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The thermal incompatibility between fiber reinforced polymer (FRP) bars and concrete may cause splitting cracks within the concrete and, eventually, the deterioration of the bond between the FRP bar and the concrete. This paper presents a numerical study using ADINA finite elements software to investigate the thermal behavior of actual one-way concrete slabs reinforced with glass FRP (GFRP) bars varying the ratio of concrete cover thickness to FRP bar diameter (c/[d.sub.b]) from 1.3 to 2.8. Slabs are submitted to temperature variations varied from -50 to 60[degrees]C. The main results prove that first radial cracks occur in concrete, at the FRP bar--concrete interface, at thermal loads ([DELTA][T.sub.cr]) varied between 15[degrees]C and 30[degrees]C. While, the circumferential cracks appear within concrete, at FRP bar--concrete interface, at [DELTA][T.sub.cr] varied between -15[degrees]C and - 35[degrees]C depending of the ratio c/[d.sub.b] (1.3 to 2.8) and the tensile strength of concrete [f.sub.ct] (1.9 to 2.9 MPa). These numerical thermal loading values are relatively in good agreement with those predicted from the analytical model. The numerical model shows that there is no failure of the concrete cover for low temperatures for slabs having c/[d.sub.b] = 1.3 to 2.8 and [f.sub.ct] = 1.9 to 2.9 MPa. Nevertheless, for high temperatures, the splitting failure of concrete cover is produced at thermal loads [DELTA][T.sub.sp]' varied from 30[degrees]C to 59[degrees]C. While, for concrete situated between GFRP bars, the splitting failure occurred at thermal loads [DELTA][T.sub.sp]' equal to 46[degrees]C. Thermal stresses and strains, and also cracking thermal loads predicted from the numerical model are compared with those obtained from analytical models and experimental tests. Key words: glass fiber reinforced polymer (GFRP) bars, concrete slabs, numerical model, cracking thermal loads, thermal stresses and strains. L'incompatibilite thermique entre les barres de polymere renforce de fibres (<< FRP >>) et le beton peut causer des fissurations dans le beton et, finalement, la deterioration du lien entre la barre de FRP et le beton. Dans le cadre de cet article, on presente une etude numerique qui utilise le logiciel d'elements finis ADINA afin d'examiner le comportement thermique de dalles unidirectionnelles en beton renforce de barres de FRP de verre (<>) en variant le rapport entre l'epaisseur d'enrobage et le diametre de barre de FRP (c/[d.sub.b]) de 1,3 a 2,8. Les dalles sont soumises a des variations de temperature entre -50 et 60[degrees]C. Les principaux resultats prouvent que les premieres fissures radiales se produisent dans le beton, a l'interface barre de FRP/beton, aux charges thermiques ([DELTA][T.sub.cr]) variant entre 15 et 30[degrees]C. Tandis que, les fissures circulaires apparaissent dans le beton, a l'interface barre de FRP/beton, a [DELTA][T.sub.cr] variant entre -15 et -35[degrees]C en fonction du rapport c/[d.sub.b] (1,3 a 2,8) et de la resistance a la traction du beton [f.sub.ct] (1,9 a 2,9 MPa). Ces valeurs numeriques de chargement thermique concordent relativement bien avec celles prevues par le modele analytique. Le modele numerique montre qu'il n'y a aucune defaillance de l'enrobage a de basses temperatures pour des dalles ayant c/[d.sub.b] = 1,3 a 2,8 et [f.sub.ct] = 1,9 a 2,9 MPa. Neanmoins, a des temperatures elevees, la defaillance par fissuration de l'enrobage s'est produite a des charges thermiques [DELTA][T.sub.sp]' variant de 30 a 59[degrees]C. Tandis que, pour le beton se trouvant entre les barres de GFRP, la defaillance par fissuration s'est produite a des charges thermiques [DELTA][T.sub.sp]' egalent a 46[degrees]C. Les contraintes et les deformations thermiques et aussi les charges thermiques de fissuration prevues au moyen du modele numerique sont comparees a celles obtenues au moyen des modeles analytiques et des essais experimentaux. [Traduit par la Redaction] Mots-cles : barres en polymere renforce de fibres de verre (GFRP), dalles de beton, modele numerique, charges thermiques de fissuration, contraintes et deformations thermiques., 1. Introduction Corrosion is the term used to describe the deterioration of a material as it reacts with its environment and is a natural process that occurs when materials such [...]

In the present study, thermoelastic behavior of a semi-infinite rod, which is subjected to a time exponentially decaying laser pulse, is formulated. The rod is free at the left end and the laser pulse moves along the axial direction from the left end. The non-Fourier effect of the heat conduction equation is considered and the Laplace transformation method is employed in solving the governing equations. The temperature, displacement, strain, and stress in the rod are derived and the distributions of the parameters at different positions are analyzed. Also the influence of the laser speed is investigated. Key words: movable heat source, laser pulse, thermoelastic response, semi-infinite rod, non-Fourier effect. Nous presentons ici une formulation pour etudier le comportement thermo-elastique d'une tige semi-infinie soumise a une impulsion laser a decroissance exponentielle dans le temps. L'extremite gauche de la tige est fixee et l'impulsion se deplace axialement de la gauche vers la droite. Nous considerons l'equation de conduction non Fourier de la chaleur et nous utilisons la transformation de Laplace pour resoudre les equations directrices. Nous obtenons la temperature, le deplacement, l'effort et la deformation dans la tige et nous analysons la distribution des parametres a differentes positions. Nous regardons aussi l'influence de la vitesse du laser. [Traduit par la Redaction] Mots-cles : source de chaleur deplacable, impulsion laser, reponse thermoplastique, tige semi-infinie, effet non Fourier., 1. Introduction Boeing Company has developed a kind of high-energy laser weapon, which have successfully destroyed more than 150 target drones in three series of tests. This technology can be [...]

Tri-(butanediol-monobutyrate) citrate (TBBC) as a new plasticizer for poly(lactic acid) (PLA) was synthesized via a two-step esterification. The chemical structure of TBBC was characterized by ¹H-nuclear magnetic resonance. The studies on solubility parameters, transparence, and storage stability indicated the good miscibility between PLA and TBBC. The glass transition, crystallization, thermal, and mechanical properties of PLA plasticized by TBBC were evaluated. With an increase in TBBC content, the glass transition temperature ([T.sub.g]), melting point ([T.sub.m]), and the cold crystallization temperature ([T.sub.cc]) of plasticized PLA gradually shifted to a lower temperature. The elongation at break and flexibility were greatly improved by the addition of TBBC. After 30 days of storage, PLA plasticized with up to 20 wt% of TBBC exhibited good storage stability and remained the original transparence and mechanical properties. The flexibility of PLA/TBBC films can be tuned by changing TBBC content. The corresponding crystalline morphology and structure were investigated by Polarizing optical microscope and X-ray diffraction as well. This study revealed that TBBC was miscible with PLA and may therefore be a promising plasticizer for PLA-based packaging materials. POLYM. ENG. SCI., 55:205-213, 2015. [C] 2014 Society of Plastics Engineers, INTRODUCTION The environmental and food safety problems have aroused people's concern about biodegradable materials [1]. Biodegradable polymers are considered as food packaging materials to solve serious ecological problems caused by [...]

