Samples Of Different Densities Research Articles

The Influence of Technological Parameters on the Structure and Properties of the Selective Laser Melting Al–Cu–Mg–Si Alloy

Abstract—Monolithic and bulk-structured samples of different densities were produced by means of selective laser melting on the 3D-metal printer Realizer SLM 100. An evaluation of their quality and structure characterization were carried out. Correlation of parameters of synthesis—intertrack distance and layer thickness at 200 W laser power, and structural characteristics were determined. According to the experimental results, optimal parameters of the synthesis were found for obtaining samples from AK6 alloy with dispersed structure and high mechanical properties. Correlation of the fine structure paramerers of the volume-structured samples with cubic geometry and synthesis parameters were established, types of defects that affect their mechanical properties were determined.

Statistical damage constitutive model for the two-component foaming polymer grouting material

Abstract Two-component foaming polymer (TFPU) grouting material is increasingly used in civil engineering. Its compressive strength is key to achieving the desired enhancing effect. The constitutive model of TFPU grouting material is a theoretical basis to evaluate the strength performance, which, however, is not fully understood. Here the uniaxial compression experiment of TFPU samples of different densities (0.11–0.53 g·cm−3) was conducted. Based on the stress–strain curves, the damage evolution equation of each sample was obtained by function fitting, followed by the establishment of statistical damage constitutive model. The model was simplified to a universal function with density as the argument. Results show that the stress–strain curves contain the initial compression stage, linear elastic stage, yield stage, yield plateau stage, and strain hardening stage regardless of the varied density. The variation laws of the damage with strain conform to the form of first-order decay exponential function. The theoretical stress–strain curves are in good agreement with the experimental ones, indicating that the statistical damage constitutive model can well reflect the mechanical behavior of TFPU grouting material. With this constitutive model, the mechanical properties of TFPU grouting material can be obtained according to the density alone, which is more convenient for practical engineering applications.

Dependence of the mechanical properties of rigid PU foam on density

Density is an important parameter that influences the properties and performances of rigid polyurethane foam. In this study, a systematic engineering approach is presented for determining the effect of density on mechanical properties of rigid/crushable PU foam for design applications. To this end, several mechanical performance parameters, that is, mean load and strength, secant modulus, energy absorption efficiency and densification strain are at first identified for the PU foam. Foam samples of different densities are obtained by varying the amount of liquid polyol–isocyanate of a desired mixing ratio in a constant-volume cubical mould and letting the blow and gelation reactions progress to completion. By conducting compression tests on cubic specimens of foam obtained, it is shown that various mechanical parameters of interest increase monotonically with respect to density. An SEM-based study on the effect of density on foam microstructure has also been carried out.

Sugarcane bagasse waste fibers as novel thermal insulation and sound-absorbing materials for application in sustainable buildings

Global warming and noise pollution have emerged as the most serious environmental problems ever to confront humanity. In recent years, the use of natural fibers as thermal insulation and sound absorption construction materials has received much attention. Sugarcane bagasse waste (SBW) is an agro-industrial by-product, abundantly produced in sugar processing plants. Endowed with intrinsic surface roughness, SBW fibers are expected to exhibit high thermal and acoustic performance. To this end, SBW as an eco-friendly material was used to fabricate fibrous samples of different densities and thicknesses. The thermal insulation and sound absorption performance of the specimens were investigated using the guarded hot plate and impedance tube techniques, respectively. Additionally, the surface morphology and tensile properties of the SBW fibers were investigated using the FE-SEM and universal tensile tester. The thermal conductivity values of the specimens were found to range between 0.034 and 0.042 W/mK. The sound absorption average (SAA) and noise reduction coefficient (NRC) of the prepared samples were between 0.26-0.64 and 0.27–0.62, respectively. The results pointed to the good performance of the SBW fibers in the low- and mid-frequency ranges. The acoustic characteristics of the specimens were also studied by the Johnson-Champoux-Allard and statistical models and good agreement with experimental data was noticed. It was concluded that SBW as an innovative sustainable construction material provides competitive performance in terms of thermal and acoustical characteristics compared with its natural and nonrenewable counterparts.

On studying the mechanisms and assessing the safety of Nd:YAG laser irradiation of the posterior lens capsule (experimental and clinical study)

To study the mechanisms of laser destruction in exposing the posterior lens capsule (PLC) tissue to Nd:YAG laser irradiation, and to evaluate its side effects on the cornea. The experiment involved 6 autopsy samples of human posterior lens capsule with different optical and mechanical properties, which were exposed to laser irradiation. We used the Nd:YAG ophthalmic laser LPULSA SYL-9000 Premio manufactured by «LightMed» (Taiwan/USA) and an experimental Nd:YAG laser system (1.064 μm). The following parameters were compared: the power of the incident radiation and radiation transmitted through the PLC, the mechanical stresses in the PLC tissue, the kinetic energy of the laser ablation products, and the pressure of gas bubbles during laser exposure in capsule samples of different densities. In the clinical part of the work, the negative effects of Nd:YAG laser on the cornea at different PLC densities were assessed using the endothelial microscope SP 3000P («Topcon», Japan). The experiment showed that in hard samples of PLC there are star-shaped point perforations with a diameter of 50±20 μm with partial rarefaction around the point defects. Damage to soft PLC samples in the form of large complete perforations was up to 200 µm in size. The temperature of laser irradiation necessary to achieve breakdown in soft PLC samples was 90 °C, in hard samples - 120 °C. The results of the experiment indicate that the final outcome - destruction of the PLC tissue - is safer to achieve not by increasing the energy, but by increasing the number of laser pulses. Clinical study results confirm a significant effect of the density of PLC on the values of laser energy and on the state of the cornea after laser intervention. The experimental data on the mechanisms of laser destruction of the lens capsule should contribute to the development of new and improvement of already known technologies aimed at reducing the risks associated with laser surgeries.

