to thermal cycles, cyclic thermal stress occurs and causes microscopic damages. In this study, we characterized damage progress in CFRP laminates and resultant variation in mechanical properties under cyclic thermal loading. Three types of matrices, such as polycyanate ester, polyimide and epoxy resin were used to prepare CFRP laminates. Specimens were subjected to thermal cycles from −197°C to 120°C. The test was periodically stopped for surface observation and flexural loading. Transverse cracks in 90° plies accumulated with thermal cycles, whereas flexural modulus remained constant. We also numerically evaluated temperature gradient and resultant thermal stress distribution during cooling by finite element analysis. The result indicates higher transverse stress appeared in the surface of the specimen and saturated to constant value which corresponded with the value calculated based on classical lamination theory.

English

The main objective of this research is to estimate the critical temperature for triple-walled carbon nanotubes (CNTs)/epoxy resin. Critical temperature in this study is the temperature that inter-laminar shear stress in interfaces of triple-walled CNTs and epoxy resin is the maximum value. At maximum inter-laminar shear stress, the stress concentration between triple-walled CNTs and epoxy resin is the maximum. This phenomenon may cause crack initiation, propagation and fracture in fibers/matrix interfaces. In the presented study, this temperature is derived by applying analytical method. The results of this research showed that maximum inter-laminar shear stress could occur at 85°C, which appears to be the critical temperature. The results of this research could be applied in any industry dealing with thermal stress and thermal cycles. Key words: Critical temperature, triple-walled carbon nanotube (CNT), nanocomposites, thermal analysis, inter-laminar shear stress, coefficient of thermal expansion.