Thermal Mechanical Response Research Articles

Thermoelastic analysis of cracked woven GFRP laminates at cryogenic temperatures

Abstract We deal with the thermal–mechanical response of multi-layered G-11 woven glass/epoxy laminates with cracks and temperature-dependent properties under tension at liquid helium temperature (4 K). The composite material is assumed to be in generalized plane strain. Cracks are located in the fill fiber bundles and are assumed to span the width of the fill fiber bundles. Finite element model is used to study the influence of residual thermal stresses on the mechanical behavior of multi-layered woven laminates with cracks. Numerical calculations are carried out, and the Young's modulus and stress distributions near the crack tip are shown graphically.

Transient thermal-mechanical response of glass-fiber reinforced plastics at low temperatures

We consider the transient thermal-mechanical behavior of glass-fiber reinforced plastics with temperature-dependent properties at low temperatures. The layered composite is made of a layer bonded between two layers of different physical properties, and it is suddenly cooled on the surfaces. The composite material in generalized plane strain is assumed. The thermal and elastic properties as functions of temperature are compiled from the experimental data. Numerical results presented, include the transient temperature distribution and the thermal-mechanical stress.

513 き裂を有する極低温用平織 GFRP 積層板の熱弾性解析

Abstract We deal with the thermal–mechanical response of multi-layered G-11 woven glass/epoxy laminates with cracks and temperature-dependent properties under tension at liquid helium temperature (4 K). The composite material is assumed to be in generalized plane strain. Cracks are located in the fill fiber bundles and are assumed to span the width of the fill fiber bundles. Finite element model is used to study the influence of residual thermal stresses on the mechanical behavior of multi-layered woven laminates with cracks. Numerical calculations are carried out, and the Young's modulus and stress distributions near the crack tip are shown graphically.

Thermally-Induced Failures in Railroad Tapered Roller Bearings

An Association of American Railroads (AAR) class F (6 1/2 × 12) tapered-roller bearing assembly is modeled, using finite elements, to examine thermally-induced failures observed in the laboratory when the bearing is operating at relatively high speeds. It is hypothesized that this failure is caused by an unstable thermal expansion/internal bearing load feedback process. Sequentially-coupled, transient thermal and static structural models are used to obtain the thermal-mechanical transient time response as a function of speed, seal type, and lubricant starvation at the rib contact. The model assumes no external loads and zero initial preload (zero end-play). Therefore, the loads developed in the bearing are thermally-induced and self-equilibrated. Two train speeds, viz. 80 and 100 mph, are considered. Simulation results indicate that at axle rotational speeds equivalent to a train speed of 100 mph, a combination of grease starvation and heat flux from the contact seals cause high rib temperature and subsequent unstable load growth which will lead to failure. At rotational speeds equivalent to train speeds of 80 mph or for bearing assemblies that utilize special design seals, the rib temperature is relatively low and no operational instabilities were observed for the model used. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Priming enhances endotoxin-induced thermal hyperalgesia and mechanical allodynia in rats

Central inflammation is an integral component and contributor of the pathology of many debilitating diseases and has been shown to produce spontaneous pain and hyperalgesia. Recently, administration of lipopolysaccharide (LPS) into the lateral ventricle of rats was shown to elicit both thermal hyperalgesia and tactile allodynia [K. Walker, A. Dray, M. Perkins, Hyperalgesia in rats following intracerebroventricular administration of endotoxin: effect of bradykinin B1 and B2 receptor antagonist treatment, Pain 65 (1996) 211-219]. In this study, we have replicated the LPS model with some adaptations and correlated the nociceptive behaviors with an increased expression of activated macrophages in the central nervous system. We also examined the effects of priming on LPS-induced decreases in thermal nociceptive thresholds and mechanical response thresholds following either central or peripheral administration. Intracerebroventricular (i.c.v.) administration of LPS (0.2 microgram/rat) did not alter either thermal (hot plate) or mechanical (von Frey filaments) thresholds compared to baseline values in the first few hours after injection. However, priming rats by pretreating with i.c.v. LPS (0.2 microgram) 24 h prior to testing with i.c.v. LPS (0.2 microgram) produced significant mechanical allodynia and thermal hyperalgesia. The mechanical allodynia had an onset of 80 min after injection and a duration of 5 h. A similar time course was observed for thermal hyperalgesia, although its expression was less pronounced. Immunohistochemical studies indicated an increased expression of activated macrophages in the brain parenchyma of primed rats but not in unprimed rats. Intraperitoneal (i.p., 2 mg/kg) administration of LPS had no significant effect on either thermal or mechanical thresholds in the first few hours after injection; however, priming rats via i.p. (0.2 mg/kg) or i.c.v. (0.2 microgram) LPS produced a reduction in both thermal nociceptive thresholds and mechanical response thresholds in rats given a subsequent i.p. injection of LPS. This study demonstrates that priming is an effective protocol for the induction of central inflammation and increases the duration of these behaviors after i.c. v. administration.

