Influence Of End Conditions Research Articles

Mechanical and damping property evaluation of jute fiber reinforced composite periodic core sandwich panels

ABSTRACT The present article investigates the dynamic characteristics of jute fiber-reinforced sandwich composite panels with periodic cores. The sandwich panel contains the jute fibers-reinforced polymer (JFRP) composites as face layers and the silicone rubber as the core layer. The tensile and flexural properties of JFRP composite material were examined using ASTM D3039 and ASTM D7264 standards. The finite element model was developed to obtain the dynamic properties of the composite sandwich panel with conventional and periodic cores. Furthermore, the influence of end condition, core to face layer thickness ratio, and face layer to core thickness ratio on the dynamic properties of the sandwich panels are presented. The numerical results indicate that the periodic core composite sandwich panel greatly influences the structural stiffness compared with a conventional composite sandwich panel.

Structural Reliability Evaluation of Thermoelectric Generator Modules: Influence of End Conditions, Leg Geometry, Metallization, and Processing Temperatures

Structural reliability of thermoelectric generators (TEGs) in medium to high temperature applications still remains a challenge. Currently there are no established standards for evaluating the thermomechanical reliability of TEGs during new material and module development phases in the industry. In this work we implemented a procedure for evaluating the reliability of brittle TE materials based on the common practice in the ceramics industry. The probabilistic thermomechanical reliability of TEG couples and modules is evaluated using Weibull analysis. Finite element simulations were carried out to study the influence of TEG couple parameters such as leg geometry, dimensions, spacing, metallization thickness, and processing conditions on the stresses, and the structural reliability evaluations were conducted based on the TE material stresses. Results showed that the boundary conditions and processing temperatures have significant influence on the TE material and metallization stresses and overall device reliability. The external compressive load significantly enhanced structural reliability. Results also showed that among geometrical parameters the leg length has a dominating influence on the overall stresses compared to the leg cross-sectional shapes. The cross-section geometry of legs showed considerable effect at shorter lengths, and the influence diminished with increased lengths. The proposed approach for evaluating the structural reliability could be integrated with performance optimization techniques for developing optimal and reliable TEG devices.

Influence of end-conditions during tube hydroforming of aluminum extrusions

Tube hydroforming experiments were conducted to develop the forming limit diagram of AA6082-T4 by utilizing three types of end-conditions: (i) “free-end”, (ii) “pinched-end” or “fixed-end” and (iii) “forced-end”. It was found that “free-end” hydroforming gives the lowest forming limits followed by “pinched-end” and “forced-end” hydroforming. It was noticed that the tube failure occurs within 5° to the extrusion weld in the “free-end” experiments, within 7° in the “pinched-end” condition and extended up to 10° in the “forced-end” hydroforming experiments. Finite element simulations were carried out to capture the effects of the weld geometry, weld mechanical properties and the end-conditions of the extruded tube on the maximum induced stress and location of the maximum von Mises stress. It was found that the anisotropy of the weld material and the end-condition used during hydroforming experiments have the largest influence on the failure location with respect to the weld center.

円管の衝撃軸圧縮塑性座屈実験

Progressive plastic buckling appears in the axial symmetric behavior of circular tubes subjected to static loads or low velocity impacts, when the inertia effect is negligible. For high velocity impacts in which inertia cannot be neglected, the studies by Tanaka and Kurokawa revealed the appearance of the same modes as those in static tests. However, a series of impact tests on tubes by Florence et al. recorded the phenomenon of dynamic plastic buckling in which the deformation consists of many waves superposed on a uniform plastic deformation. This phenomenon was found for moderately thick circular tubes subjected to high velocity axial impacts. Ren et al. observed that dynamic plastic buckling developed on thin circular tubes. Thus, the plastic buckling behavior for high velocity impact tests on circular tubes consist of both progressive plastic buckling and dynamic plastic buckling, but the detailed behavior is not clear yet.The purpose of this study is to clarify the characteristics for the transition process from progressive plastic buckling to dynamic plastic buckling. In particular, the following features are examined:(1) The comparison and consideration of various experimental methods used in the previous impact test results.(2) The influence of end condition on the static buckling behavior of circular tubes.(3) The consideration of some impact test results.

The Influence of End Conditions on Minimum Film Boiling From a Cylinder

Upon preparing for an experiment in which liquid-solid contacts were to be measured near the minimum film boiling point in flow boiling, it became clear the thermal condition of the heater ends could exercise undue restrictions on the achievable minimum heat flux and wall superheat. For the experiment in question, the heater was to be heated electrically while suspended horizontally across a flow of Freon-11 (R-11). The heater surface was mounted flush with the inside wall of the test section, bringing into play the interaction with the wall as well as potential axial heat loss from the heater during film boiling. Thus the authors set out to investigate the influence of end conditions using a simpler pool boiling apparatus very similar to the flow boiling apparatus. This paper details how modifications of the end conditions for an electrically heated cylinder influence the minimum film boiling point that is achievable in R-11. The modifications consisted of providing guard heating of the ends along with properly designed heater supports so that the heater temperature does not fall off precipitously near the ends. If the end temperature is not maintained high enough, transition boiling begins at the ends while the majority of themore » heater is immersed in a vapor film. Once the film begins to collapse, it becomes unstable and nucleate boiling ensues.« less

Effects of size and end conditions of a heated surface upon minimum film boiling.

An experiment of boiling for saturated water and saturated R113 was made at atmospheric pressure on a horizontal cylinder and a horizontal circular plate. The diameter of the cylinder or the plate was varied widely to study size effects. Several end conditions were tested to examine end effects. The influence of end conditions was found to be very strong on the minimum heat flux of the cylinder. By setting the temperature of the end of cylinder sufficiently high, the end effect was removed and minimum qmin was obtained. The value of minimum qmin agrees well with the prediction of Lienhard and Wong when the diameter of cylinder is small, but it deviates and tends toward Berenson's prediction as the diameter increases. In the experiment on a flat plate, two transition points were observed. The critical size of the plate, above which no end effects as well as no size effects can be detected, is found to be 5 lcr or 3λd for film boiling or for minimum film boiling.

Effect of End Conditions on the Burst Strength of Finite Cylinders

Solutions are presented for the bursting strength of thin-walled cylinders of finite length with various end restraints, including (a) two rigid end plates, (b) two hemispherical caps, and (c) one rigid end plate and one hemispherical cap. The deformation theory of plasticity is used, together with the Mises yield criterion, for materials obeying a linear strain-hardening law. Comparisons of the results are made to determine the influence of end restraints on burst pressure with numerical results presented for cylinder lengths from 0 (sphere) to ∞, and for a range of hardening constants. The results show that the effect of shortness is small (less than 8 percent), and the influence of end conditions negligible, in the range l > 3. For shorter cylinders, the finite length of the shell serves to increase burst pressures, to values nearly double those for the infinite cylinder, as l → 0. Also, the effect of end restraints becomes very pronounced, the cylinder with the two rigid end plates being the strongest, and that with two hemispherical caps the weakest; all other types of end closures are assumed to have a strengthening effect intermediate to these two cases.