Temperature Distribution Data Research Articles

The feasibility of external gas-assisted mold-temperature control for thin-wall injection molding

Simulation and experimental testing were conducted on an external gas-assisted mold-temperature control combined with a pulsed cooling system used for thin-wall injection molding to determine its effect on the heating rate and temperature distribution of a mold surface. For mold heating via external gas-assisted mold-temperature control, a hot gas was directly discharged on the cavity surface. Based on the heat convection between the hot gas and the cavity surface, the cavity temperature rose to the target value. Practically, the gap between the heating surface and the gas gate is an important parameter as it strongly influences the heating process. Therefore, this parameter was analyzed under different values of plate-insert thickness herein. Heating was elucidated by the temperature distribution and heating-rate data detected by the infrared camera and sensors. Then, external gas-assisted mold-temperature control was applied for the thin-wall injection-molding part of 0.5 mm thickness with the local-gate-temperature control. The results show that with 300°C gas temperature, the heating rate could reach 9°C/s with a 0.5-mm stamp thickness and a 4-mm gas gap. The results show that with local heating at the melt-entrance area of the mold plate, the cavity was filled with a 20-s heating cycle.

Spatial and temporal temperature distributions in fixed beds undergoing supercritical fluid extraction

Most of the studies dealing with extraction of compounds commonly consider homogeneous beds with constant temperature, although variations might exist. However, understanding that temperature can influence the fluid dynamics and solubility of compounds, this work proposed to evaluate temperature distribution in fixed beds during supercritical CO2 extraction of compounds from turmeric and clove. Two beds of 1 L with different height to diameter ratios were tested. Kinetic curves were determined, extract composition was measured and temperature distribution was mapped. Heating the beds to the desired temperature was readily reached (<5 min) when the beds were pressurized with pre-heated CO2. During pressurization, a significant increase in temperature was observed. Gradients of temperature (until 20 °C) were formed during the extraction mainly in the axial direction. Furthermore, slight variations of ar-turmerone, eugenol, beta-caryophyllene, eugenyl acetate, and alpha-humulene are displayed as a function of spatial and temporal temperature variations in the beds. Experimental data of temperature distribution in fixed beds undergoing supercritical fluid extraction in industrial scale can contribute to improving the productivity (yields) and the quality (composition) of extracts containing bioactive compounds. In food-related areas, bioactive compounds are searched for applications as antioxidant, anti-inflammatory, and antimicrobial agents.

Analytical study of the heat transfer coefficient of the impinging air jet during cold spraying

A semi-empirical analytical model was developed to determine the convective heat transfer coefficient of an impinging air jet generated by a cold spraying nozzle. A low-pressure cold spraying unit was utilized to produce hot air jets that impinged upon a flat substrate surface. An infrared camera was used to measure the surface temperature of the substrate at different time intervals. A method involving Green's functions was employed to solve a transient two-dimensional heat conduction problem to obtain an expression for the temperature distribution within the substrate. By coupling the analytical results of temperature distribution and experimental surface temperature data, the radial variation of the non-dimensional heat transfer coefficient of the impinging air jets upon the substrate was estimated. The results showed that the maximum values of the heat transfer coefficient were present close to the stagnation point of the air jets. It was found that the heat transfer coefficient was independent of the time that the cold spray nozzle remained stationary over the substrate surface. It was found further that by increasing the stand-off distance of the nozzle, the radial variations of the heat transfer coefficient became negligible, compared to those for small stand-off distances. The close agreement between the experimental results and the predictions of the model suggested that the estimated heat transfer coefficient of the cold spray gas jet can be used to estimate the surface temperature of the substrate at any time.

Solid Rocket Motor Propellant Optimization with Coupled Internal Ballistic–Structural Interaction Approach

This research aims to optimize the geometric design of slotted propellant grains for solid rocket motors with respect to coupled internal ballistic performance and structural strength criteria. In-house codes such as a zero-dimensional internal ballistic solver and an analytical burnback solver are implemented to compute the variation of chamber pressure and the rocket thrust transiently. Structural analysis of the solid propellant is achieved by using a parametric linear viscoelastic model and a parametric cooldown heat transfer model, both of which are based on the finite element method. The transient temperature distribution data derived from the cooldown process are required inputs for the material properties to be used in the viscoelastic structural analysis. To enable an efficient optimization process, a surrogate heat transfer model that predicts the cooldown time of the system by eliminating expensive iterations is also implemented and validated. Within a coupled analysis approach, the pressure data obtained from the internal ballistic performance analysis are used for the ignition step of the linear viscoelastic analysis. The structural analysis results are evaluated by using a deterministic approach based on the margin of safety with respect to the stress and strain criteria. Finally, the optimum geometrical parameters for a slotted grain subjected to both structural and internal ballistic performance constraints are investigated through multidisciplinary optimization techniques.

