Reduction In Relative Density Research Articles

Effects of CNTs content on the microstructure and mechanical properties of spark plasma sintered TiB2-SiC ceramics

Monolithic TiB2 ceramics and TiB2−20vol%SiC-x vol%CNTs (x=0, 5, 10, 15, 20, 25 and 30) composites were prepared by spark plasma sintering. The influence of CNTs content and sintering temperature on sintering behavior, microstructure and mechanical properties were investigated. It was indicated that the fine grains, increased densification and homogenous dispersion of CNTs were the main dominate factors for the improved mechanical properties. The highest flexural strength (925±45MPa) and fracture toughness (10.4±0.3MPam1/2) were achieved in composite with 15vol% CNTs sintered at 1750°C. The toughness mechanism was ascribed to be crack deflection, crack bridging, CNTs debonding and pull-out. However, porous rope-like structure of agglomerated CNTs was observed by more than 20vol% CNTs addition, resulting in the reduction of relative density and mechanical properties.

Bulk Density Reduction of Injection Molded Thermoplastic Foams via a Mold Design Approach

This study investigates the inter-relationships amongst processing parameters and mold design and their effects on relative density of injection molded foams. The limitation in lowering the overall bulk density of polymeric foams is one of the main drawbacks in injection foaming process. A sheet mold with a rectangular cavity was designed and manufactured which, includes an overflow channel connected with the main cavity via a secondary gate, the size of which was varied in this research. The effects of three parameters including chemical blowing agent weight percentage, gate width, and part thickness on reduction of relative density were investigated. Full factorial test experiments were applied in this research work. The results were used to determine the optimum conditions in terms of low foam bulk density and high cell density. The results showed that enhanced cell structure can be achieved at a larger part thickness and adjusting the secondary gate to an optimum thickness. The conclusions revealed that part thickness and secondary gate width were the most influential factors on reduction of relative density and part weight.

On the response of fluidized piles from laboratory model tests in granular soils

Design guidelines of foundation anchors and piles embedded in fluidized sand comprises understanding of installation processes, defining constitutive parameters and establishing analysis techniques. These fundamental aspects have been investigated by a series of laboratory model tests designed to evaluate the mechanism taking place during pile installation through the influence of downwardly-directed vertical water jets in the geometry of fluidized cavities in saturated sands. Measurements indicate fluidization geometry to be controlled by combined effects of jet velocity and the ratio of particle and jet diameters which can be conveniently expressed by the Froude number of particles. Characteristics of the fluidized zone geometry prior and after fluidization indicate considerable reduction of relative density of fluidized samples. Limit equilibrium analysis using geotechnical parameters approaching critical state provided indicative horizontal stress levels to estimate the uplift skin friction of model steel piles.

Mammographic Density Reduction Is a Prognostic Marker of Response to Adjuvant Tamoxifen Therapy in Postmenopausal Patients With Breast Cancer

Tamoxifen treatment is associated with a reduction in mammographic density and an improved survival. However, the extent to which change in mammographic density during adjuvant tamoxifen therapy can be used to measure response to treatment is unknown. Overall, 974 postmenopausal patients with breast cancer who had both a baseline and a follow-up mammogram were eligible for analysis. On the basis of treatment information abstracted from medical records, 474 patients received tamoxifen treatment and 500 did not. Mammographic density was measured by using an automated thresholding method and expressed as absolute dense area. Change in mammographic density was calculated as percentage change from baseline. Survival analysis was performed by using delayed-entry Cox proportional hazards regression models, with death as a result of breast cancer as the end point. Analyses were adjusted for a range of patient and tumor characteristics. During a 15-year follow-up, 121 patients (12.4%) died from breast cancer. Women treated with tamoxifen who experienced a relative density reduction of more than 20% between baseline and first follow-up mammogram had a reduced risk of death as a result of breast cancer of 50% (hazard ratio, 0.50; 95% CI, 0.27 to 0.93) compared with women with stable mammographic density. In the no-tamoxifen group, there was no statistically significant association between mammographic density change and survival. The survival advantage was not observed when absolute dense areas at baseline or follow-up were evaluated separately. A decrease in mammographic density after breast cancer diagnosis appears to serve as a prognostic marker for improved long-term survival in patients receiving adjuvant tamoxifen, and these data should be externally validated.

