Effect Of Constituent Materials Research Articles

Experimental investigation and empirical modeling for corrosion rate prediction of biodegradable zinc based composite considering the effect of constituent materials

Biodegradable zinc (Zn) has shown great potential in the area of biomedical applications. Though, the mechanical properties are decisive for the use of Zn for orthopedic and cardiovascular applications. Consequently, one needs to focus on improving the mechanical properties of Zn for its suitability in biomedical applications. Alloying of essential elements of the human body resulted in enhancement of Zn’s mechanical properties in recent years. The corrosion rate of pure Zn is ideal; however, the addition of other elements has resulted in a loss of its ideal corrosion rate. The inclusion of hydroxyapatite (HA) and iron (Fe) in Zn has also been reported in improving the mechanical properties. Hence, a need is raised for the development of a model which can predict the corrosion rate after adding HA along with Fe in Zn. In this research work, empirical based modeling is proposed to predict the corrosion rate, which incorporates the outcome of addition of Fe and HA in Zn. The Zn based materials were fabricated with the help of microwave sintering for developing the empirical model. The corrosion properties of the materials were assessed through a potentiodynamic polarization test in a simulated body fluid solution. The enhanced corrosion rate was attained with the rise in HA (wt%) and Fe (wt%) in Zn. An empirical correlation was established between the influencing controlling parameters (i.e., corrosion current, equivalent weight, and material density) of corrosion rate. Confirmation experiments were conducted to validate the developed model, and the highest error of 6.12% was obtained between the experimental and predicted values exhibiting the efficaciousness of the proposed model.

Global buckling and multiscale responses of fiber-reinforced composite cylindrical shells with trapezoidal corrugated cores

In order to comprehensively understand the effect of composite materials on the structural response, a novel multiscale numerical model is presented in this work to study the global buckling and localized responses of composite cylindrical shells with trapezoidal corrugated cores. Treated as hierarchical structures, the investigation of composite shells includes carbon fiber-reinforced composites at micro-scale, fiber–matrix laminates at meso-scale, as well as corrugated shells at macro-scale. The well-established locally-exact homogenization theory is firstly introduced to generate the microstructural effective coefficients, which are then transferred to the lamination theory. Finally, a simplified structural homogeneous representative volume element (RVE) is established with equivalent properties to a part of cylindrical structures with inner and outer skins embedded with corrugated cores, significantly facilitating the finite element (FE) simulations. The simplified structure is validated against the 3D full-scale analysis with good agreement for critical loads of different buckling modes. The global buckling performance of corrugated cylinders is then demonstrated by considering the effect of constituent materials, fiber volume fraction and geometric parameters. More importantly, benefited from a top-down procedure, the localized stress distributions are recovered using the three-stage multiscale model, to predict the possible crack initiations starting within the microstructures.

Effects of Constituent Materials on Heat Generation in Individual EDLC Electrodes

This study aims to investigate the effect of electrode composition on heat generation in electric double layer capacitor (EDLC) electrodes under galvanostatic cycling. EDLCs consist of two identical electrodes usually made of a mixture of (i) carbon-based material, (ii) binder, and (iii) other conductive additives. These constituents were found to influence the capacitance and internal resistance of the device and the heat generation rate in the positive and negative electrodes. Indeed, the heat generation rate was measured using an isothermal calorimeter in both electrodes of five EDLC devices with different electrode compositions but the same electrolyte consisting of 1 M LiPF6 in EC:DMC. The reversible heat generation rates at the positive and negative electrodes were nearly identical in absence of CMC. However, in devices containing CMC, the reversible heat generation rate in the positive electrode was significantly larger than that in the negative electrode. Such asymmetric heating was attributed to asymmetry in the charging mechanism due to the overscreening effect caused by interactions between the anionic functional groups of CMC and the cations at the negative electrode.

Study on Stability of Functionally Graded Cylindrical Shells Subjected to Hydrostatic Pressure

The stability of submerged functionally graded (FG) cylindrical shell under hydrostatic pressure is examined in this paper. Based on the Flügges shell theory, the coupled frequency of submerged FG cylindrical shell is obtained, using wave propagation method and Newton method. Then the critical pressure of FG cylindrical shells is given by applying linear fitting method. Results are compared to known solutions, where these solutions exist. The effects of constituent materials, volume fraction, boundary condition and dimensions on the critical pressures of submerged FG cylindrical shell are illustrated by examples.

Residual Strength and Failure Criterion of PP Thermoplastic Honeycomb Sandwich Subjected to Low Velocity Impact

This paper presented the effect of constituent materials on impact damage and strength reduction of sandwich structure, composed of laminated woven E-glass facesheets and polypropylene thermoplastic honeycomb core. Effect of low-velocity impact was the main interest in a variety of layered configurations. Compression after impact (CAI) has been carried out to determine the residual strength of impacted sandwich structures. Three different thicknesses of core of 20, 40 and 60mm subjected to three different levels of impact energy of 15, 30 and 45J were investigated. Impact response of the panel was recorded and analyzed in terms of peak load, indentation, energy absorbed and time. A profile analysis using optical 3D surfaces profiler was carried out to attain the indentation depth and damage area of the samples. The tested samples were then sectioned into halves to capture the failure mode or damaged sequence of the polypropylene thermoplastic honeycomb core. The dominant failure modes of the core indicated that polypropylene thermoplastic honeycomb core is a high strength material which can absorb higher impact energy and retain a higher degree of structural integrity.

