Accumulation Of Thermal Stress Research Articles

Analytical solutions for temperature and thermal-stress modeling of solid material induced by repetitive pulse laser irradiation

In this paper, heat conduction and thermo-elasticity models of repetitive pulse laser irradiation are established, and analytical solutions for temperature and thermal-stress of solid material induced by repetitive pulse laser irradiation are obtained using integral transform method. Temperature and thermal-stress distributions of solid silicon material for different parameters are given. Results show that, when the silicon irradiated by a repetitive pulse laser, temperature and thermal-stress accumulation effects will occur on the surface and inside the material. Temperature and thermal-stress rise in the laser irradiating cycle time and decrease in the cooling cycle time. In the thin layer of silicon surface vicinity, temperature and thermal-stress rise due to absorption of irradiated energy dominates over the conduction energy transport from surface to vicinity. As the depth increases, the absorption decreases, whereas the conduction enhances. The results of this study can give some theoretical basis for revealing the mechanism of repetitive pulse laser irradiation and provide some guidance for experiments of repetitive pulse laser irradiation in the next work.

A Pooled Analysis of Heat-Resistant Cr-Al Steels

Background . Under the conditions of rapid heating-cooling, nonuniform temperature fields occur in the volume of the part that contribute to the accumulation of thermal stresses. Such stresses may exceed the yield point of the alloy and destroy part’s material. The form of parts’ destruction depends on the properties of metal and operating conditions. A typical form of destruction is cracking. It was determined by the analysis of operation of thermal-resistant parts that the choice of alloy with high oxidation resistance is necessary, but not enough to provide the specified life of thermal-resistant items, since in thermal cycling conditions heat resistance of metal begins to appear primarily. Objective. The aim of the work is to establish the effect of carbon and rare earth metals on heat resistance of thermal-resistant Cr-Al steels for work in extreme conditions and the study of the kinetics and mechanism of destruction of metal. Methods. Samples of90 mm in length and12 mm in diameter were subjected to heat treatment in a box furnace to 1100 °C, and chilled under running water. Assessment of heat resistance was done with the appearance of thermal fatigue cracks on the side surface or at their ends. Phase composition and structure were investigated by modern X-ray diffraction and metallographic methods. Results. The mechanism and kinetics of the destruction of cast metal under conditions of thermal cycles were determined. The selection of Cr-Al steel for work under extreme conditions should be made with regard to its mechanical, physical, physico-chemical and technological properties, as well as the design features of a particular casting. Conclusions. To achieve high heat resistance in the conditions of high variable temperatures Cr-Al steel should comprise 25–30 % of Cr, 1.0–3.0 % of aluminum, 0.3–0.6 % of titanium, 0.2–0.4 % of C and 0 15–0.40 % of rare earth metals.

Modelling of Asphalt Mixes under Long Time Creep at Low Temperatures

Proper description of asphalt mixtures behavior under long time load is one of the most important factors in analyses of strain and stress relations at low temperatures both from traffic and environmental loads. For example different models of thermal stress accumulation require different approaches of description of asphalt concrete. But in all cases it is required to describe its behavior under long time loading, which in some cases may be even longer than 10 000seconds.This paper presents advantages and disadvantages of three different models used for description of the asphalt mixes behavior in low temperatures. The authors have chosen three following approaches: generalized models, which describe asphalt mixtures using one parameter – the stiffness modulus – designated for a specific temperature and time of loading; rheological models (represented by Burgers rheological model), which describe asphalt mixtures using two or more parameters at a discrete range of temperature but at a continuous range of time of loading and master curves models which describe asphalt mixtures in a continuous range of both temperature and time of loading.Parameters of presented models were obtained from laboratory three-point bending creep tests conducted on different asphalt mixtures: high modulus asphalt concretes (HMAC), conventional asphalt concretes (AC), stone matrix asphalt (SMA) and porous asphalt (PA). The bending creep tests were conducted at three temperatures: 0°C, -10°C and -20°C for the time of loading of 2400seconds according to the procedure developed at Gdansk University of Technology. In this study the authors presented parameters only for HMAC.Commonly used models assume that asphalt mixture is linear viscoelastic and thermorheologically simple material. Authors found that those assumptions were not always valid for long time loads at low temperatures, especially for asphalt mixes made with hard grade bitumen.As the conclusions the authors presented a comparison of parameters calculated for each analysed model, advantages and disadvantages of each model and the impact of a chosen model on asphalt pavement analyses at low temperatures.

