Cyclic Thermal Stress Research Articles

Cycled Thermomechanical Failure in 808-nm High-Power AlGaAs/GaAs Laser Diode Bars

Thermomechanical cycle failure was analyzed in 808-nm high-power AlGaAs/GaAs laser diode bars (LDBs) in detail. Two thermal stress cycle experiments were carried out in these devices with peak thermal stresses of 19.4 and 33 MPa. The threshold current increase demonstrated a square-root dependence on the cycle number, and a tail and split in lasing spectrum were observed. This result was attributed to nonradiative recombination increasing with cycle number due to the diffusion of defects that accompanies band-structure renormalization. Furthermore, from X-ray diffraction measurements we found that the epitaxial layer remains monocrystalline during thermal stress cycling. We calculated the out-of-plane strain and in-plane stress induced by plastic deformation in the epitaxial layer based on the interplanar spacing in the crystal. Our results suggest that thermomechanical strain and stress were induced by pulsed operation, which led to degradation of the high-power LDBs.

Solid-state bonding of superplastic ultra-high carbon steel and structure steel with an interlayer

Solid-state bonding between two superplastic steels-ultra-high carbon steel (UHCS) and a structure steel (commonly referred to as 40Cr in china; yet contains only 1 mass% Cr)- was investigated. Industry-grade pure iron sheet was used as an interlayer and the bonding was carried out at the superplastic deformation temperature T = 750 °C . For a pre-pressing stress of P = 56.6 MPa, the initial strain rate was 1.5 × 10−4s−1, and for a bonding time of t = 10min, the joint tensile strength reached up to 702 MPa a value 35% higher than what could be obtained without an interlayer. The bonding strength reached the tensile strength of 40Cr base metal through the same thermal-stress cycling. Based on the results, it was concluded that the weldability of 1.6 mass%C-UHCS / 40Cr steel was improved by using a pure iron interlayer.

Low Cycle Fatigue Analysis of after Treatment Device Induced due to Thermal Load by Using Finite Element Analysis

Cyclic thermal loading causes cyclic thermal stress and thermal fatigue in the component. The goal of this paper is to characterize the thermal fatigue behavior of after-treatment (AT) device, i.e. Exhaust Gas Processor (EGP) and prediction of crack initiation cycles. The paper contains transient thermal analysis to map temperature on EGP model. By taking temperature distribution as input, Elasto-plastic structural analysis is done. Based on stress-strain data and fatigue material property, crack initiation cycles are estimated. For low cycle fatigue analysis, strain based approach, i.e. Brown-Miller Criteria with Morrow mean stress correction factor [1] is used. The von-Mises stress and crack initiation cycles are investigated and S-N curve and Ɛ-N curve are compared with standard graphs.

Thermal fatigue crack growth behaviours of laser deposited Ti60A near α titanium alloy

Thermal fatigue damage of high temperature titanium alloys and thermal fatigue crack growth (TFCG) behaviours are of great concern for severe temperature fluctuating environments. Cyclic thermal fatigue tests of heating to 700°C for 55 s followed by water cooling for 3 s at 20°C per cycle were performed with laser deposited Ti60A (Ti–5·54Al–3·38Sn–3·34Zr–0·37Mo–0·46Si) alloy. Thermal fatigue crack growth paths including crack length and crack growth directions were examined, as were their correlations with microstructure changes during the thermal fatigue process. Results show that local coarsened lamellar α developed by the interaction between cyclic thermal stress and oxygen atom interstitial solution effect occurs in the alloy after 800 cycles. Thermal fatigue cracks initiate after 800 cycles. Subsequently, total crack length increases with the volume fraction of local coarsened lamellar α from 800 to 2000 cycles. The enhanced oxygen penetration process plays a key role in the TFCG process.

Estimation of the degradation rate of multi-crystalline silicon photovoltaic module under thermal cycling stress

The overall power of an outdoor-exposed photovoltaic (PV) module decreases as a result of thermal cycling (TC) stress, due to the formation of cracks between the solder and metal. In this study, the thermal fatigue life of solder (62Sn36Pb2Ag) interconnection between copper and silver metallization in PV module was studied. This paper describes in detail the degradation rate (RD) prediction model of solder interconnection for crystalline PV module. The RD prediction model is developed which based on published constitutive equations for solder and TC test results on actual PV module. The finite element method was employed to study the creep strain energy density of solder interconnections in TC conditions. Three types of accelerated tests were conducted to determine the prediction model parameters. RD in benchmark condition is predicted and compared with those of TC conditions.