This paper discusses the microstructure evolution of copper (Cu) and gold (Au) ball bonds after various extended reliability stresses such as biased highly accelerated temperature and humidity test (HAST), unbiased highly accelerated temperature and humidity test (UHAST), temperature cycling (TC), and high temperature storage life (HTSL) in BGA package. Objective of this study is to study the microstructure evolution and changes after long hours and long cycles of component reliability stressing and its predicted failure mechanisms and to determine the long-term reliability comparison with combination of bonding wires in HAST, UHAST, and TC. Secondary electron microscopy (SEM) and energy dispersive X-ray (EDX) have been carried out to understand the respective microstructure of failed samples in HAST, UHAST, TC, and HTSL long-term reliability failures. Respective failure mechanisms of copper and gold ball bonds carrion under HAST and UHAST, ball bond lifting in TC and HTSL have been analyzed and proposed. The evolution of surface morphology, including copper and gold ball bond micro cracking, gold ball bond Kirkendall microvoiding and intermetallic compound (IMC) formation, was studied in FBGA package with copper and gold ball bonds during various reliability stresses. Biased HAST, UHAST, TC, and HTSL mechanisms were proposed to explain the observed morphological changes and the resulting ball bond wear out modes after extended reliability stresses. Weibull reliability analyses have been established to compare the performance of copper and gold ball bonds under humid and dry environmental tests. Keywords Microstructure evolution * Copper and gold ball bonds * Failure mechanisms * SEM * EDX analysis * Extended reliability * Weibull plot, Introduction Gold and copper wire bondings are two most common bonding techniques used in microelectronic packaging in semiconductor industry. Recently, copper wire bonding appears to be the alternate materials and [...]

Thermoelastic damping is a critical loss mechanism in micromachined resonators used for sensing and communication applications. In this paper, thermoelastic damping of the axisymmetric vibration of laminated circular plate resonators will be discussed. Based on the classical laminated plate theory assumptions, the governing equations of coupled thermoelastic problems are established for axisymmetric out-of-plane vibration of trilayered circular plate with fully clamped boundary conditions. The analytical expression for thermoelastic damping is obtained and the accuracy is verified through comparison with FEM results. Then the effect of material selection and the volume fraction of the covering layers are numerically evaluated. Finally, the thermoelastic damping for different vibration modes is also evaluated. PACS Nos.: 07.20.Dt, 46.25.Hf, 62.20.D-, 81.40.Jj, 65.40.De. L'amortissement thermo-elastique est un mecanisme critique de perte dans les resonateurs micro-usines utilises dans les applications de senseur et de communication. Nous etudions ici l'amortissement thermo-elastique des vibrations de symetrie axiale dans des resonateurs lamines circulaires. Sur la base de la theorie classique des plaques laminees, nous obtenons les equations directrices des problemes thermo-elastiques couples pour des vibrations a symetrie axiale hors plan de plaques circulaires tri-couches avec des conditions limites encastrees. Nous obtenons une expression analytique pour l'amortissement thermo-elastique et en verifions la precision en comparant les resultats avec ceux de FEM. Nous evaluons alors numeriquement l'effet du materiau selectionne et la fraction en volume des couches de recouvrement. Nous evaluons finalement l'amortissement thermo-elastique pour differents modes de vibration. [Traduit par la Redaction], 1. Introduction Miniaturized resonators are widely used as sensors and modulators in micro- and nanoelectromechanical systems [1-4]. For resonators, it is desired to design and construct systems with as little [...]

In the present paper, we introduce the coupled theory, Lord-Schulman theory, and Green-Lindsay theory to study the influences of a magnetic field and rotation on a two-dimensional problem of fiber-reinforced thermoelasticity subject to thermal loading by a laser pulse. The material is a homogeneous isotropic elastic half-space and is heated by a non-Gaussian laser beam with pulse duration of 8 ps. The method applied here is to use normal mode analysis to solve a thermal shock problem. Deformation of a body depends on the nature of the force applied as well as the type of boundary conditions. Numerical results for the temperature, displacement, and thermal stress components are given and illustrated graphically in the absence and the presence of the magnetic field, rotation, reinforcement, and for two different values of time. PACS Nos.: 81.05.Ni, 46.25.Hf, 62.20.D-, 81.40.Jj. Nous introduisons ici la theorie couplee, celle de Lord-Shulman et celle Green-Lindsay pour etudier l'influence d'un champ magnetique et de la rotation sur un probleme bidimensionnel de thermoelasticite d'un milieu renforce par fibres sujet a une charge thermique due a un laser pulse. Le materiau, un demi-espace elastique, isotrope et homogene, est chauffe par un faisceau laser non gaussien dont les impulsions durent 8 ps. Nous appliquons ici une methode de modes normaux pour resoudre le probleme de chocs thermiques. La deformation du milieu depend de la nature des forces appliquees et des conditions limites. Nous presentons nos resultats numeriques et les illustrons graphiquement pour la temperature, le deplacement et les composantes des efforts thermiques, avec et sans champ magnetique, rotation, renforcement et pour deux differentes valeurs du temps. [Traduit par la Redaction], 1. Introduction The linear theory of elasticity is of paramount importance in the stress analysis of steel, which is the commonest engineering structural material. To a lesser extent, linear elasticity [...]

Thermoplastic carbon fiber fabric reinforced composites (CFFRCs) were prepared using a novel fast manufacturing process with a low viscosity polymerizable cyclic butylene terephthalate (CBT) resin. Structure and properties of the composites altered by thermal annealing were investigated to develop appropriate post processing of the CFFRCs for fast production and lowering the processing cost. Annealing at 200°C for 120 min resulted in improved mechanical properties and thermal stability of the polymerized CBT (pCBT) based on differential scanning calorimetry, wide-angle X-ray diffraction, and thermo gravimetric analysis. The tensile strength of the CFFRC compression molded at 250°C for 2 min was 440 MPa and that of the CFFRC annealed at 200°C for 120 min after compression molding was 500 MPa, which is an improvement of 550 and 625% relative to the pCBT matrix, respectively. In addition, the thermal stability of the CFFRC annealed at 250°C for 120 min improved by 10°C. Therefore, tensile strength and thermal stability of the manufactured CFFRC can be improved by using the appropriate annealing conditions., INTRODUCTION Worldwide interest in energy reduction is increasing because of global issues, such as global warming, carbon emission, and inflation of oil prices, and weight savings in automobiles represent one [...]

Polypropylene/fumed hydrophilic silica nanocomposites were prepared via melt mixing method using a single-screw extruder. Comparative study with and without compatibilizing copolymer agent (maleic anhydride grafted polypropylene: PP-g-AM) was conducted. The obtained results were interpreted in terms of silica nanoparticle-silica nanoparticle and silica nanoparticle-polymer interactions. These results have shown that the addition of nanofillers improves the properties of the nanocomposites. From transmission electron microscopy, it was found that agglomerations of silica particles into the PP matrix increased in average size with increasing silica contents, except in presence of the copolymer. Storage modulus values of the nanocomposites measured by dynamic mechanical thermal analysis were sensitive to the microstructure of the nanocomposites. Higher silica contents resulted in higher storage modulus, revealing that the material became stiffer. By adding the compatibilizer, a further increase of storage modulus was observed due to the finer dispersion of the filler in the matrix and the increased interfacial adhesion. Crystallization rates were found to increase with the increase of silica nanoparticles as well as PP-gMA content. In addition, silica nanoparticles and the compatibilizing agent present centers of germination and nucleation of crystallites. Thus, the use of the coupling agent resulted in a further enhancement of mechanical properties of the nanocomposites due to the reduction of silica agglomeration., INTRODUCTION Over the past decades, there has been a notable progress in the science and technology of polymer nanocomposites. This innovative class of materials made up of organic polymer composites [...]