Optical‐Fiber‐Based Smart Concrete Thermal Integrity Profiling: An Example of Concrete Shaft

Concrete is currently the most widely used construction material in the world. The integrity of concrete during the pouring process could greatly affect its engineering performance. Taking advantage of heat production during the concrete curing process, we propose an optical‐fiber‐based thermal integrity profiling (TIP) method which can provide a comprehensive and accurate evaluation of the integrity of concrete immediately after its pouring. In this paper, we use concrete shaft as an example to conduct TIP by using the optical fiber as a temperature sensor which can obtain high spatial resolution temperature data. Our method is compared with current thermal infrared probe or embedded thermal sensor‐based TIP for the concrete shaft. This innovation makes it possible to detect defects inside of the concrete shaft with thorough details, including size and location. First, we establish a 3D shaft model to simulate temperature distribution of concrete shaft. Then, we extract temperature distribution data at the location where the optical fiber would be installed. Based on the temperature distribution data, we reconstruct a 3D model of the concrete shaft. Evaluation of the concrete integrity and the existence of the potential defect are shown in the paper. Overall, the optical‐fiber‐based TIP method shows a better determination of defect location and size.

基于Fluent的飞行器流场建模与红外辐射特性分析

Taking a fighter aircraft as the research object, the flow field calculation model of the aircraft was established by the three-dimensional modeling and meshing process, and the numerical simulation of the flow field characteristics of the aircraft was carried out based on the commercial CFD software ANSYS Fluent 16. The effect of solar radiation on the temperature field of the fuselage was considered by using the solar ray tracing algorithm, the discrete ordinates method for DO radiation model was used to calculate the iterative calculation of the radiation transfer equation, simulating the after-combusting tail flame injection process with component transport model without chemical reaction (Species Transport Model), and the temperature, concentration and component distribution data of the outflow field of the aircraft were obtained. The influence of solar radiation on the whole temperature field distribution, the influence of the Mach number on the infrared radiation of the flow field and the distribution of tail flame flow field were simulated and analyzed. Analysis shows that the effect of solar radiation on heating of the skin is only about 5 K. With the increase of the number of Mach aircraft fuselage and the difference of infrared radiation intensity is highest in the abdomen, abdominal radiation intensity is about 2 times the maximum radiation intensity. Under the shock wave, there will be the core high temperature region with the highest two 450 K and 580 K discontinuity at the rear of the tail flame. The infrared radiation intensity distribution of the plume conforms to the pear shape distribution trend.

Thermal Simulation Analysis for Cabinet of Carborne Controller Based on Finite Element Analysis

The simulation analysis for cabinet of carborne controller is carried out by Fluent software in this paper. The different analysis result of temperature distribution, wind speed and other data is obtained .The better design of wiring chassis is chosen by comparison.

Reconstruction method for inversion problems in an acoustic tomography based temperature distribution measurement

In industrial areas, temperature distribution information provides a powerful data support for improving system efficiency, reducing pollutant emission, ensuring safety operation, etc. As a noninvasive measurement technology, acoustic tomography (AT) has been widely used to measure temperature distribution where the efficiency of the reconstruction algorithm is crucial for the reliability of the measurement results. Different from traditional reconstruction techniques, in this paper a two-phase reconstruction method is proposed to ameliorate the reconstruction accuracy (RA). In the first phase, the measurement domain is discretized by a coarse square grid to reduce the number of unknown variables to mitigate the ill-posed nature of the AT inverse problem. By taking into consideration the inaccuracy of the measured time-of-flight data, a new cost function is constructed to improve the robustness of the estimation, and a grey wolf optimizer is used to solve the proposed cost function to obtain the temperature distribution on the coarse grid. In the second phase, the Adaboost.RT based BP neural network algorithm is developed for predicting the temperature distribution on the refined grid in accordance with the temperature distribution data estimated in the first phase. Numerical simulations and experiment measurement results validate the superiority of the proposed reconstruction algorithm in improving the robustness and RA.

