Investigation Of Thermomechanical Behavior Research Articles

Investigation of thermo-mechanical behavior, proton transfer and methanol permeation of polymer electrolyte membrane in low sulfonated state modified with thermally stable surface functionalized graphene oxide nanosheets

Sulfonated polyether ether ketone is currently under investigation to replace the expensive Nafion® as polymer electrolyte membrane. Sulfonic acid group is hydrophilic in nature and plays a key role in proton transfer in polymer electrolyte membranes. The higher the degree of sulfonation the higher proton conductivity in sPEEK based polymer exchange membrane is achieved; however, high degree of sulfonation causes severe dimensional instability due to higher water uptake which in turn affects membrane fuel retention capabilities as well as thermo-mechanical strength. Graphene oxide nanosheets were functionalized with aryl dizonium salt of p-Aminobenzene sulfonic acid for modification of sPEEK in low sulfonated state (DS = 53%) to improve its proton conductivity and suppress fuel crossover. The functionalization was carried out to compensate for the possible dilution of proton exchangeable sites by fillers. The resulting membranes were characterized in terms of morphology, thermo-mechanical behavior, methanol permeability, water uptake, and proton conductivities. The results proved that sulfonated GO not only improved thermo-mechanical behavior of the membrane but also dramatically increased proton conductivity (47 mS cm−1) than pristine sPEEK (25 mS cm−1). The composite membranes showed highly reduced methanol crossover compared with pristine sPEEK. The electrochemical selectivity increased from 9.5 × 104 Scm−3s (pristine sPEEK) to 26.9 × 104 Scm−3s.

Investigation of thermo mechanical behaviour in the scaled PHWR stepped calandria vessel during severe accident

In case of Indian Pressurized Heavy Water Reactors (PHWRs), in-calandria retention of corium is essential for mitigating core melt down accident. Benchmark calculations have shown that if corium breaches the calandria vessel and enters the calandria vault, large amount of hydrogen and other fission gases may be generated due to molten corium concrete interaction (MCCI). There is possibility of containment failure. Hence, the best option is to contain the corium inside the calandria vessel and cool it from outside by calandria vault water. PHWR calandria vessel thicknesses varies from 22mm to 32mm and have weld joints due to the steps involved. It is true that smaller calandria vessel thickness has lower temperature gradient and may promote higher heat transfer rate. However, there is an international concern about the healthiness of the thin vessel with stepped weld joints due to the thermal loading of high temperature corium melt which can lead to excessive thermal strain of vessel and weld joints and it may result in failure before the corium stabilization inside the vessel is achieved. In the present study, experiments were conducted in a scaled facility of an Indian PHWR to investigate the thermo-mechanical behaviour of simulated stepped calandria vessel with weld joints. The temperature distributions and the strain contours of vessel were recorded. Numerical analysis was carried out to validate the FEM model with the test data and also analysis was extended to predict the thermo mechanical behaviour of prototypic stepped calandria vessel.

Numerical Investigation of Thermo-Mechanical Behaviour of Ball Grid Array Solder Joint at High Temperature Excursion

The solder joints of surface mount components (SMCs) experience thermal degradation culminating in creep and plastic shear strain deformation when subjected to cyclic temperature load over time. Degradation at the joints is due to thermal stress induced by the incompatible, differential and nonlinear expansion mismatch of the different bonded materials in the assembly. The stress magnitude influences the strain behaviour. Plastic strain response of solder joint is critical at the materials interface at the lower part of the joint due to the occurrence of wider variation in the coefficient of thermal expansion of the bonded materials and this may lead to static structural failure. The life expectancy of electronic components reduces exponentially as the operating temperature increases thus making reliability a key concern for electronic systems operating at high temperatures and in harsh environments. This paper reports on the numerical investigation of thermo-mechanical response of a critical BGA joint especially the character of plastic deformation of SnPb solder used in forming the joint as well as the joint’s high temperature reliability. The analysis uses a 3-D models to predict the effect of the transient thermal load on the static structural integrity of a single BGA joint. In this study, the base diameter of solder ball (interface between the PCB, copper pad and the solder) experienced higher damage than the top diameter interconnects. The paper provides a simplified methodology to study the reliability of BGA solder joint at high temperatures excursion.

Influence of atmospheric plasma on physicochemical properties of vapor-grown graphite nanofibers

Vapor-grown graphite nanofibers (GNFs) were modified by plasma treatments using low-pressure plasmas with different gases (Ar gas only and/or Ar/O 2 gases), flow rates, pressures, and powers. Surface characterizations and morphologies of the GNFs after plasma treatment were investigated by X-ray photoelectron spectroscopy (XPS), contact angle, titration, and transmission electron microscopy (TEM) measurements. Also, the investigation of thermomechanical behavior and impact strengths of the GNFs/epoxy composites was performed by dynamic–mechanical thermal analysis (DMTA) and Izod impact testing, respectively. The plasma treatment of the fibers changed the surface morphologies by forming a layer with a thickness on the order of 1 nm, mainly consisting of oxygen functional groups such as hydroxyl, carbonyl, and carboxyl groups. After functionalization of the complete surfaces, further plasma treatment did not enhance the superficial oxygen content but slightly changed the portions of the functional groups. Also, the composites with plasma-treated GNFs showed an increase in T g and impact strength compared to the composites containing the same amount of plasma-untreated GNFs.