Relationship between grain size and some surface roughness parameters of rock joints

On-going Single Heater Tests (SHTs) are conducted in the Exploratory Studies Facility (ESF) to study the thermal-mechanical responses of the rock mass. In addition to the heater hole and those used for Sandia National Laboratory's (SNL's) thermal-mechanical studies, a set of 14 boreholes were drilled in the test region to conduct a scoping test of the coupled thermal-mechanical-hydrological-chemical (TMHC) processes. For the TMHC tests, the boreholes are equipped with electrical resistivity tomography (ERT), neutron logging/temperature, hydrological, and optical multiple point borehole extensometer measurement devices. The heater hole contains a 4-kW heater, which was energized on August 26, 1996. Our results show that some movements of the water around the heater have occurred, which might be associated with a possible dry-out region near the heater, and the water appears to be more dilute than the in situ ground water, except for the concentration of Ca. This indicates that fractures are the major water pathways, and the displaced water may have reached an equilibrium with carbonate minerals on the fracture surfaces. No mechanical-hydrological coupling has been observed yet.

Thermal-mechanical-hydrological-chemical responses in the single heater test at the ESF

On-going Single Heater Tests (SHTs) are conducted in the Exploratory Studies Facility (ESF) to study the thermal-mechanical responses of the rock mass. In addition to the heater hole and those used for Sandia National Laboratory's (SNL's) thermal-mechanical studies, a set of 14 boreholes were drilled in the test region to conduct a scoping test of the coupled thermal-mechanical-hydrological-chemical (TMHC) processes. For the TMHC tests, the boreholes are equipped with electrical resistivity tomography (ERT), neutron logging/temperature, hydrological, and optical multiple point borehole extensometer measurement devices. The heater hole contains a 4-kW heater, which was energized on August 26, 1996. Our results show that some movements of the water around the heater have occurred, which might be associated with a possible dry-out region near the heater, and the water appears to be more dilute than the in situ ground water, except for the concentration of Ca. This indicates that fractures are the major water pathways, and the displaced water may have reached an equilibrium with carbonate minerals on the fracture surfaces. No mechanical-hydrological coupling has been observed yet.

Martensitic Transformations in a NiTi Fiber Reinforced 6061 Aluminum Matrix Composite