Indirect determination of martensitic transformation temperature of sintered nickel-free Ti–22Nb–6Zr alloy by low temperature compression test

Nickel-free Ti–22Nb–6Zr alloys were fabricated by conventional powder metallurgy sintering method. X-ray diffractometer (XRD) investigation showed that the as-sintered alloys mainly consisted of β phase, with a few needle-like α phase precipitates. Differential scanning calorimetry (DSC) measurement in the temperature ranging from −70°C to 400°C and constant stress thermal cycling test by dynamic mechanical analysis (DMA) were unable to reveal the martensitic start temperature of sintered Ti–22Nb–6Zr alloys. Therefore low temperature compression tests were carried out to evaluate their phase transformation behavior indirectly. There was an obvious drop of both Young’s modulus and recoverable strain at −85°C∼−80°C in the Young’s modulus-temperature and recoverable strain–temperature curves of sintered Ti–22Nb–6Zr alloys respectively, which was attributed to the occurrence of thermal elastic martensitic transformation at this temperature. At the testing temperature of −85°C, a superelasticity of as high as 5.9% was achieved in the sintered alloys. The results had revealed that sintered Ti–22Nb–6Zr alloys own a great superelasticity intrinsically and would exhibit a much greater superelasticity at room temperature if their martensitic transformation start temperature (Ms) were closer to room temperature. Along with their noble biocompatibility, sintered nickel free Ti–22Nb–6Zr alloys are thus thought to be potentially competitive biomaterials for biomedical applications.

Cement design for underground gas storage well completion

In order to shave the peak demands during the cold seasons, underground gas storage (UGS), balancing the supply-demand chain throughout the year, has been accepted as a strategic method. During the successive UGS cycles, the well cement experiences cyclic mechanical, thermal, and hydraulic stress and may crack due to its low elasticity and ductility. This could lead to the transmission of stored gas through cementing behind casing, one of the major challenges experienced in UGS operations, so posing high workover costs on UGS wells. In addition to workover costs, the loss of inventory due to gas transmission makes the reservoir insufficient in proper gas supply during the high-demand season. In this work, a new formulation has been invented in order to prevent cement cracking, improve cement elasticity and ductility, and reduce the crack propagation in the cement used for completion of UGS well. The new formulation adds a polymer and an elastomer to cement composition. Results showed that addition of latex to cement decreases the density, hydration and fluid loss of cement; also, the rate of cement bonding decreases. On the other hand, addition of polypropylene fibers results in dramatic improvement of compressive strength and stress strain properties of the cement. In comparison with elastomer, this additive provides a higher threshold elasticity of cement. Also, the combined cohesive effect of latex and flexibility of microfibers brings about the best resistance against excessive pressures.

Reliability study of thermal cycling stress on smart power devices

In this paper, we describe a smart power device degradation behavior under thermal cycling stress. An innovative test structure was developed, which faithfully reflects a stress state caused by the smart power device during operation. From our experiment, the device degraded after millions of fast thermal cycling pulses. We discovered that via destruction was the cause of the device degradation. For the duration of thermal cycling stress, the via resistance increased gradually, and finally increased rapidly at the point of millions of cycles. A failure via was observed, which was broken into two parts. Therefore, the via disconnection was considered to be due to thermo-mechanical stress or electro-migration. Some experiments were conducted, and we demonstrated that the via destruction dominated to the thermo-mechanical stress introduced by the thermal cycling stress.