Integral abutment bridges accommodate thermal superstructure movements through flexible foundations rather than expansion joints. While these structures are a common alternative to conventional design, the literature on measured field stresses in piles supporting integral abutments appears to be quite limited. Therefore, field data from strain gauges installed on the abutment foundation piles of a 76 m long; two-span integral abutment bridge are the focus of this paper. Axial load, weak- and strong-axis bending moments of the foundation piles, as well as abutment movement and backfill response, are presented and discussed. Results indicate that the abutment foundation piles are bending in double curvature about the weak axis, as a result of thermal bridge movements, and bending also about the strong axis due to tilting of the abutments. A simple subgrade modulus approach is used to show its applicability in predicting behaviour under lateral loading. In the past, much emphasis has been placed on the lateral displacements of piles and less on variations of axial load. In this paper, a new hypothesis, which offers insight into the mechanisms behind the observed thermal variations in axial load, is proposed and assessed. The data from the field monitoring are also compared with the limited data reported in the literature. Key words: field monitoring, integral abutment bridge, axial load, pile moment, pile stress. Les culees de ponts integrales permettent les mouvements thermiques de la structure grace a des fondations flexibles plutot que par des joints d'expansion. Malgre que ces structures soient une alternative courante au concept conventionnel, la litterature sur les contraintes mesurees sur le terrain dans les pieux supportant les culees integrales semble limitee. C'est pourquoi cet article se penche sur des donnees de terrain de sondes de deformation installees sur des pieux de fondation-culee d'un pont a culee integrale de 76 m de long a deux voies. On presente et discute des charges axiales, des moments de torsion selon l'axe faible et fort des pieux de fondation, de meme que les mouvements de la culee et la reponse du remblai. Les resultats indiquent que les pieux de fondation-culee flechissent en courbure double selon l'axe faible en raison des mouvements thermiques du pont, et flechissent aussi selon l'axe fort en raison de l'inclinaison des culees. Une approche de module de sol simple est utilisee pour demontrer l'applicabilite de la prediction du comportement sous sollicitations laterales. Dans le passe, beaucoup d'emphase a ete mise sur les deplacements lateraux des pieux et moins sur les variations des charges axiales. Dans cet article, une nouvelle hypothese, qui offre des connaissances sur le mecanisme derriere les variations thermiques observees en chargement axial, est proposee et evaluee. Les donnees du suivi de terrain sont aussi comparees avec les donnees limitees disponibles dans la litterature. [Traduit par la Redaction] Mots-cles: suivi de terrain, culees de pont integrales, charge axiale, moment d'un pieu, contrainte d'un pieu., Introduction Thermal expansion and contraction of bridge structures has conventionally been accommodated through expansion joints. However, to ensure continued unrestricted movement of the superstructure, expansion joints require regular, and often [...]

A series of tensile and ratcheting experiments for cold compaction polytetrafluoroethylene (PTFE) and bronze filled PTFE (PTFE/bronze) were conducted with Dynamic Mechanical Analyzer (DMA-Q800) at room and high temperature (473 K). The effects of peak stress-holding time, creep, recovery, mean stress history, stress-rate history, and pretension on the ratcheting behavior of PTFE/bronze were investigated. It is found that longer peak stress-holding time leads to larger ratcheting strain accumulation. In the meantime, the ratcheting strain accumulates more rapidly at high temperature and the influence of temperature is more obvious than that of the additive fraction of bronze. Creep strain produced during the uploading and the stress-holding time only partially recovers in the unloading process. Moreover, prior lower stress rate enhances the deformation resistance and restrains the ratcheting of subsequent cycling at higher stress rate. The ratcheting strain in the subsequent cyclic loading at lower mean stress is also restrained by previous cyclic loading at higher mean stress. Finally, the elastic modulus increases and the ratcheting strain is restrained apparently after the pretension. In addition, the elastic modulus and ratcheting strain of the PTFE/ bronze with both pretension and recovery are smaller than those with pretension but without recovery., INTRODUCTION Polytetrafluoroethylene (PTFE) as a widely used engineering material is a synthetic fluoropolymer of tetrafluoroethylene. Due to its low coefficient of friction, excellent dielectric properties and chemical inertness, PTFE is [...]

Rice husk (RH) reinforced wheat gluten/glycerol (Gly/ Glut) and rice husk (R) reinforced wheat gluten-glycerol/chitosan-polyethylene glycol (Gly/Glut-CP) biocomposites with varying rice husk loading were prepared. Morphological, thermal, and mechanical properties of the biocomposites were investigated by scanning electron microscope, thermogravimetric analyzer, and tensile testing machine, respectively. Water absorption properties and surface functional groups of the biocomposite films were determined by weight measurement and attentuated total reflectance Fourier transform infrared spectroscopy, respectively. The results were discussed in terms of chitosanpolyethylene glycol (CP) and rice husk content. Although CP and 1-g rice husk addition decreased maximum degradation temperature of Gly/Glut film, adding of more rice husk did not considerably change the maximum degradation temperature. As a result of adding CP, the tensile strength of Gly/Glut film was increased by about 183%, whereas tensile modulus was decreased by about 34%., INTRODUCTION The increasing demand for eco-friendly and biodegradability materials, the growing global environmental awareness and environmental concern, high rate of depletion of petroleum resources, increase in petroleum prices, and new [...]

Laser melt electrospinning is a novel technology to fabricate scaffolds in the tissue engineering applications. The melt electrospinning is much safer than the conventional solution electrospinning due to without solvent effect. In this study, thermoplastic polyurethane (TPU) micro/nanofibers were successfully prepared by using this method. The effects of laser current and applied voltage on the fibers morphologies were investigated by scanning electron microscopy. The thermal behaviors and crystallization conditions of the TPU under different states were demonstrated by differential scanning calorimetry and X-ray diffraction analysis. The mechanical property and the specific surface area of the TPU fibers membranes were also studied. All the analysis results showed that the effects of laser current and applied voltage on the average fiber diameter were complicated, the average fiber diameter ranging from 1.70 to 2.53 nm; the TPU is not an easily crystallized material; the electrospun fibers exhibited an amorphous phase; the average elongation at break laser of the electrospun TPU fiber membranes is about 134%; the average tensile strength is about 1.02 MPa and the specific surface area of the electrospun TPU fiber membrane is about 199 [m.sup.2]/g. POLYM. ENG. SCI., 54:1412-1417, 2014. © 2013 Society of Plastics Engineers, INTRODUCTION The polymer fibers have been applied in many areas such as high-performance filters, membranes optics, vascular grafts, protective clothing, molecular templates, tissue scaffolds, and sensing applications due to owning [...]