Preliminary forensic engineering study on aggravation of radioactive releases during the Fukushima Daiichi accident

Even after 6years since the Fukushima accident, the exact accident progression for each unit and location of core debris have not been clarified, although solidified low-melting metal debris was identified at the bottom of the 1F3 reactor pressure vessel (RPV) in July 2017. Currently efforts are directed towards robotic inspection with remote cameras, as well as dose and temperature measurements of the environment inside the Primary Containment Vessels (PCV). In spite of their effort, the observed environmental temperature distribution data does not support the existence of a significant radiation heat sources attributable to the molten core at the bottom of the PCV. At this point the total decay heat of the core debris should be as large asa few hundred kilowatts after 2000days since the initiation of the accident as summarized in Annex A. In addition, the temperature of the accumulated water inside PCVs is 10–20°C even with a reduction of the water injection to 3.0m3/h. The RPVs appear to be holding the heating core debris with water, implying that “in-vessel retention” of core debris has been achieved thanks to effective accident management. This should help greatly in the retrieval of the core debris by removing the top head of RPV.Under these circumstances the author has conducted a forensic engineering study (i.e., different fields of science working together to collect and integrate independent evidences) to clarify the most likely accident scenarios of the Fukushima Daiichi accident. Through this study the author identified that a large portion of the land contamination observed at the north-west direction is mostly the result of the accident that occurred at Unit 2.In this unit its blowout panel, provided for over-pressure protection against a main steam pipe breach in the secondary confinement building, was inadvertently activated before a leakage of radioactive effluent from the PCV. Its activation is believed due to the hydrogen explosion in Unit 1 which occurred on March 12, next day of the Fukushima accident initiation. By losing the confinement function, the radioactive effluent leaked from the 1F2’s PCV and would have been discharged without mitigation. This accident scenario explains the series of leakage events identified in two of the 24 monitoring posts which had been installed by the Fukushima Prefectural Government. A series of six large releases were repeated between March 15 and 16, behaving like a periodical actuation of the safety valves for the PCV. Such multiple release events were very likely induced by the overpressure release of the PCV due to leakage of the dry well flange. This leakage should have been induced through discharging steam and hydrogen due to the activation of Safety and Release Valves (SRV) into the suppression pool (SP) water. Unfortunately the wet well atmosphere must have been that of air, since there was no nitrogen charge line to the atmosphere of the SP surface water. The resultant air-hydrogen mixture resulted in an “internal hydrogen explosion” which should have deformed the flange. The recent robotic inspection inside PCV revealed that a gigantic water splash appears to have occurred at the bottom of the PVC dislodging the gratings installed over the platform.Next to the series of large releases from Unit 2, Unit 1 also induced two large releases on March 12. Fortunately, these releases left more than 3 orders of magnitude less soil contamination compared with the series of releases from Unit 2. Unit 3 also released a significant amount of radioactive species twice on March 13, resulting in a very small soil contamination. The main constituent of the radioactivity is likely radioactive noble gases in this unit.

Experimental investigation of convective heat transfer in an inserted coiled tube type three fluid heat exchanger

In the present study, an experimental investigation of a three fluid heat exchanger (TFHE) has been performed. The TFHE presented here is an improved version of double pipe heat exchanger, where a helical tube is inserted between two concentric straight tubes. The curvature ratio, δ = 0.1315, pitch to inside diameter, p/dci = 2.88 of the helical tube are taken constant during the test while range of coil side Reynolds number are varied between 9000 and 54,000 during this investigation. Coil side Nusselt numbers are calculated using traditional Wilson plot technique and compared with the Nusselt numbers reported from literature for both parallel and counterflow configurations. Temperature distribution data has been obtained using analytical approach and experimental approach for three fluids. The effect of variation in volume flow rate on performance of the TFHE is assessed as well. Overall heat transfer co-efficient found to be increased in each case when flow rate of different fluids in TFHE increased. The effectiveness decreases or increases, which are the combined effect of residence time, capacity ratio, R and NTU. TFHE provides optimized performance, when flow rate of normal water increases in counter flow configuration. Simultaneous space heating and water heating is the novelty of the proposed TFHE.