Accelerated Aging of a Solar Absorber Material Subjected to Highly Concentrated Solar Flux

To support the fast growth of Concentrating Solar Power (CSP) technologies, R&D efforts need to be continued to minimize costs. Reducing manufacturing, processing and maintenance costs is key to reach a competitive low production price for electricity.From this perspective, one issue that becomes increasingly significant is the service lifetime of solar absorber materials. In solar tower receivers, absorber materials are subjected to very intense solar flux and cyclic thermal stresses. The chemical and physical aging mechanisms such as corrosion and oxidation, or the possible apparition of cracks or delamination are responsible for the change of the material's surface and bulk properties over time. This causes the thermal performance of the material to decline more or less rapidly.Taking a two-layer solar absorber material (metal + coating) that is commonly used in power tower receivers (SOLAR TWO, GEMASOLAR, SOLHYCO), we have designed several accelerated aging tests by analyzing the thermal behavior of the material in permanent and variable regimes. The experimental tests consist in subjecting the material to cyclic irradiance of variable intensity, amplitude and period to determine the fastest and most realistic tests. A Solar Accelerated Aging Facility (SAAF) was built for this purpose. It is made of a 2-meter diameter parabola concentrating the solar radiation (up to 16,000 times) onto a material sample that is cooled by air or water in direct contact with its rear face. A flux sensor coupled to a shutter allows us to apply the desired solar irradiance while an infrared pyrometer monitors surface temperature of the sample.Following different constant-irradiance solar aging treatments, the properties that are characteristic of the aging are estimated. The normal solar absorptance of each sample is evaluated by a solar optical fiber reflectometer. The thermophysical properties of the paint such as the thermal diffusivity, effusivity, conductivity and the thermal contact resistance between the paint layer and the metal substrate are estimated by inverse method using the measurements of an impulse photothermal experiment. In addition, untreated samples are characterized in order to provide rare data on the ‘not aged’ material.Careful attention should be paid to the preliminary vitrification heat treatment carried out to give the black paint its optimal absorption properties before being used. The results of the aging tests show a slight deterioration of the properties corresponding to the first aging signs of the material. The solar absorptance and the thermal effusivity of the paint coating are the most affected properties during the tests.

Analysis preheat effect on thermal cycle and residual stress in a welded connection by FE simulation

Preheat effect on thermal cycle and residual stress was studied by employing a 3D finite-element method. A circumferential multi-pass butt weld of pipes based on ASME section IX was investigated and the experiment for thermal cycle validation was carried out. A spherical heat source density with a Gaussian distribution was employed and by an appropriate coordinate system, the rotation of electrode around the pipe was modeled reasonably. Sequentially coupled, thermal–mechanical analysis was applied using temperature-dependent thermo-mechanical behavior for material properties and the variation in peak temperature, cooling rate, and the axial residual stress due to the preheat effect were evaluated.The simulation results revealed that the pattern of final residual stress was influenced by the preheat temperature. However the thermal cycle experienced in the welding zone seems to be significantly affected by the preheat temperature.

THERMAL FATIGUE ANALYSIS OF INDUCTION MELTING FURNACE WALL FOR ALUMINA RAMMING MASS

Furnaces are most commonly used for melting of materials. Induction furnaces are more beneficial as no fuel is required. It is a problem to find life of Induction Melting Furnace wall under thermal fatigue. The induction melting furnace wall is made of silica ramming mass which is one kind of refractory material. The failure occurs due to cyclic thermal stresses. Temperature distribution and thermal stress distribution fields of the induction melting furnace refractory wall were calculated by using ANSYS finite element analysis software based on the physical description of its failure under thermal fatigue conditions. The thermal fatigue life of the refractory wall is required to be found out by means of thermal stresses created inside the refractory wall of induction melting furnace from modified S - log N Curve.

Effect of strain rate on low cycle fatigue with hold time in 9Cr rotor steel

One of the main mechanisms of turbine rotor damage is cyclic thermal stress produced during transition conditions, such as warm-up and shutdown processes. In this paper, the cyclic damage with ramp rate is studied in terms of material properties. To evaluate thermal stress damage during the cyclic operation, experiments were carried out on low cycle fatigue with hold time and a range of strain rates for COST FB2, 9Cr ferritic steel. Initially, the experimental fatigue life was evaluated using the time fraction and ductility exhaustion methods. The two analysis methods are compared with real life cases of different hold times and strain rates, and the accuracy is discussed. Next, to predict the plastic deformation curve for low cycle fatigue with hold time more accurately, an attempt was made to simulate cyclic hysteresis loop behaviour numerically using a time dependent viscoplastic constitutive model, and this was compared with the experimental hysteresis loop curve for each cycle number.