In this study, [Ca.sup.2+]-crosslinked sodium alginate (SA) gel films (SA-Ca/SA2-Ca) have been prepared, and their structural and thermal characterizations were investigated using fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis, respectively. Dielectric characterization was performed at room temperature in the frequency range of 12 Hz-100 kHz. The equilibrium swelling value (ESV) of gel films was determined both in distilled water and in 0.1 M sodium chloride (NaCl) solution at room temperature. Sodium alginate films (SA/ SA2) were also prepared for use as reference. The effect of the crosslinking of sodium alginate on the dielectric and thermal properties of gel films was investigated by comparing the properties of gel films with those of SA/ SA2 films. Although ESV of [Ca.sup.2+]-crosslinked SA film in distilled water is about 350 [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] it decreased into one third in 0.1 M NaCl solution. The crosslinking of SA did not significantly affect the thermal properties, but it decreased the β-relaxation associated with the polar side groups. Frequency spectra of electric modulus, impedance and Cole-Cole plots confirmed the higher conductance values of SA-Ca films at low frequencies than those of SA film due to the presence of by-product of crosslinking., INTRODUCTION Sodium alginate (SA) is a low cost, environmentally safe, nontoxic, weak acidic, and an anionic, linear-chained natural polysaccharide. In recent years, it has gained more importance due to its [...]

The thermal, mechanical, and morphological properties of biobased thermoplastic starch (TPS) obtained from agricultural waste seed (AWS) and agricultural waste tuber (AWT) blended with polypropylene (PP) were investigated in this article. The grounded (pulverized) AWS and AWT were different in amylose/amylopectin ratios and contained relatively low starch content (≤ 50%). The commercial grade of TPS (CS) and native tapioca starch blended PP (NTS/PP) were also prepared for comparison. The performances of the TPS/ PP blends were dependent on the starch composition (e.g., amylose-to-amylopectin ratio), particle size, dispersion, and interfacial adhesion with matrix. The high-amylopectin starch blend (i.e., AWS/PP) was more susceptible to thermal degradation than the amylose-rich material (i.e., NTS/PP). The addition of starch to PP not only led to a stiffening effect (i.e., increase in storage modulus), but it also affected the relaxation of polymer matrix by shifting the thermal transition (i.e., glass transition temperature) to a higher temperature. POLYM., INTRODUCTION Biobased product is a product containing in whole or partly made from renewable resources according to definition in ASTM D6852. ASTM D6866 is the standard test method for biobased [...]

Ochre (Oc), with its high absorption and viscous properties and presence of several inorganic components, was incorporated in a polycarbonate-unmodified carbon nanotubes using processing methods such as electrospinning and compression molding, to produce strong and flame resistant composites with biaxially oriented nanomaterials. These composites were found to have good mechanical properties (ultimate tensile strength of ~95.3 MPa) and flame resistance (~464 J [g.sup.-1] [K.sup.-1] heat release capacity) when ~1 wt% of single-walled carbon nanotubes was used with 2.5 wt% Oc, which was used as a compatibilizer and flame retardant., INTRODUCTION Effective reinforcement of a polymer matrix requires resolution of two classic problems as follows: (1) the tendency of reinforcing agents to agglomerate uncontrollably in the matrix polymer and (2) [...]

This study is carried out on the effect of processing conditions including preparation methods, ultrasonication, film thickness, and thermal annealing on the thermal, mechanical, and piezoelectric properties of copolymer of poly(vinylidene difluoride-trifluoroethylene) (P(VDF-TrFE)J. Free-standing films and films on substrates are prepared by solvent casting and spincoating, respectively. The results obtained by differential scanning calorimetry show that the Curie transition of the copolymer films was influenced by the preparation methods, with very little difference in the melting transition. The difference was attributed to a less uniform distribution of TrFE comonomer units within the crystalline and amorphous regions of the spin-coating films. However, no effect of the preparation methods on the piezoelectric properties of the films was observed. It is also found that the short ultrasonication, film thickness higher than critical value of crystallization of P(VDF-TrFE) (about 100 nm), and drying before annealing did not have a significant effect on the properties of the films. Surprisingly, the ultrasonication had a clear impact on the relaxations at high temperature of the polymer chains. In addition, this study indicates that a short annealing by 10 min at 140°C was enough to obtain well-crystallized films, which is interesting from the industrial point of view., INTRODUCTION Since the discovery of its strong piezoelectric activity in 1969 by Kawai [1], poly(vinylidene fluoride) (PVDF) and its copolymers, in particular the copolymers of vinylidene difluoride and trifluoroethylene P(VDF-TrFE) [...]

The present paper attempts to investigate the propagation of plane waves in an isotropic elastic medium under the effect of initial stress and temperature-dependent properties. The modulus of elasticity is taken as a linear function of reference temperature. The formulation is applied under the thermoelasticity theory with three-phase-lag, proposed by Choudhuri (J. Thermal Stresses, 30, 231 (2007)). Normal mode analysis is used to obtain the expressions for the displacement components, the temperature, the stress, and the strain components. Numerical results for the field quantities are given in the physical domain and illustrated graphically. Comparisons are made with the results predicted by different theories (Lord-Shulman theory, the theory of thermoelasticity type III, and the three-phase-lag model) in the absence and presence of the initial stress as well as the case where the modulus of elasticity is independent of temperature. PACS Nos.: 46.25.Hf, 62.20.D-, 81.40.Jj. Nous etudions ici la propagation d'ondes planes dans un milieu elastique isotrope et leur dependance sur la charge initiale et les proprietes qui varient avec la temperature. Nous prenons pour acquis que le module d'elasticite est une fonction lineaire de la temperature de reference. Nous appliquons la theorie de la thermo-elasticite avec trois retards de phase, proposee par Choudhuri (J. Thermal Stresses, 30, 231 (2007)). L'analyse en modes normaux nous permet d'obtenir les expressions pour les composantes du deplacement, la temperature, la charge et les deformations. Nous presentons les resultats numeriques pour les champs dans le domaine physique et les illustrons graphiquement. Nous comparons ces resultats avec ceux d'autres theories (la theorie de Lord-Shulman, la theorie de la thermo-elasticite de type III et le modele a trois retards de phase), en presence et en absence de charge initiale, et lorsque le module d'elasticite est independant de la temperature., 1. Introduction Generalized theories of thermoelasticity have been developed to overcome the infinite propagation speed of thermal signals predicted by the classical coupled dynamical theory of thermoelasticity [1]. The subject [...]

In this article, high-density polyethylene/ethylene vinyl-acetate copolymer (HDPE/EVA) composites filled with two different particle sizes (45 and 150 µm) of expandable graphite (EG) were prepared by using a twin-screw extruder. The thermal stability, flammability, and mechanical properties of HDPE/EVA/EG composites were investigated by thermogravimetric analysis (TGA), cone calorimeter test (CCT), tensile test, and scanning electron microscopy (SEM). The results from TGA and CCT indicated that EG significantly enhanced the thermal stability and fire resistance of HDPE/EVA blend. The thermal stability and flame retardancy of HDPE/ EVA/EG composites were improved with decreasing particle size of EG. Although the onset of weight loss of the flame-retardant composites occurred at a lower temperature than that of HDPE/EVA blend, the flame-retardant composites produced a large amount of char residue at a high temperature. The consolidated char layer formed a barrier, which could reduce heat, low-molecular transfer, and air incursion, and thus enhanced the flame retardancy. The data from the tensile test showed that the addition of EG deteriorated the mechanical properties; however, the tensile stress and strain of HDPE/EVA/EG composites increased with decreasing the particle size of EG owing to the strong interface adhesion between polymer matrix and inorganic particles. POLYM. ENG. SCI., 54:1162-1169, 2014. © 2013 Society of Plastics Engineers, INTRODUCTION Polyethylene (PE) is one of the most widely used polymeric materials owing to its low cost, balanced mechanical properties, good processability, and so on [1-3]. However, there are some [...]