An IR thermal imaging method to investigate spreading process of ethanol solution droplets on carbon fiber mats

Porous media are a class of basic engineering material, and the applications of a porous medium are significantly influenced by its surface and bulk wettabilities. Conventionally, the surface wettability and dynamics of a liquid droplet on a stationary material surface can be observed by performing a dyed droplet spreading test captured with a high-speed camera. Such a method, however, is not effective in the quantification of droplet dynamics within a porous medium. In this work, we propose an infrared (IR) thermal imaging method to investigate the spreading of colorless droplet beneath the surface of, and within, the porous network of the porous medium. The spreading rim of a colorless droplet is accurately detected by the locations of extreme points in its temperature gradient curve, as deduced from temperature distribution data collected by an IR camera imaging from the top. Compared with the images captured simultaneously by a high-speed camera from the side, the droplet spreading rim is revealed to be an inner precursor rim located inside the porous media. To evaluate this method, carbon fiber (CF) mats with different porosities are used as the porous media. The spreading velocities of droplets in CF mats are measured successfully and coincide exactly with conclusions obtained by the background subtraction method. This finding validates the effectiveness of IR thermal imaging method in a droplet spreading test. This work demonstrates that IR imaging holds great promise in the visualization of the inner precursor rim of droplets in porous media.

Electrochemical-Thermal Characterization and Modeling of Large Format Prismatic Lithium Ion Batteries

Large-format prismatic lithium-ion cells can generate substantial heat during operation, making thermal management significant. Some cells have high surface-to-volume ratios, and the positioning of tabs can make surface temperature highly non-uniform [1], posing further thermal management challenges. Non-uniformity of temperature is a major problem because a battery operated at a safe average temperature can still have ‘hot spots’ that are prone to thermal runaway [2]. Depending on the battery’s ability to dissipate heat to its surroundings, thermal runaway may nucleate in very small volumes. The thermal responses of prismatic lithium-ion batteries arise from a number of distinct phenomena that occur as the cell is subjected to an electrical load. Current flow generates joule heat, which is always dissipated, regardless of the sign of the current; this may arise either from ohmic resistance or from the resistances associated with charge-transfer reactions. There is also reversible heat, which may be dissipated or consumed according to the current’s sign; such heat owes to the entropy associated with the electrochemical reaction that occurs as the state of charge (SOC) is changed [3]. We have developed a 3D finite-element model that accounts for these various modes of heating within the battery cell, which runs with sufficient computational efficiency to allow parameterization by fitting model output to dynamic experimental voltage and temperature-distribution data. Our approach provides an ‘outside-in’ method that allows external measurements to be correlated with internal material properties. A simple physics-based model based on the Newman-Tobias porous-electrode theory [4] is augmented with energy equations to predict electrical and thermal behavior. The model can then also be used to extract material properties. We aim to characterize the macroscopic effects of charge/discharge induced thermal response across a cell’s available charge states to provide insight into battery state of health (SOH). Square wave signals with amplitudes of C-rates ranging from 1C to 4C and periods ranging from 20s to 100s were applied to A123 20Ah LiFePO4 prismatic cells beginning at fixed SOC. This input signal was chosen so that the average SOC remains constant, eliminating concerns regarding how material properties change depending on charge state. Temperature distributions were measured using infrared thermography; this data was gathered dynamically and synchronized with the cell-voltage data gathered during the square-wave excitation tests. Figure 1 shows typical temperature distributions across three C-rates (1C, 2C, 4C) at a fixed period of 100s at an average SOC of 50%. As C-rate increases, not only does the overall temperature of the cell increase, but the difference in temperature across its surface also varies. Material properties of batteries – including the propensity for thermal runaway – depend strongly on SOC [5]. By fitting the thermographic data gathered around different mean SOCs, it is possible to extract these SOC-dependent parameter values. Some discussion will also touch on how the model can be used to track material properties as they vary with respect to cycling history, providing possible insight into SOH estimation. 1. Robinson, J.B., et al., Detection of Internal Defects in Lithium-Ion Batteries Using Lock-in Thermography. ECS Electrochemistry Letters, 2015. 4(9): p. A106-A109. 2. Bandhauer, T.M., S. Garimella, and T.F. Fuller, A Critical Review of Thermal Issues in Lithium-Ion Batteries. Journal of The Electrochemical Society, 2011. 158(3): p. R1-R25. 3. Thomas, K.E. and J. Newman, Heats of mixing and of entropy in porous insertion electrodes. Journal of Power Sources, 2003. 119–121: p. 844-849. 4. Newman, J.S. and C.W. Tobias, Theoretical Analysis of Current Distribution in Porous Electrodes. Journal of The Electrochemical Society, 1962. 109(12): p. 1183-1191. 5. Maleki, H., et al., Thermal Stability Studies of Li‐Ion Cells and Components. Journal of The Electrochemical Society, 1999. 146(9): p. 3224-3229. Figure 1