Eutectic Zn-Al Die Attachment for Higher Tj SiC Power Applications: Fabrication Method and Die Shear Strength Reliability

This paper comprehensively describes the fabrication method and shear strength reliability of a eutectic Zn-Al (m.p. = 382°C) attachment system, built by soldering SiC dice (2 × 2 mm2) onto Cu foil active-metal-brazed with a SiN ceramic plate. Four essential soldering conditions are presented and discussed for the formation of a strong and reproducible attachment. Die shear strength reliability data at Tj = 250°C are reported here for the first time. Storage tests at 250°C revealed that, after an initial slight decline, the die shear strength stayed virtually constant at a sufficient level (∼110 MPa) for at least 3,000 h. Thermal cycle test results indicated that the attachments can withstand thermal cycle stress for 3,000 cycles between −40°C and 250°C. The average die shear strength after 3,000 cycles was 18.5 MPa, a value that is three times higher than the IEC standard of 6.2 MPa specified in Document 60749-19.

A novel approach to wear testing in hot stamping of high strength boron steel sheets

Hot stamping of high strength steel sheets was developed in the automotive industry for the production of components characterized by a high strength-to-weight ratio and an increased resistance to impact. In order to avoid scaling and decarburization, the steel blanks are usually coated with an Al–Si coating that has proved a relevant influence also on their tribological behaviour during the forming stages. However, the knowledge of the influence that this coating may have on the dies wear mechanisms is still inadequate.The paper proposes a novel approach to wear testing, based on a pin-on-disk testing configuration, capable to reproduce in a laboratory environment the conditions arising at the interface between the dies and the blank, by reproducing the sliding velocities at the interface and the cyclic thermal and mechanical stresses on the die material. Investigations were carried out on a hot working tool steel sliding against high strength steel blanks coated with the Al–Si coating under dry reciprocating sliding conditions. Scanning electron microscopy and 3D profilometer analysis were utilized to evaluate the wear mechanisms.The presented results show that the proposed procedure can properly simulate the thermal and mechanical cycles to which the forming dies are subjected during the hot stamping process, allowing to control and vary a number of parameters characterizing the industrial process. The presence of both adhesive and abrasive wear mechanisms is highlighted and a possible explanation of their appearance is given.

FAILURE MODE CHARACTERIZATION IN INKJET-PRINTED CPW LINES UTILIZING A HIGH-FREQUENCY NETWORK ANALYZER AND POST-PROCESSED TDR ANALYSIS

Failure mode characterization was applied to coplanar transmission lines by utilizing 0.5{10-GHz S-parameter measurements and post-calculated TDR (Time-Domain-Re∞ectometry) analysis. Coplanar waveguide transmission lines were inkjet-printed on 1.0-mm- thick ∞exible plastic RF substrates. Inductive, resistive, and capacitive types of failures | as the main failure modes caused by manufacturing, bending, or thermal cycling stresses | were investigated. The inkjet- printed CPW (Co-Planar Waveguide) lines were damaged by inductive shorts due to mechanical hitsor resistive and capacitive failures due to bending of the substrate. By using the TDR method the type and physical location of the failure can be determined.

OS1423 き裂成長予測による低サイクル疲労の損傷評価 : 繰返し熱応力下での疲労寿命

The influence of crack growth on the fatigue life was investigated for a ramp change in the fluid temperature on the surface. The stress intensity factor was obtained by the weight function method considering the stress gradient in the thickness direction. The estimated fatigue life under the cyclic thermal loading could be 1.6 times longer than that under the uniform stress distribution. The critical size for the fatigue life determination was assumed to be 3 mm for fatigue test specimens of 10 mm diameter. By determining the critical size by structural integrity analyses, the fatigue life was increased under the cyclic thermal stress.