Different montmorillonites either, completely hydrophilic (Mont-O), amphiphilic (Mont-25, Mont-50, and Mont-75) or completely hydrophobic (Mont-100) were used as reinforcing fillers for styrene butadiene rubber (SBR) and acrylonitrile butadiene rubber (NBR) [...]

Nanocomposites based on isotactic polypropylene (tPP) and titanium dioxide ([TiO.sub.2]) nanoparticle containing 1-15 vol% (4.6-45.5 wt%) of the nanoparticle were prepared by the melt blending process. The effect of an [...]

This work was aimed at studying the effects of incorporation of epoxidized soybean oil (ESO) in a standard bisphenol A-type epoxy resin (EP) cured by anhydride hardener. The EP ESO [...]

A novel di-carboxyiic acid curing agent (DACA) was successfully synthesized and cured with three different epoxy resins: glycidyl end-capped poly(bisphenol-A-coepichlorohydrin) (pDGEBA, [M.sub.n] 377), N,N-diglycidyl-4-glycidyloxyaniline (TGAP), and 4,4'-methylenebis(N,N-diglycidylaniline) (TGDDM). The cured epoxy exhibited excellent thermal stability, which was indicated by high initial degradation temperature ([T.sub.id]) and char yield. The [T.sub.id] values of cured epoxy were in the range of 327-338°C, and the char yields increased with increasing epoxy functionality. The char yields of cured DACA/ pDGEPA, DACA/TGAP, and DACA/TGDDM samples were 21.1, 60.4, and 66.9%, respectively. In addition, the cured epoxy samples also showed low coefficients of thermal expansion and high storage moduli (E'), which were around 60 ppm/°C and 2800 MPa, respectively. The failure surfaces were ductile and rough, so the cured epoxy samples are expected to have high fracture toughness and impact strength. POLYM. ENG. SCI., 54:695-703, 2014. © 2013 Society of Plastics Engineers, INTRODUCTION Epoxy resins are a versatile group of thermoset polymers that have excellent properties, such as stiffness, strength, chemical resistance, low dielectric constant and loss, adhesiveness to substrates, and thermal [...]

Rolling process was carried out with extruded polypropylene as crystalline polymer at various rolling temperatures, and the rolling characteristics, cross-section morphologies, and tensile properties were investigated. The rolling characteristics were evaluated by springback and dimensional change. The springback increased with increasing rolling temperature. The increment of length was larger than that of width because of the influence of uniaxial drawing by rotation of the rollers. Uniform morphologies were observed at a rolling ratio of 70% and a rolling temperature of 23°C. In contrast, molecular orientation near the surface was higher compared with the inner part when rolled at 70°C. Furthermore, micro spherulitic structures were observed near the surface where recrystallization occurred because of the rising temperature on the specimen surface by friction. Therefore, different morphologies appeared near the surface and in the inner part. Tensile strength was obtained for the rolling direction when rolled at 110°C lower than at other rolling temperatures. It was likely that the molecular orientation was decreased by increasing the spring-back when rolled at high temperature. POLYM. ENG. SCI., 53:2573-2581, 2013. © 2013 Society of Plastics Engineers, INTRODUCTION It is widely known that morphologies such as crystalline structure, molecular orientation, and crystallinity influence mechanical properties. For example, the properties of polymer materials are enhanced by high molecular [...]

The morphological, mechanical, thermal, and tribological properties of high-density polyethylene (HDPE) composites reinforced with organo-modified nanoclay (3 and 6 wt%) were studied. A commercial maleic anhydride-based polymeric compatibilizer (PEgMA) was used to improve the adhesion between the polyethylene and clay. Transmission electron microscopy (TEM) characterization of composites revealed that nanoclay exists mainly in a multilayered structure in the HDPE matrix. Mechanical testing of composites showed that Young's modulus and tensile strength increased with nanoclay content. Coefficients of the linear thermal expansion (CLTE) of HDPE-PEgMA-clay composites were slightly lower in the flow direction than those of HDPE-PEgMA. The tribological properties were measured in dry conditions against a steel counterface. The friction coefficient of the matrix was decreased by the addition of clay. Electron microscopic results suggested that the wear mechanism for HDPE and HDPE composites was mainly adhesive. Clay agglomerates were observed on the worn surfaces of the composites, which may partly explain decreased friction. POLYM. ENG. SCI., 53: 1279-1286, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION Polyethylene is a widely used semicrystalline polyolefin that possess a good chemical resistance, low cost, easy processability, and moderate mechanical properties (1). Traditionally, the properties of polymers have been [...]

Polyacrylonitrile (PAN) fibers were heated and stretched in a steam bath mixed with nitrogen in the early stage of stabilization. During this process, the flexible linear chain of PAN molecule was converted to a rigid ladder structure by intramolecular cyclization. The shrinkage tension along the fiber axis decreased during this heat treatment, because water molecules here acted as a plasticizer for stretching. Consequently, the preferred orientation of ladder molecules in the stabilized fibers was enhanced. As a result, the preferred orientation, crystallite dimensions, and mechanical properties of the resultant carbon fibers (CFs) and graphite fibers (GFs) were improved, comparing with the corresponding CFs and GFs without pretreatment in the steam bath. POLYM. ENG. SCI., 53:827-832, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION The preferred orientation of crystallites along the fiber axis is one of the most important structure parameters for carbon fibers (CFs). Higher preferred orientation usually gives rise to higher [...]

Temperatures were measured along instrumented geogrids to determine thermal strains and their changes with seasonal temperatures. It was observed that the application of temperature correction to the measured strain values by electrical wire resistance (EWR) strain gauges to compensate for temperature-induced strains is not correct. Because of the effects of soil confinement, the geogrids confined with soil do not undergo thermal expansion or contraction from temperature change if slippage between the soil and geogrid cannot occur. Instead of thermal strains, thermal stress or thermal force will be developed in the geogrids with the magnitude depending on the elastic properties, temperature change, and linear coefficient of thermal expansion. Key words: geogrid, strain gauge, temperature, thermocouple, thermal strain, thermal stress. Les temperatures ont ete mesurees le long de geogrilles instrumentees afin de determiner les deformations thermiques et leurs variations selon les variations saisonnieres des temperatures. Il a ete observe que l'application de la correction pour compenser les deformations induites par la temperature sur les mesures de deformations realisees avec des jauges de deformations par resistance du fil electrique (RFE) n'est pas correcte. En raison des effets de confinement du sol, les geogrilles confinees a l'interieur du sol ne subissent pas d'effets d'expansion ou de contraction thermique lorsque la temperature change s'il n'y a pas de glissement entre le sol et la geogrille. Plutot que des deformations thermiques, des contraintes ou forces thermiques seront developpees dans la geogrille, a des magnitudes dependant des proprietes elastiques, des variations de temperature et du coefficient lineaire d' expansion thermique. Mots-cles : geogrille, jauge de deformation, temperature, thermocouple, deformation thermique, contrainte thermique. [Traduit par la Redaction], Introduction The first author performed a research graduate thesis in 2003 on the long-term performance of a geogrid-reinforced test embankment constructed in 1986. Vertical and horizontal inclinometers and extensometers, settlement [...]