Tribological properties of Al6061–Al 2O 3 nanocomposite prepared by milling and hot pressing

Tribological properties of bulk Al6061–Al 2O 3 nanocomposite prepared by mechanical milling and hot pressing were investigated. Al6061 chips were milled for 30 h to achieve a homogenous nanostructured powder. A 3 vol.% Al 2O 3 nanoparticles (∼30 nm) were added to the Al6061 after 15 and 30 h from the beginning of milling. The milling times with Al 2O 3 in these two samples were then 15 h and 30 min, respectively. Additionally, 3 vol.% Al 2O 3 (1 μm and 60 μm) was added to the Al6061 after 15 h of milling; where, the micron size Al 2O 3 in these two samples, was milled 15 h with the matrix. Hot pressing of milled samples was executed at 400 °C under 128 MPa pressure in a uniaxial die. The hot pressed samples were characterized by micro-hardness test, bulk density measurements, pin on disc wear test, and finally scanning electron microscopy observations. Fifteen hour-milled nanocomposite with nanoscale Al 2O 3, showed improvement in wear resistance and bulk density compared with that of 30 min-milled nanocomposites due to better dispersion of Al 2O 3 nanoparticles, improved surface quality of nanocomposite particles before pressing and more grain refinement of Al matrix. Moreover, increasing the reinforcement size increased the wear rate because of reduction in relative density, hardness and inter-particle spacing.

Phase transitions and thermal properties of gadolinium trifluoride

The temperature dependence of gadolinium trifluoride density in the solid and liquid states was determined by a gamma attenuation technique. Volume changes on solid–solid and solid–liquid transitions were measured. The density and volume coefficient of thermal expansion of the liquid salt at the melting point are equal to 5609±25 kg m−3 and (16.2±0.5)×10−5 K−1, respectively. The relative density reduction on melting equals 16.7±0.15%. The polymorphic transformation from the low-temperature orthorhombic modification (a lattice of β-YF3 type) into the high-temperature hexagonal phase (LaF3 type) occurs with an increase of the density (about 2.1%). The peculiarities of the thermal expansion of the solid rare earth fluorides, undergoing phase transition β-YF3-type→LaF3-type, are discussed.

In-Situ Sensing of the Expansion of Low Density Core (LDC) Ti-6Al-4V Sandwich Structures

ABSTRACTA combination multifrequency eddy current and laser ultrasonic sensors have been used to measure the pore expansion kinetics and elastic moduli evolution during the annealing of low density core (LDC) Ti-6Al-4V sandwich structures. The LDC samples were heated to 920°C and held there for up to 12 hr. The eddy current sensor measured the sample thickness (i.e. relative density) and revealed that the samples began to expand early during heating and was nearly complete after 4 hr at 920°C. The laser ultrasonic sensor measurements indicated a concomitant decrease in the elastic moduli with the reduction in relative density. The combination of an eddy current and laser ultrasonic sensor is therefore able to measure both the density and the elastic moduli independently during the annealing stage of LDC Ti-6Al-4V sandwich structure processing providing a simple method for directly controlling the parameters most critical to aerospace applications of these new materials.

Variation of the creep limit and structure of a welded joint in pT-3V titanium alloy under cyclic loading. Report 3

The metallographic methods and microanalysis were used for investigation of the welded butt-joint specimens from PT-3V titanium alloys. The specimens were in initial state and after cyclic loading. Duration of loading was 5·104 and 1·107 cycles on a frequency of 35 Hz. The stress amplitude was 150 MPa; this value is below the endurance limit of weld material. The polished sections for investigations were cut out from a working part of specimens, which contains all zones of weld including the base metal. The plane of the polished section was disposed parallel to the surface of the weld and the axis of the polished section was located perpendicularly to the axis of the weld. The results show that migration of interstitial impurities takes place to boundaries of weld zones and regions of primary segregation of substitution elements. This process occurs under the action of cyclic loading that is followed by reduction of relative density of movable dislocations and length of dislocation segments, which are described in Communication 2. The mentioned causes lead to stabilization of weld material structure and enable an increase in the cyclic and static creep limits as is described in Communication 1. The physical processes, responsible for stabilization of dislocation structure and growth of creep stresses, are mainly completed after 5·104 cycles of loading.

Compression Moulded Ethylene Homo and Copolymer Foams I. Effect of Formulation

Various foam formulations based on polyethylene and ethylene-vinyl acetate copolymers were investigated. Interactions between crosslinking and blowing agent concentrations were systematically studied for each base polymer using a two-stage compression moulding technique to manufacture the foams and the effects on physical properties were determined. Initial studies progressively increased blowing agent concentration, whilst maintaining a fixed crosslinking agent level, resulting in density and relative density reduction as expected. However, it was observed that at any specific blowing agent concentration, foam density increased with increasing chain branching in polyethylene and with increasing vinyl acetate content in the copolymers. This phenomenon was satisfactorily explained in terms of increasing crosslinking efficiency with increasing tertiary hydrogen concentration in the base polymer by comprehensive studies on gel content, melt strength at the expansion temperature and cell size trends. Surprisingly, cell size increased with vinyl acetate content at any particular gel content suggesting absolute cell size is a function of nucleation in the first stage of the process.