Investigation of Thermal Stress In Different Metal Based Dental Restorations By Mathematical Analysis

Purpose: The aim of this study is to investigate the effect of heat changes in oral environment that produce thermal stresses (TS) in prosthetic restorations by mathematical method. Material and Methods: Three different metallic frameworks in gold alloy, commercial pure titanium (cpTi) and chrome-cobalt- molybdenum (CrCoMo) and the ceramics, Ticeramics for cpTi, Omega900 for CrCoMo and VM13 for Au alloys were used for mathematical modeling. The physical properties were obtained from the manufactures. The calculation method was based on Boley’s equation. Results: In ceramics the highest thermal stress was in Ticeramic and the lowest was in VM13. At interface of the restoration thermal stress accumulation was the highest in cpTi and Ticeramic and the lowest was in Au and VM13. In metallic substructures CrCoMo shows the highest and Au had the lowest thermal stress depositon in its structures. Conclusion: Thermal stresses are not cable off breaking the metal-ceramic bond strength but shorten the life span of the prosthetics. Key Words: Thermal stress, Dental materials, Ceramics, Titanium

The thermal-stress accumulation in anti-reflective coatings with multi-pulse laser irradiation

An analysis model is established to study the accumulation processes of temperature and stress in an anti-reflective coating with multi-pulse laser irradiation. Specifically, the influence of pulse interval on the thermal-stress accumulation effects is discussed in detail. Furthermore, the accumulations of temperature and stress dependence of pulse energy are discussed. The results show that stress has the same accumulation rules as temperature. The pulse interval has major impact on the accumulation process. When the time of pulse interval is close to the cooling time of material, the accumulation effect is not obvious. Furthermore, the accumulations of temperature and stress are more obvious with increasing pulse energy.

Retarding the Cu–Sn and Ag–Sn intermetallic compounds by applying Cu–xZn alloy on micro-bump in novel 3D-IC technologies

This study investigates the evolution of interfacial microstructures in Cu/Sn–3.5Ag/Cu and Cu/Sn–3.5Ag/Cu–15Zn (wt%) microbumps. Due to the small size of microbumps, Cu–Sn intermetallic compounds (IMCs) rapidly form from the Cu pads. These brittle IMCs occupy the entire joint and weaken joint reliability. Moreover, Ag3Sn tends to precipitate inside the solder in large plates, which results in the accumulation of thermal stress due to a CTE mismatch between Ag3Sn and β-Sn. It is demonstrated that doping Zn into one of the Cu substrates effectively suppresses the growth of Cu–Sn and Ag3Sn IMCs. The mechanisms involved are explained in detail using thermodynamic theories and undercooling effects. Owing to the effective suppression of Cu–Sn and Ag–Sn IMCs, Cu/Sn–3.5Ag/Cu–15Zn microbumps are potentially useful in strengthening the interconnections of novel 3D-IC technologies.

Rheological characterization of asphalt binders modified with soybean fatty acids

This investigation examines rheological properties of asphalts blended with soybean acidulated soapstock, a relatively low-cost and highly concentrated source of soybean fatty acids. Rheological tests indicate that as soybean acidulated soapstock is added, binders become softer, less stiff and their high temperature viscosities are reduced. The addition of 1% soybean acidulated soapstock reduces thermal stress accumulation. These findings suggest that soybean acidulated soapstock could be used as a fluxing agent (i.e., consistency reducer) for stiff, hard and viscous asphalt binders, increasing their workability and may improve low temperature performance of an asphalt binder by reducing thermal stress development.

Finite element analysis study on the thermomechanical stability of thermal compression bonding (TCB) joints in tubular sodium sulfur cells

A typical large capacity sodium sulfur (NaS) battery is operated at 300–350 °C with 20–50 °C thermal fluctuations during its charging and discharging. In addition, for maintenance purposes, the cell experiences larger temperature changes down to the intermediate or room temperatures. Such temperature changes can cause mechanical failure of heterogeneous joints such as thermal compression bonding (TCB) joints, which is one of the most critical issues in developing NaS batteries. The present study seeks to build a computational finite element analysis (FEA) model to predict the thermomechanical responses of NaS batteries to the attack induced by the temperature changes. Specifically, the thermomechanical stress accumulation at TCB joints of a tubular cell has been explored during its booting-and-shutdown cycles. Static temperature profiles and simplified friction conditions in the cathode wall were assumed for the model. Using the developed model, the stress components that dominantly contribute the stress accumulation at the joint were identified, and the effects of TCB geometries and container material types on the thermal stress accumulation at the TCB joints were carefully examined. It turns out that the stress accumulation at the bonding interface would be critical for the failure at the TCB joints.

Seasonal Prediction of Thermal Stress Accumulation for Coral Bleaching in the Tropical Oceans

Abstract Mass coral bleaching, associated with anomalously warm ocean temperatures over large regions, poses a serious threat to the future health of the world coral reef systems. Seasonal forecasts from coupled ocean–atmosphere models can be a valuable resource for reef management, providing early warning of potential bleaching conditions, allowing for a proactive management response. Here, the ability of a dynamical seasonal forecast model (Predictive Ocean Atmosphere Model for Australia, POAMA) to forecast degree heating months (DHMs) in the tropical oceans is assessed, with particular focus on the 1997/98 El Niño–Southern Oscillation (ENSO) and associated global bleaching events. The model exhibits useful skill in forecasting sea surface temperatures (SSTs) across the tropical oceans for 1982–2006 and reproduced both the magnitude and distribution of DHM values observed during the 1997/98 ENSO event. In general, observed teleconnections between ENSO indices and tropical SST at various lags are well captured by the model. In particular, strong observed correlations between peak ENSO indices and SST in the Caribbean in the following summer were reproduced. The model also shows skill in predicting ocean conditions conducive to bleaching in non-ENSO years, capturing the anomalously warm conditions in the Caribbean region in 2005. Probabilistic forecasts of DHM values above certain thresholds for the Caribbean show useful skill and could be valuable in the assessment of the likelihood of bleaching for the region.