The wave nature of the heating model is considered, incorporating the Cattaneo equation with the presence of a volumetric heat source. The volumetric heat generation resembles the step input laser short-pulse intensity. The governing of the heat equation is solved analytically using the Laplace transformation method. The stress field generated due to thermal contraction and expansion of the substrate material is formulated and the closed-form solution is presented. It is found that the wave nature of the heating is dominant during the period of the irradiated short-pulse; however, in the late cooling period, the wave nature of heating is replaced by diffusional heat conduction, governed by Fourier's law. The stress field during the heating cycle is compressive and becomes tensile in the cooling cycle. PACS No: 44.10.+i Nous etudions la nature ondulatoire du modele de chauffage incorporant l'equation de Cattaneo, avec la presence de la source volumique de chaleur. La generation volumique de chaleur ressemble a intensite d'un laser a impulsion courte avec signal d'entree en echelon. Nous solutionnons analytiquement l'equation gouvernante de la chaleur en utilisant la methode de la transformation de Laplace. Le champ de contrainte genere par la contraction et l'expansion thermique du materiel du substrat est mis en formule et nous en presentons une solution analytique. Nous trouvons que le caractere ondulatoire du chauffage est dominant pendant la periode d' irradiation en impulsion courte, mais la conduction de chaleur de Fourier par diffusion domine la periode du refroidissement. Le champ de contrainte est en compression pendant le chauffage, mais en etirement pendant le refroidissement. [Traduit par la Redaction], 1. Introduction In short-pulse laser heating of metal surfaces, the absorption depth is small and the heating time is short. This results in a heat wave propagatiing at finite speed [...]

Understanding how communities respond to changes in temperature is a major challenge for community ecology. Temperature influences the relative degree to which top-down and bottom-up forces structure ecological communities. In greenhouse experiments using the aquatic community found in pitcher plants (Sarracenia purpurea), I tested how temperature affected the relative importance of top-down (mosquito predation) and bottom-up (ant carcasses) forces on protozoa and bacteria populations. While bottom-up effects did not vary consistently with temperature, the top-down effects of predators on protozoa increased at higher temperatures. These results suggest that temperature could change the relative importance of top-down and bottom-up effects in ecological communities. Specifically, higher temperature may increase the strength of top-down effects by raising predator metabolic rate and concomitant processes (e.g., activity, foraging, digestion, growth) relative to cooler temperatures. These findings apply broadly to an understanding of trophic interactions in a variable environment and are especially relevant in the context of ongoing climate change. Key words. food web; laboratory experiment; predation; temperature; top-down vs. bottom-up forces; Wyeomyia smithii.

The assumption of a linear temperature change through the slab depth has been overwhelmingly used in pavement analysis since Westergaard proposed a curling solution for rigid pavements. However, the actual temperature profiles through the slab thickness are primarily nonlinear. These nonlinear temperature profiles produce stresses that can be divided into three components: a uniform temperature stress, an equivalent linear curling stress, and a nonlinear self-equilibrating stress. It is the self-equilibrating stress component that often goes unaccounted for in concrete pavement stress prediction and can significantly affect the tensile stress magnitude and critical location. This paper presents a solution for a piecewise method and proposes a simplified method termed NOLA, or nonlinear area, that easily captures the effect of temperature nonlinearity on rigid pavement responses. The proposed NOLA method enables the use of a three-dimensional temperature frequency distribution that allows simple postprocessing of rigid pavement curling stress solutions derived from a linear temperature assumption. The impact of accounting for self-equilibrating stresses in terms of projected fatigue damage levels and critical cracking locations is also explored using a mechanistic-based rigid pavement analysis program called RadiCAL. DOI: 10.1061/(ASCE)TE.1943-5436.0000130 CE Database subject headings: Temperature effects; Fatigue; Damage; Stress; Concrete pavements. Author keywords: Non-linear temperature; Curling; Fatigue damage; Self-equilibrating stress; Built-in curl.

Shear connections are common connection types and they are designed to resist only shear loads. In a fire event, the axial restraint provided by adjacent structure creates unanticipated compressive and tensile forces in the beam and thus the connection. Using finite-element models, this study examines single-plate shear connections that are bolted to the beam and welded to the supporting girder. A floor subassembly, which includes the beam, girder, slab, and connection, is modeled so that appropriate forces are applied to the connection. The model is validated with the experiments of bolted lap splice plates at elevated temperatures, as well as full-scale experiments. This paper (1) illustrates efficient modeling methods for these floor subassemblies; (2) evaluates the importance of the slab in the connection response; and (3) examines the effects of the rate of heating and cooling on the connection. The results show that care needs to be taken as to how the concrete slab is represented in the model. The heating and cooling rates affect the beam stress distribution, peak temperatures, and peak displacements, but not the peak beam axial force. Also, the cooling phase creates large tensile forces in the connection which can lead to failure. DOI: 10.1061/(ASCE)ST.1943-541X.0000179 CE Database subject headings: Finite element method; Contacts; Connections; Fites; Steel. Author keywords: Finite element; Contact; Connection; Fite; Steel.

ABSTRACT Waste printed circuit boards (PCBs) are the focal points for handling electric and electronic waste. In this paper, a thermal shock method was used to pretreat waste PCBs for [...]

Laser fabrication of cooling holes in certain parts of the aero-engine components involves percussion or trepan drilling at acute angles (e.g., 16-30 deg) to the surface. These parts are often covered with plasma sprayed ceramic thermal barrier coatings (TBCs) to protect them from reaching excessive temperatures in hot engine environments. Delamination of the TBC is the main problem of laser drilling acute angled holes in the coated components. The present study investigates the mechanisms involved in the development of the delamination cracks. A significant role of melt ejection in the formation of cracks and the delamination at the coating/coating interface of the leading edge of a laser-drilled inclined hole was identified. It is shown that the delamination mechanisms at the TBC coating/bond coating and the bond coating/substrate interfaces are different. Melt ejection induced stresses were identified as the key mechanisms for the former type, while the thermal effects dominates the latter type. [DOI: 10.1115/1.4000102] Keywords: laser drilling, thermal barrier coating, delamination

Initiatives are underway to implement the new mechanistic-empirical pavement design guide (MEPDG) in Iowa. This paper focuses on the sensitivity study of jointed plain concrete pavements (JPCP) and continuously reinforced concrete pavements (CRCP) in Iowa using the MEPDG software. In this comprehensive study, the effect of MEPDG input parameters on the rigid pavement performance is evaluated using the different versions of the MEPDG software (0.7, 0.9, and 1.0) available to date. Representative JPCP and CRCP sections in Iowa were selected for analysis. Based on the sensitivity plots obtained from the MEPDG runs, the design input parameters were categorized as being most sensitive, moderately sensitive, or least sensitive in terms of their relative effect on distresses. In this study, the curl/warp effective temperature difference, the PCC coefficient of thermal expansion, and PCC thermal conductivity had the greatest impact on the JPCP and CRCP distresses. Compared to the original version of MEPDG software (Version 0.7), the updated versions (Versions 0.9 and 1.0) are more sensitive to inputs, which shows the evolution of engineering reasonableness. DOI: 10.1061/(ASCE)TE.1943-5436.0000036 CE Database subject headings: Pavement design; Rehabilitation; Sensitivity analysis; Rigid pavements; Iowa.