Investigating ventilation system performance in large space building: A nozzle primary air supply with secondary airflow-relay system

In large space buildings, nozzle is usually used for ventilation and air conditioning. A secondary airflow-relay system is proposed for situations that building span is larger than the primary jet flow range. A field measurement was conducted to investigate the performance of primary airflow nozzle and secondary jet fan system; a computational fluid dynamics model was built up to research the secondary airflow velocity and relative location of primary and secondary terminal on the ventilation performance. The performance of different computational fluid dynamics turbulence models in predicting the primary jet trajectory path was evaluated by comparing predicted result with field measurements. The temperature field predicted by computational fluid dynamics method was also validated by experimentally measured vertical temperature distribution data in certain measurement points. Various indices including Air Diffusion Performance Index, percentage dissatisfied, and coefficient of variation of temperature and velocity at breathing level were used to quantitatively evaluate the ventilation performance of different configurations. It is found that re-normalization group k-ϵ turbulence model gives the best overall prediction on the primary air nozzle jet trajectory path and field temperature distribution. In a certain large space building utilizing secondary airflow system, the relative location of primary and secondary equipment and air velocity should be properly specified in order to improve the ventilation performance of a large space building. The secondary airflow-relay may potentially increase the cooling energy consumption as indicated by computational fluid dynamics result.

Simulation Research on the Thermal Effects in Dipolar Illuminated Lithography

The prediction of thermal effects in lithography projection objective plays a significant role in the real-time dynamic compensation of thermal aberrations. For the illuminated lithography projection objective, this paper applies finite element analysis to get the temperature distribution, surface deformation and stress data. To improve the efficiency, a temperature distribution function model is proposed to use for the simulation of thermal aberrations with the help of optical analysis software CODE V. SigFit is approved integrated optomechanical analysis software with the feature of calculating OPD effects due to temperature change, and it is utilized to prove the validation of the temperature distribution function. Results show that the impact of surface deformation and stress is negligible compared with the refractive index change; astigmatisms and 4-foil aberrations dominate in the thermal aberration, about 1.7 λ and 0.45 λ. The system takes about one hour to reach thermal equilibrium and the contrast of the imaging of dense lines get worse as time goes on.

Fire spill plume from a compartment with dual symmetric openings under cross wind

This paper presents a comprehensive theoretical and experimental study on the fire spill plume from a compartment with dual symmetric openings under cross wind. Experiments of spill plume were performed at the outlet of a wind tunnel using a bench-scale compartment with a leeward façade wall and dual symmetric openings. The experimental fire compartment was well-mixed. The effect of wind is theoretically elucidated by derivations on the pressure differences between inside and outside. The neutral planes for the two openings are theoretically formulated and compared with those in single-opening and no-wind case. The formulations of the neutral plane heights are verified by using video image analysis and velocity data regression analysis. Also a new method using the data of wind speed and neutral plane height in no-wind case is proposed to determine the neutral plane heights for higher wind speeds. The results suggest that the neutral plane heights vary monotonically with cross wind speed. Two new length scales with variable neutral plane heights are proposed by theoretical derivations to develop scaling models of spill plume. It is indicated that the new length scales are applicable to correlate the axial plume temperature and the total heat flux along the façade. The radial temperature profiles of spill plumes are well described by a Gaussian function normalized by the temperature radius, which is independent on the wind speed. It is found that wind enhances the air entrainment of spill plume in both the near and far fields, thereby the transition from continuous flame, intermittent flame to buoyant plume is accelerated. The data of total heat flux and temperature distribution along the façade indicate that cross-wind has two competitive effects on the heat transportation from the spill plume to the façade.

Performance measurement of a new type chassis

This work reports the measurement results of a mock-up chassis that has the same structure as the center column of a real 4U chassis to be developed. The reported results include the measurement data of temperature distribution, vibration level of chassis frame and disk drive holder, and throughput of each disk drive of the mock-up chassis as well as the reliability test of the chassis. Some critical factors that affect the throughput performance will be addressed and discussed. The suggestions to improve the chassis design will be mentioned based on the observations during the mock-up chassis testing and measurement.