Damage Assessment of Low-Cycle Fatigue by Crack Growth Prediction (Fatigue Life under Cyclic Thermal Stress)

Damage Assessment of Low-Cycle Fatigue by Crack Growth Prediction (Fatigue Life under Cyclic Thermal Stress)

LORD SolderBrace™ Wafer Applied Coating for Improved Reliability and Throughput in WLCSP

As more manufacturers look to increase the size of Wafer Level Chip Scale Package (WLCSP) dies and also look to decrease the ball pitch, the susceptibility of the die to fail during thermal cycling and drop shock testing increases. The stress conditions introduced during thermal cycling from the mismatches in Coefficients of Thermal Expansion (CTE) lead to solder fatigue. The failure of WLCSPs during drop shock is found at the solder/pad interface. The general solution to address solder fatigue during thermal cycling and solder joint stress at the copper pad interface has been capillary underfilling the chips after chip attachment. To address these issues, a new material from LORD Corporation – SolderBrace™ wafer applied coating, can be used to partially underfill the WLCSP die at the wafer level. This type of technology can be applied using existing equipment and processing techniques making these materials a more cost effective solution. This new material technology has enabled thermal cycling reliability improvements by replacing the final passivation layer with a new low CTE material as the partial underfill. This wafer applied partial underfill material technology has been successfully used to provide increased thermal cycling and drop shock reliability in WLCSPs using a number of different methods that have been previously described. The method to be discussed in this paper is a production process using a screen printed, photo defined polymer system that does not require any in-process post cure.

Precise Chip Joint Method with Sub-micron Au Particle for High-density SiC Power Module Operating at High Temperature

In this work, a novel precise chip joint method using sub-micron Au particle for high-density silicon carbide (SiC) power module operating at high temperature is proposed. A module structure of SiC power devices are sandwiched between two silicon nitride-active metal brazed copper (SiN-AMC) circuit boards. To make a precise position and height control of the chip bonding, the top side (gate/source or anode pad side) of SiC power devices are flip-chip bonded to circuit electrodes using sub-micron Au particle with low temperature (250°C) and pressure-less sintering. The accuracy of the bonding position of chips was less than 10 μm and the accuracy of the height after bonding chips was less than 15 μm. Mechanical shear fatigue tests for flip-chip bonded SiC Schottky barrier diode (SBD) were carried out. As a result, initial shear strength of the joint was 36 MPa. The shear strength of 43 MPa is obtained after storage life test (500 hours at 250°C), and also 35 MPa is obtained even after thermal cycle stress test (1000 cycles between −40°C and 250°C). The flip-chip bonding of SiC-JFET is successfully realizedon the substrate without short or open failure electrically. Finally we joint the backside of the SiC-JFET (drain side) and the SiC-SBD (cathode side) to each circuit electrodes at once by means of reflow process with Au-12%Ge solder. The structured sandwich SiC power module was also successfully formed.

Cracking of a Tool Steel Guide Roller in a Bar Mill

Failure analysis of a guide roller used in a bar mill of an integrated steel plant has been presented. The guide rollers are positioned at the entry of rolling stands and act as guide in the multi-grooved pass for aligning the hot bars and hold the twisted oval bar while it enters a round pass. The hot bar is at a temperature of ≈1100°C, and the rollers are water cooled. The component is subjected to cyclic thermal stress depending on the mill operating conditions. The rollers are cracking longitudinally leading to failure. The investigation consists of visual inspection, chemical analysis, fractography, characterization of microstructures using optical and scanning electron microscopes (SEM), energy dispersive spectroscopy (EDS) analysis, and measurement of micro-hardness. The chemical analysis indicates the material as AISI D2 grade of cold work tool steel. Visual observation of the failed component shows multiple longitudinal cracks on the roller surface associated with a dark circular band of oxidation. The fracture surface shows a dark oxidized area propagating from the roller surface followed by flat bright appearance indicating final brittle fracture. Fractography of the dark surface from where the crack initiates shows fatigue striations. Microstructural examination under optical and SEM shows a network of coarse carbide particles at the grain boundary as well as uniformly distributed fine carbide precipitates within the martensite matrix. Multiple cracks are observed to initiate and propagate from the surface through the clusters of grain boundary carbides. EDS analysis and elemental mapping suggest the carbides to be chromium carbides. SEM shows micro-cracking of carbide particles associated with the crack. Clustered distribution of carbides deteriorates toughness and initiates cracking at the roller surface subjected to thermal cycling because of their differential thermal expansion coefficient leading to the failure of the component.