Multiphysics Characterization of Transient Electrothermomechanical Responses of Through-Silicon Vias Applied With a Periodic Voltage Pulse

Multiphysics characterization of transient electrothermomechanical responses of multilayered stacked through-silicon vias (TSVs) is performed with a modified hybrid time-domain finite-element method. Temperature dependence of most material parameters involved is considered, such as electrical and thermal conductivity, the thermal expansion coefficient, and Young's modulus. Transient temperature and thermal stress accumulation processes are studied in detail for various copper, polycrystalline silicon, and tungsten/polycrystalline silicon TSVs, with different periodic voltage pulses applied. It is shown that there are significant differences in the transient temperature and thermal stress responses among the three types of TSVs, which are all very sensitive to the variation of the surrounding silicon oxide isolation thickness. The algorithm and analysis will be useful in the design of stacked TSVs with high reliability.

The effects of water fluid at temperatures up to 850°C and pressure of 300 MPa on porosity and permeability of amphibolite

Compressional wave velocities were measured in amphibolite under gas and water fluid pressure of 300 MPa and at temperatures up to 850°C. Fluid and confining pressures were equal during the experiments. The data obtained under water pressure differ from those for gas pressure by the reversion of the V p temperature trend: on heating under gas pressure V p decreases throughout the temperature range, whereas on heating under water pressure V p decreases at first, reaches a minimum value at approximately 650°C and then increases. A similar V p trend was determined for quenched samples. For initial and quenched amphibolite samples, porosity, permeability and pore size distribution were measured and the microstructure was examined. It was found that changes in the elastic properties of rock with temperature rise are determined by the transformation of its microstructure. The temperature trends of porosity and permeability are in negative correlation with the V p temperature trends. The increase of effective porosity is caused by initiation of new microcracks and the opening of pre-existing microcracks. The decrease of effective porosity is caused by the sealing of microcracks (mostly thin ones). Two types of processes are responsible for the transformation of pore structure: phase transitions within a narrow temperature range (the high-low quartz transition at T ≈ 650° C, P = 300 MPa, and the partial melting of amphibolite at T = 740–760° C, P = 300 MPa) and processes that take place throughout the temperature range. These latter processes are caused by thermal stress accumulation and relaxation. Under gas pressure, thermally induced microcracking leads to porosity increase and V p decrease. Under water pressure, the processes of microcrack generation and sealing develop simultaneously. At temperatures below 650°C the processes leading to microcrack generation and porosity increase prevail and, as a result, V p decreases. At temperatures over 650°C the processes leading to microcrack sealing and porosity decrease prevail, with a concomitant V p increase.

Evidence for periodic seismicity in the inner Aegean seismic zone

The most complete and reliable data of strong (M s≥6.5), shallow (h<70 km) earthquakes which occurred in the inner Aegean seismic zone have been utilized to describe its seismicity time variation during 1800–1986 by two independent statistical models. The first is a sequentially stationary model of seismicity rates which shows that intervals of low seismicity rate, lasting for some 37 years, alternate with high rate intervals of 8–12 years duration. The second model is a statistical model according which seismic energy released within 5-year time windows approximates a harmonic curve within a period of about 50 years. This model is in agreement with the notion that the time series of strong earthquake occurrences in the inner Aegean seismic zone consists of a random (shocks withM s=6.5–6.8) and a nonrandom component (M s≥6.9). Maxima and minima of the harmonic curve coincide with the high and low rate intervals, respectively. A model of regional stationary accumulation of thermal stresses along certain seismic belts and their cyclic relaxation may explain this periodicity.

The evolution of impact basins: Cooling, subsidence, and thermal stress

Potentially important contributors to the topography and tectonics of multi‐ring impact basins are the thermal contraction and thermal stress that accompany the loss of heat emplaced during basin formation. Heat converted from impact kinetic energy and contributed from the uplift of isotherms during cavity collapse are important components in the energy budget of a newly‐formed basin. That the subsequent cooling may have been an important factor in the tectonic evolution of the Orientale basin is suggested by the deep central depression and by a surrounding region of extensive fissuring. To test these concepts, we develop models for the anomalous temperature distribution immediately following basin formation, and we calculate the resulting elastic displacement and stress fields that then would accompany cooling of the basin region. All models predict subsidence of the basin floor and a near‐surface stress field consistent with fissuring. In addition, the rates of cooling and of accumulation of thermal stress are in agreement with the inferred timing of fissure formation in Orientale. The sensitivity of the predicted displacements and stresses to the initial temperature field allows us to place bounds on the quantity and distribution of impact heat emplaced during basin formation. In order to be consistent with the observed topography and the distribution of fissures in the Orientale basin, the buried heat deposited during the basin‐forming event was between 1032 and 1033 erg. It is likely that most of this heat was concentrated within a distance of 100–200 km from the point of impact.