Effect of thermal boundary conditions and thermal conductivity on conjugate heat transfer performance in pin fin arrays

The present work experimentally investigates the conjugate heat transfer performance for pin fin arrays. The geometry of pin fin arrays is typical of x/D=y/D=2.5 and H/D=1. The effect of two main factors: material thermal conductivity and thermal boundary conditions, i.e. conjugate and convective boundary conditions, are quantified by comparing the nondimensional temperature and Nusselt number.For conjugate heat transfer, models are constructed with materials with thermal conductivity ranging from 0.23Wm−1K−1 to 16Wm−1K−1. Uniform heat flux is imposed along the external wall of pin fin arrays and highly resolved temperature distributions of internal wall is obtained with steady liquid crystal, meanwhile external wall temperature is measured through thermocouples. For convective heat transfer, model is constructed with low thermal conductivity material to ensure the usage of transient liquid crystal to obtain heat transfer coefficients of the internal wall on the same configuration.Experimental data of temperature and heat transfer coefficient distribution is used as boundary conditions to conduct FEM calculations of pin fin array. Internal and external wall non-dimensional temperature distributions, as well as iso-thermal line distributions of the whole domain, are compared. Results indicate that thermal conductivity can significantly impact the heat transfer capacity, i.e. Nusselt number; meanwhile, the necessity of taking conjugate heat transfer effect is demonstrated by comparison with purely convective results.

Cracking Response of a Concrete Wall to Cryogenic Temperature

Liquefied natural gas (LNG) has the cryogenic temperature of –160°C to ensure the minimum storage volume when stored in LNG containers. Among various types of LNG storage containers, the full containment above-ground type with a double safety system (outer concrete tank and inner steel tank) is very common. Normally, the inner tank contains LNG, but when the LNG leaks from the inner tank, the outer concrete tank comes into contact with LNG. Under this accidental case, it is indispensable for the outer wall to keep the liquid tightness in order to safely contain the LNG before taking any countermeasure. It is, therefore, proposed to take up a heat conduction problem using the finite element method with the ANSYS software to obtain temperature distribution data of a concrete wall at cryogenic temperatures.

Transient Joule heating of graphene, nanowires and filaments: Analytical model for current-induced temperature evolution including substrate and end effects

Transient Joule heating of graphene or nanowires, supported by substrates, is an important and complex heat transfer problem to be solved in the context of nanoscale electronic devices. We formulate here an analytical model that allows the examination of the effects of input power, heat transfer through substrate and the end contacts on the transient temperature evolution. An exact analytical solution is obtained here by the superposition of the Joule heating, the substrate heat transfer and the temperatures at the ends of contacts, within the Fourier formalism, through Laplace transformations. The transient solution explicitly relates temperature profile to the input power, size and the thermal properties of the element, and the heat transfer properties of the substrate. The transient solution naturally reduces to steady state solution. The solutions can be useful for the thermal design of devices made of graphene or nanowires or electrically heated filaments. Experimental steady-state temperature distribution data, obtained by 2D phonon band spectroscopy, are used to confirm the accuracy of the solution. It is found that the time to achieve steady-state temperatures in graphene is of the order of nanoseconds and is a strong function of substrate heat transfer. Further, the maximum temperature and the gradient in steady state profile temperature profile are greatly affected by heat transfer to the substrate.

Numerical Modeling and Initial Fatigue Life Estimations of Welded Structural Components

Numerical simulations are powerful tool for analyzing and research in domain of mechanical constructions. In welded joints is very important to determine residual stresses and temperature distribution in sample, apropos, element of construction. In some cases doing the experiment is not possible, so numerical simulations can give the required results and overview of stress state, residual stresses, critical areas, displacement, temperature distribution and other data is needed for analyzing and improvement of constructions or parts of constructions. This analysis includes finite element model for the thermal and mechanical welding simulation. Welding simulation was considered as a sequential coupled thermo-mechanical analysis. The residual stress distribution and magnitude in axial direction was obtained. The paper also shows the results obtained in a simultaneously test of a butt welded thin steel sheet specimen by conventional methods and thermography. Numerical methods are also used in order to predict the crack of specimen. The obtained results confirm that it is very useful to use thermography and Finite Element Method (FEM) for early diagnostics of the complex structures in the exploitation conditions. In this paper is obtained good agreement of results between experiment and Numerical simulations.