Aircraft structure subjected to elevated temperature presents a challenging design environment as damaging thermal stress can result. Thermal stress in a structural component is typically alleviated by accommodating the thermal expansion. However, very little work has been done that directly addresses the situation where such a prescription for expansion is not possible. When a structural component is failing due to tensile stresses which are thermally induced, the answer to the question of how best to stiffen the structure in this environment is far from trivial. This work demonstrates that conventional stiffening techniques, for example, thickness increase, may actually increase the rate of damage, as well as generate additional load that must be reacted by sub- and surrounding structure. Because flat plates represent a common structural element that is susceptible to developing tensile stresses due to thermally induced out-of-plane deformation, a simple strip model which represents cylindrical bending in a semi-infinite flat plate is chosen as the focus of this work.

This paper presented the stress distribution in a thick walled cylinder under thermal shock. Dirac function was introduced to model thermal shock. An analytical solution of the temperature field was obtained by Laplace transform. Based on the temperature solution, the thermal stress response of the thick walled cylinder was solved. The time dependent variations of the temperature field--thermal stress field--were discussed, and the effect of cylinder radius ratio on the problem was given. The exploration in this paper will lay a theoretical reference to further study on the decrease in fatigue damage of the superhigh pressure tubular reactor under thermal shock. [DOI: 10.1115/1.3066882] Keywords: thermal shock, thick wall cylinder, thermal stress, ultrahigh pressure tubular reactor

The interaction integral method that is equipped with the nonequilibrium formulation is generalized to evaluate the nonsingular T-stress as well as mixed-mode stress intensity factors in orthotropic functionally graded materials under thermomechanical loads. This paper addresses both Mode-I and mixed-mode fracture problems and considers various types of orthotropic material gradation. The orthotropic thermomechanical material properties are graded spatially and integrated into the element stiffness matrix using the direct Gaussian formulation. The types of orthotropic material gradation considered include exponential, power-law, and hyperbolic-tangent functions, and the numerical formulation is generalized for any type of smooth material gradation. The T-stress and mixed-mode stress intensity factors are evaluated by means of the interaction integral method developed in conjunction with the finite element method. The accuracy of numerical results is assessed by means of thermomechanically equivalent problems. [DOI: 10.1115/1.2936234] Keywords: functionally graded material (FGM), thermal fracture, stress intensity factor (SIF), T-stress, interaction integral, finite element method (FEM)

Despite enormous progress in laser aided direct metal/material deposition (LADMD) process many issues concerning the adverse effects of process parameters on the stability of a variety of properties and the integrity of microstructure have been reported. Comprehensive understanding of the transport phenomena and heat transfer analysis is essential to predict the thermally induced stresses in the deposited materials. A complete model that provides a quantitative relationship between process parameters, temperature history, phase transformation kinetics, and the thermal stresses is highly desirable. This paper examines the effect of deposition patterns and phase transformation kinetics on induced thermal stresses. The proposed model is based on the metallo-thermomechanical theory for sequentially coupled temperature, phase transformation, and stress/strain fields. Finite element analysis of various deposition processes illustrates the significant effect of deposition patterns on induced thermal stresses. Raster scan, spiral in-to-out, and spiral out-to-in patterns, in conjunction with their experimental verification, have been discussed in this paper. The existing model can easily accommodate any deposition pattern a user may want to study with slight modifications. The effect of substrate preheating on thermal stress is also studied and some reductions in thermal residual stress were observed. The importance of considering phase transformation effects is also verified through the comparison of the magnitudes of residual stresses with and without the inclusion of phase transformation kinetics. The simulation has been carried out for H13 tool steel deposited on a mild steel substrate. [DOI: 10.1115/1.2401620]

This paper describes the 'thermal opening technique' for enhancing the ultrasonic response of a tightly closed crack. In this approach, thermal stress is generated by cooling the part locally to reduce the crack closure stress in stainless steel plate, which improves sensitivity to detect the scattering wave from the crack surface; this has however not been successful by the usual ultrasonic inspection technique without introducing the thermal stress. It has been observed that the enhancement of the scattering wave continues for several hours after removing the thermal stress. This valuable and unique characteristic of the scattering wave is related to the change in the contact condition between the mating crack surfaces. Finally, a method is proposed for the evaluation of the depth of tightly closed crack from the difference in the time-of-flight between the scattering wave and the corner echo. The quantitative characteristic of the method is also verified experimentally. [DOI: 10.1115/1.2389026] Keywords: ultrasonic inspection, closed crack, scattering wave, signal enhancement, thermal stress

Repeated thermal shock cracking is common in the operation of pressure equipment where water and steam are present. Surprisingly, it is not fully covered in the ASME Boiler and Pressure Vessel code nor in fitness-for-purpose recommended practice such as API 579. An example of thermal shock stresses occurs when hot surfaces are exposed to splashing of cold water. This eventually may lead to crack nucleation and crack growth. However, not all thermal shock cracks lead to failures (such as rupture, leak, or, in more brittle material, fragmentation), indeed the most frequent situation is that the cracking arrests at a depth of a few millimeters. This paper presents a unique experimental study and analysis of the information being gained from this study in terms of design guidelines and crack growth mechanisms. In the experiments, cracks are initiated and then grown in low carbon steel specimens exposed to repeated thermal shock. The test-rigs achieve large thermal shocks through the repeated water quenching of heated flat plate specimens. The effect of steady state loads on the growth and environmental effects due to the aqueous nature of the testing environment are found to be major contributors to the crack growth kinetics. The most important findings are that the conditions leading to both the initiation and the arrest of cracks can be identified and that the depth of a starter notch contributes little to the crack propagation. [DOI: 10.1115/1.2389029] Keywords: thermal shock, cracking, initiation, growth, arrest, design, fitness for purpose

In this work, a gouged section of 1080 railroad rail steel is examined using metallographic techniques to characterize the nature of the damage. The gouging was performed by a rocket sled at Holloman Air Force Base, riding on VascoMax 300 steel shoes at 2.1 km/s. The damaged rail is evaluated in detail to examine material phase changes, shear bands, and heat effects. The results are compared to samples of the virgin material, machined and prepared exactly as they are prior to the Holloman AFB High Speed Test Track (HHSTT) runs. The gouged section was examined using optical microscopy, scanning electron microscope (SEM), and other techniques. The resulting microstructure is presented and compared to the virgin material. Material mixing, shear band formation, and significant thermal damage, consistent with a high energy gouging event, are confirmed. In addition, the material phase change evident in this approach allows us to estimate the thermal conditions present during the formation of the gouge. This thermal history, establishes a profile by which related research in gouge simulation can be validated against. A one-dimensional heat conduction model is presented that validates the cooling rates required to generate the presented microstructure. [DOI: 10.1115/1.2389030]