Additivity effects in the rheology of fresh concrete containing water-reducing admixtures

Freshly mixed concrete must be capable of being transported and placed, flowing into moulds and around reinforcement, compacted and finished, all without segregating. Modern concrete admixtures can reduce the water content needed for such performance by up to 30% with a resulting considerable increase in strength. It is well established that fresh concrete conforms to the Bingham model and since 1970s considerable data on the effects of constituent materials and their relative proportions on the yield stress and plastic viscosity has been collected. In mix selection it has been assumed, but never explicitly demonstrated, that these effects are additive. This paper reports a series of experimental water-reduced concretes, where the addition of superplasticiser reduces the yield stress, which is offset by reduced water content to return the yield stress to the original value. The reduced water content increases the plastic viscosity, leading to mixes which are sticky and difficult to handle. The results provide evidence in support of the concept of the additivity of constituent effects in the rheology of fresh concrete, which can be visualised as the vector sum of the effects when plotted on a graph of yield stress against plastic viscosity.

On the application of liquid‐crystal thermography for the nondestructive detection of delamination in composite structures

AbstractTo prevent the catastrophic failure of composite structures, several nondestructive testing methods have been developed. In this study, a new technique to evaluate these structures by using thermochromic liquid crystal (TLC) thermography is presented. Temperature gradients produced by sensitive liquid‐crystals are used to detect delamination in composite specimens. The effects of constituent materials and delamination size/location are investigated. The results from TLC thermography are compared to those from infrared thermography. Finally, advantages/disadvantages of the new method are discussed. On the basis of the results from this study, it could be concluded that the TLC thermography can be used as an inexpensive nondestructive testing method in inspection of composite structures. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Strength reduction behavior of honeycomb sandwich structure subjected to low-velocity impact

The paper deals with the effect of constituent materials on impact damage and strength reduction of a sandwich structure, composed of laminated facesheets and Nomex ® honeycomb core. Low-velocity impact tests were performed and damage was inspected by scanning acoustic microscopy. In addition, static tests were conducted under flexural loading. The damage behavior is characterized through the energy absorbed during impact. The strength reduction is evaluated via a residual strength prediction model. A statistical model is developed to identify the variation of residual strength of the impacted structure.

The Growth of SiC Crystals from CoSi Molten Alloy Fluxes

The growth of SiC single crystals from SiC saturated Co-Si molten alloy fluxes is reported. Experiments were performed by two routes: liquid phase sintering of CoSi/SiC and Si/Co/SiC powder compacts and melt infiltration of CoSi alloy into porous SiC powder preforms. Results showed that euhedral SiC crystals, many of which appeared as polygonal or plate shaped single crystals, grew from the SiC saturated CoSi molten alloy. The largest SiC crystals exceed half millimetre in size, after 25h of isothermal dwelling at 1700°C in the melt infiltration process. The nature of the growth mechanism, the crystal defects and the effects of constituent materials, temperature and time on the abnormal grain growth of SiC single crystals are further discussed.

Effects of Constituent Materials and Quantities on Water Demand and Compressive Strength of Controlled Low-Strength Material

Controlled low-strength material (CLSM) is a self-compacting, flowable, low-strength, cementitious material used primarily as backfill, void fill, and utility bedding in lieu of conventional compacted fill. Potential advantages of CLSM include decreased labor requirements, faster construction speed, and potentially lower in-place cost. When considering CLSM as a construction material, 2 of the most important properties include flowability and compressive strength. The flowability of CLSM can directly impact productivity and human resource requirements for placing the material. Lower flowability may require more resources. In addition, compressive strength values are required as an indicator for performance and long-term excavatability. Minimum strength requirements are necessary for performance criteria, and maximum strength requirements are necessary for long-term excavation. This research investigated the effects of material properties on the water demand necessary to obtain minimum flowability values and a range of compressive strength values for CLSM. Three types of aggregate, 3 types of fly ash, and 1 Type I cement were used in this study. A total of 31 mixtures were developed and tested. The use of different aggregate types and sources was found to be the most significant factor affecting water demand in this investigation. Water-cement ratio, aggregate sources, and fly ash type were influencing variables on the compressive strength of CLSM. Formulas were developed to predict the compressive strength development of CLSM for the materials used in this research program.

Effect of Constituent Materials upon Spectrographic Measurement of Seven Impurity Elements

Effect of Constituent Materials upon Spectrographic Measurement of Seven Impurity Elements