Approximately 19.5 volume percent, 50.7 at % Ni-Ti shape memory alloy fiber reinforced 6061-T6 aluminum alloy matrix composite (SMA-MMC) and homogeneous 6061-T6 control materials were produced by vacuum hot pressing. The test materials were initially subjected to a 5.8% tensile elongation at room temperature. During this process, the shape memory alloy reinforced composite materials exhibited a bimodal yield. The initial yield was due to plastic flow in the aluminum matrix, the subsequent yield was due to the initiation of a stress induced austenite to martensite (SIM) transformation in the shape memory alloy fibers. The SMA-MMC specimens exhibited unusual positive curvature hardening during the final stages of the 25°C tensile loading resulting from the saturation of the SIM transformation. During the subsequent 25 °C to 75 °C unconstrained heating process, the SMA-MMC exhibited a nonlinear thermal contraction resulting from the martensite to austenite shape memory transformation of the NiTi reinforcement. At the conclusion of the unconstrained heating process the temperature was held constant at 75°C as the loading grips were reapplied and the test materials were tensile loaded to failure. The elevated temperature flow strength of the SMA-MMC was significantly higher than the final SMA-MMC room temperature flow strength; this increase was due to the imposition of a large longitudinal compressive stress in the composite matrix by the NiTi fiber shape memory response, and due to the increase in NiTi fiber transformation stress with increased temperature. The elevated temperature ultimate strength and final failure strain of the SMA-MMC materials were both significantly higher than that of the 6061-T6 control materials. The experimental results are analyzed by a nonlinear, one-dimensional composite constitutive model. The model provides a compact quantitative description of the SMA-MMC thermal mechanical response as a function of temperature and applied stress, and correctly expresses important experimental features.

Mechanical behavior of woven composites at low temperatures

Abstract This paper deals with the thermal mechanical response of nonmetalic woven composites with temperature-dependent properties. The composite material in generalized plane strain is assumed. First, a finite element method is used to study the influence of crack formation, residual thermal stresses and weave curvature on the mechanical performance of G-10CR glass-epoxy laminates at low temperatures. Next, we examine the stress state at the free edge of the woven composites. Last of all, we calculate the mechanical properties of the woven composites. Numerical results on the distribution of stresses and the mechanical properties at different temperatures and warp angles are obtained and presented in a graph form.

極低温におけるき裂を有する織物複合材料の力学的特性に関する有限要素解析

This paper deals with the thermal mechanical response of cracked nonmetallic woven composites with temperature-dependent properties. The composite material in generalized plane strain is assumed. Finite element method is used to study the influence of crack formation, residual thermal stresses and weave curvature on the mechanical performance of G-10CR glass/epoxy laminates at low temperatures. Numerical results on the influence of the crack on the mechanical properties and the distribution of stresses at different temperatures and warp angles are obtained and presented in a graphic form.

Thermal mechanical response of cracked glassfiber reinforced plastics at low temperatures.

Abstract-Large quantities of nonmetallic composites such as G10-CR and G11-CR are currently under study as possible materials for magneteic fusion energy structures at low temperatures. Here we study the thermal mechanical response of cracked G10-CR glass/epoxy laminates. The composite material in generalized plane strain is assumed. Fourier transforms are used to reduce the problem to the solution of a pair of dual integral equations. The solution of the dual integral equations is expressed in terms of a Fredholm integral equation of the second kind. Numerical results on the thermal stress intensity factor and the influence of the crack on the mechanical properties at different temperatures are obtained and presented in graph form.

Structural response of materials due to in-depth heating

The effect of uniform through-thickness energy deposition on the thermal-mechanical response of several structural materials is evaluated. Expressions used for determining temperature distributions under moderate deposition rates are presented. Temperature histories of aluminum, titanium, and graphite-epoxy panels subject to electron beam irradiation are compared with analytical results to assess the validity of the methods used. Dynamic material response under extreme deposition rates are developed for instantaneous and finite pulse deposition. Expressions for determining the regime of dominant thermal or dynamic response are given as a function of total energy and energy deposition rate. 11 references.

Three Dimensional, Thermal Stress Analysis of a Welded Plate by the FEM

A general numerical model for simulating three-dimensional thermal stress analysis has been developed which uses the Finite Element Method (FEM). The analysis can be uncoupled to solve either the heat transfer problem or the stress problem independently and it can accommodate nonlinear material behaviour, initial states of stress and strain, and moving boundary conditions. A unique feature of the model is that it properly accounts for the latent heat effect during phase changes. Applying the moving heat flux boundary condition to simulate arc welding, the model has been used to predict the transient thermal mechanical response of a welded plate.