Approximate solutions were derived for the transient through steady-state thermal-stress fields developed in thick-walled vessels subjected to a potentially arbitrary thermal shock. In order to accomplish this, Duhamel's integral was first used to relate the arbitrary thermal loading to a previously derived unit kernel for tubular geometries. Approximate rules for direct and inverse Laplace transformations were then used to modify the resulting Volterra equation to an algebraically solvable and relatively simple form. The desired thermoelastic stress distributions were then determined using the calculated thermal states and elasticity theory. Good agreement was seen between the derived temperature and stress relationships and earlier analytical and finite-element studies of a cylinder subjected to an asymptotic exponential heating on the internal surface with convection to the outer environment. It was also demonstrated that the derived relationships can be used to approximate the more difficult inverse (deconvolution) thermal problem for both exponential (monotonic) and triangular (non-monotonic) load histories. The use of polynomial of powers [t.sup.n/2] demonstrated the feasibility, of employing the method with empirical data that may not be easily represented by standard functions. For any of the direct and inverse cases explored, the resulting relationships can be used to verify, calibrate, and/or determine a starting point for finite-element or other numerical methods. [DOI: 10.1115/1.2389002]

A Railgun-concept for the launch of small payloads into low-Earth orbits is currently under investigation. The first major project milestone foresees a 32-MJ railgun system able to launch nonpropelled projectiles with experiments for high-atmospheric research to an altitude of 115 km. This will be followed by a system to launch single-stage rocket-propelled projectiles to put in orbit nanosatellites using a 3.4-GJ railgun with a length of 180 m. One of the main issues to be investigated is the extreme thermal conditions the projectile's surfaces are exposed to, namely high temperatures and high thermal loads. These are caused by friction and turbulent flow properties, when the projectile rushes through the dense Earth's atmosphere in less than 30 s. The important questions to be answered for the design of a hypersonic projectile are the determination of the duration, magnitude, and location of the maximum temperatures with respect to the projectile's surface and its corresponding internal structure. For the determination of the complicated physical conditions, a two-step approach is used. In a so-called predesign phase, the HF3T code of the DLR is applied to estimate time-dependent temperature changes on the projectile's surface and/or within the material's structure as a function of the trajectory parameters. Finally, the three-degree-of-freedom trajectory program TRAJECTORY 3D of DLR is used to generate a detailed time-dependent data set, which includes the values for projectile velocity, Mach and Reynolds numbers, and atmospheric properties as a function of altitude. This data set is exchangeable with the TAU code of DLR for the solution of the Navier--Stokes equations, enabling pseudo-unsteady flow solutions along the trajectory. The solutions resulting from both approaches are then compared with emphasis on the surface temperature distributions. This strategy allows the verification of the feasibility of the proposed design solution for the railgun launched hypersonic projectiles. Index Terms--Aerothermodynamics, coupled calculations, heat load, railgun, unsteady flow.

The throat region of solid armatures is subjected to significant stress and temperature during a railgun launch. Recovered aluminum alloy armatures show evidence of plastic deformation, melting, and even cracking in the throat region. Plastic deformation can result from magnetic pinch or thermal expansion forces and melting from ohmic heating. Although cracking is historically associated with grain boundary melting, the cracks observed in recently recovered armatures are likely a result of thermal stresses. Finite-element codes EMAP3D and DYNA3D were linked to assess stresses generated by magnetic forces, inertial loading, wear, and thermal expansions. For low-speed armatures, thermal stresses were found to be as important as magnetic stresses. The observed cracking is likely due to rapid cooling, similar to quench cracking, and may or may not occur during launch. Index Terms--Cracking, solid armatures, throat region.

This paper summarizes experiments to investigate the possibility of delaying the onset of transition by using armatures with high melting temperatures. The rationale for the experiments was that armature materials with high melting points might outperform aluminum by reducing melting and erosion at the rail--armature interface. The tests used a novel technique that consists of placing thin claddings on the rail-contacting surfaces of the armatures. Two low-speed tests with copper armature claddings proved that claddings affixed to the trailing arms can survive a railgun launch. These tests were followed by four tests at about 2 km/s that used titanium armature claddings. These tests showed that titanium-clad armatures can perform well; however, this performance cannot be maintained beyond the first shot because the titanium armature claddings cause significant damage to the rails. Index Terms--Armature, cladding, railgun, titanium, transition to arcing contact.

Insights from recovered armatures suggest re-examining historical modeling assumptions for railguns. The finite-element codes EMAP3D and DYNA3D were linked to explore the effects of temperature-dependent material properties, thermal diffusion, armature wear, inertial loading, thermal stresses, and 2-D model approximations. Temperatures and principal stresses for each of these cases were compared. Thermal diffusion and thermal stresses in armatures cannot be ignored past the first millisecond of launch; material properties under pulsed heating can significantly differ from equilibrium and room-temperature values. Armature wear and inertial loading can be ignored at low speeds, but not at high speeds (>1 km/s). Models in 2-D can approximate 3-D models with appropriate boundary conditions, but only for the first few milliseconds of launch. With a detailed EMAP3D model and minimal assumptions, simulations that agree within a few percentage points of microstructural measurements from recovered armatures are possible. Index Terms--Model assumption, railguns.

We present a finite-element-based analysis to determine if there are potential reliability concerns due to thermally induced stresses in interwafer copper via structures in three-dimensional (3-D) ICs when benzocyclobutene (BCB) is used as the dielectric adhesive to bond wafers. We first partially validate our approach by comparing computed results against two types of experimental data from planar ICs: 1) volume-averaged thermal stresses measured by X-ray diffraction in an array of parallel Cu lines passivated with TEOS and 2) studies of failures induced by thermal cycling via chain structures embedded in SiLK or SiCOH. In the volume-averaged thermal stress study, predicted stress slopes (d[sigma]/dT) agree well with other modeling results. Our computed stress slopes agree reasonably well with experimental data along the Cu line direction and normal to the Cu lines surface, but we underestimate the stress slope across the Cu line. In the case of via chains, computed von Mises stresses agree with the results of thermal cycle experiments; we predict failure when SiLK is used as a dielectric and predict no failure when SiCOH is used as the dielectric. The approach is then employed to study thermal stresses in interwafer Cu vias in 3-D IC structures bonded with BCB. Simulations show that the von Mises stresses in interwafer Cu vias decrease with decreasing pitch at constant via size, increase with decreasing via size at constant pitch, and decrease with decreasing BCB thickness. We conclude that there is a concern regarding the stability of interwafer Cu vias. Guidelines for design parameter values are estimated, e.g., interwafer via size, pitch, and BCB thickness. For 2.6-/[micro]m-thick BCB, computations indicate that via size should be larger than 3 [micro]m at a pitch of 10 [micro]m to avoid plastic yield of Cu vias. Index Terms--Benzocyclobutene (BCB), Cu, interwafer vias, low-k dielectronics, thermo-mechanical stresses, three-dimensional (3-D) ICs.

In integrated power modules, mechanical properties of interfaces between deposited copper traces and substrates are important for reliable operation. This paper investigates the values of thermomechanical stresses by IDEAS simulation and describes an experimental method to calculate intrinsic residual stresses using the Stoney equation based on the bending curvature of the sample. Index Terms--Intrinsic residual stress, planar metallization, thermomechanical stress.