A Finite-Element Solution of Thermal Distortion with Applications to Thrust Bearings

A finite-element code to account for thermal expansion in a solid was developed for the Independent Research and Independent Exploratory Development project "Tribology of Sliding Surface Bearings." The program is based on a two-dimensional model using a second or higher-order interpolation function in the element space that will allow a diverse temperature field, such as a steep nonlinear temperature gradient, to be prescribed in a solid body. The computer code has a definite advantage over certain finite-element systems that are commercially available. Many accept only a constant, or averaged, temperature input into their element space. With the new capabilities, complex thermal mechanical responses under severe temperature gradients can be readily analyzed. For instance, the hot spot in a ship's landing deck due to the concentrated heat load, such as those generated by high-temperature jet exhaust, can be more realistically represented by the elements of current development. The element mesh size and the input data set are more manageable.

Design, Fabrication and Testing of a Rock Instrumentation System for Monitoring the Thermal-Mechanical Response of Basalt

In situ testing was conducted to monitor the thermal-mechanical response of basalt subjected to heat loads simulating those expected in an actual nuclear waste repository. This paper describes the rock instrumentation system, the reliability testing program and the instrument modifications which were adopted as a result of that testing. Over 20 different performance tests were undertaken to provide calibration factors and to verify the reliability of the instruments under water-saturated conditions and temperatures as high as 200/degree/C. 9 refs.

Structural and mechanical properties of polybutadiene‐containing polyurethanes

AbstractA series of segmented polyurethanes based on hydroxylterminated polybutadienes (HTPBD) and their hydrogenated derivatives (HYPBD) has been synthesized. Thermal, mechanical, and spectroscopic studies were carried out over a wide temperature range to elucidate the structure‐property relationships existing in these polymers. Both thermal and dynamic mechanical response showed a soft segment Tg at −74°C for the unsaturated polyurethanes and at −69°C for the hydrogenated samples. In addition, two hard segment transitions are observed by differential scanning calorimetry (DSC) at 40 and 75°C and a softening region by thermal mechanical analysis (TMA) at 190°C. The low Tg, very close to that of the free HTPBD and HYPBD and independent of hard segment content, indicated that these polymers were well phase separated. Results of infrared analysis revealed that at room temperature, 90‐95 percent of the urethane N‐H groups formed hydrogen bonds. Since hydrogen bonding resides only within the hard segment domain in these butadiene‐containing polyurethanes the extent of H‐bonding served as additional evidence for nearly complete phase segregation. From dynamic mechanical studies, the plateau modulus above the soft segment Tg and stress‐strain behavior depended upon the concentration of hard segments. A slight increase in the modulus, a moderate increase in stress (σb), and decrease in elongation accompanied a higher hard segment content. The thermal and mechanical response of these polyurethanes appears to be consistent with behavior observed for other phase segregated systems. Variations in behavior resulting from hydrogenation of the precursor prepolymer are discussed.

First Wall Thermal-Mechanical Analyses of the Reference Theta-Pinch Reactor

The thermal-mechanical response of the Reference Theta-Pinch Reactor (RTPR) first wall was analyzed. The first wall problems anticipated for a pulsed, high-..beta.. fusion power plant can be ameliorated by either alterations in the physics operating point, materials reengineering, or blanket/first wall reconfiguration. Within the latter ''configuration'' scenario, a two-fold approach has been adopted for the thermal-mechanical portion of the RTPR first wall technology assessment. First, a number of new first wall configurations (bonded or unbonded laminated composites, all-ceramic structures, protective and/or sacrificial ''bumpers'') were considered. Second, a more quantitative failure criterion, based on the developing theories of fracture mechanics, was identified. For each first wall configuration, transient heat transfer and thermoelastic stress calculations have been made. Two-dimensional finite element structural analyses have been made for a variety of mechanical boundary conditions. Only the Al/sub 2/O/sub 3//Nb - 1 Zr system has been considered. The results of this study indicated a wide range of design solutions to the pulsed thermal stress problem anticipated for the RTPR.

Thermal-mechanical response of nearly opaque materials exposed to continuous radiation

Thermal stress distribution and temperature profiles in nearly opaque spherical shell under radiant and convective heating flux