A Study of Preparing Samples of Hydroxyapatite with Different Densities Using Charcoal Powder

The powder of hydroxyapatite with the chemical formula Ca10 (PO4) 6 (OH) 2 was prepared locally from cow bones in the hexagonal crystal phase, and this was confirmed through the X-ray diffraction system. The proportions that formed the prepared hydroxyapatite were confirmed through the X-ray fluorescence system and found the ratio of calcium oxide to phosphorous oxide is 1.718. The hexagonal phase of the prepared hydroxyapatite was also stabilized ( fixed ) for the samples before and after the heat treatment. Some physical and mechanical properties were also conducted for the prepared samples. It was found that it is possible to prepare samples of different densities by adding different proportions of carbon (charcoal) percentage to the prepared hydroxyapatite.

Thermal transport in dynamically disordered phases of molecular crystals: A thermo activation mechanism

Isochoric thermal conductivity of crystalline 1,1-difluoroethane (F-152a freon) is measured on samples of different densities in the dynamically orientationally disordered (DOD) phase. The thermal conductivity increased with temperature, similar to how it occurs in amorphous and glass-like substances above the plateau area. It is found that this behavior can be described by a thermo-activation mechanism with constant activation energy and density-dependent pre-exponential factor. Bridgman coefficient g = − (∂lnκ/∂lnV)T is 6.0 ± 0.5. It is shown that the thermal conductivity of a number of other molecular crystals with the dynamic orientational disorder can be described in a similar way. Possible reasons for the thermal activation behavior of thermal conductivity are discussed.

A density-based threshold model for evaluating the separation of particles in heterogeneous mixtures with curvilinear microfluidic channels

Particle separation techniques play an important role in biomedical research. Inertial focusing based microfluidics using nonlinear channels is one of the promising label-free technologies for biological applications. The particle separation is achieved as a result of the combination of inertial lift force (FL) and Dean drag force (FD). Although the mathematical expressions of FL and FD have been well derived in prior studies, they are still complicated, which limits their popularity in practice. Recent studies modified these expressions through experiments and proposed a threshold model, which assumes that only particles larger than the threshold will be well focused. Although this threshold model has been used in recent studies, two varying versions of the threshold model (TM1 and TM2) prevents standardisation in practice. In addition, both models were developed with regular low-density particles and may not be applicable to samples with higher density or samples with irregular shapes. Here, we evaluated the threshold models with samples of different densities. Based on these evaluations, we derived a modified model (TM4), which additionally considers the factor of particle density to improve the accuracy of existing models. Our results demonstrated that TM4 could more reliably predict the sorting efficiency of samples within a wider density range.

Compressive Properties of A356 Closed-Cell Aluminum Foamed with a CaCO3 Foaming Agent Without Stabilizer Particles

The A356 aluminum alloy foams were fabricated by the melt foaming method using a CaCO3 foaming agent without any stabilizer particle. The samples of different densities ranging from 0.32 to 0.46 g/cm3 (relative densities of 0.12–0.17, respectively) and cell sizes ranging from 1.5 to 3.1 mm were formed. The effect of foaming conditions such as CaCO3 amount, mixing and holding time on compressive strength and energy absorption behavior were investigated. Results show that the compressive properties of the aluminum foam are characterized by three deformation stages: linear elastic stage, plastic collapse stage and densification stage. Also, the compressive stress and energy absorption capacity increase as the relative density increases. But elastic modulus of the foamed aluminum with 3 wt% CaCO3 (relative density = 14%) is higher than others because its cell size distribution is more homogeneous than others. The compressive strength of aluminum foams without any stabilizer particles is comparable to the other researches for aluminum foams with stabilizer particles at the same density.

A model for French-press experiments of dry snow compaction

Abstract. Snow densification stores water in alpine regions and transforms snow into ice on the surface of glaciers. Despite its importance in determining snow-water equivalent and glacier-induced sea level rise, we still lack a complete understanding of the physical mechanisms underlying snow compaction. In essence, compaction is a rheological process, where the rheology evolves with depth due to variation in temperature, pressure, humidity, and meltwater. The rheology of snow compaction can be determined in a few ways, for example, through empirical investigations (e.g., Herron and Langway, 1980), by microstructural considerations (e.g., Alley, 1987), or by measuring the rheology directly, which is the approach we take here. Using a French-press or cafetière-à-piston compression stage, Wang and Baker (2013) compressed numerous snow samples of different densities. Here we derive a mixture theory for compaction and airflow through the porous snow to compare against these experimental data. We find that a plastic compaction law explains experimental results. Taking standard forms for the permeability and effective pressure as functions of the porosity, we show that this compaction mode persists for a range of densities and overburden loads. These findings suggest that measuring compaction in the lab is a promising direction for determining the rheology of snow through its many stages of densification.

Effects of Different Treatments on Surface Activity of Rice Straw Particleboard

The surface activity of rice straw particleboard (RSP), which has a significant effect on the finishing and bonding performance, is reduced by wax coating and free radicals on the straw fiber. The RSP surface was treated by corona treatment and alkali treatment to reveal the effects of different treatments on the surface activity of RSP. The infiltration height method was applied to evaluate the variation of surface activity. The alkalized samples of RSP with different densities were prepared by using sodium hydroxide solution with pH value of 8∼14. The samples of different densities were then subjected to corona treatment under high purity oxygen conditions with treatment power of 50 W, 100 W, 300 W, and 500 W and with a time of 4 min or 7 min. The surface activity of the treated specimens was evaluated by measuring the absorption properties of three kinds of liquids by infiltration-height method: distilled water, glycerin, and alcohol. The results revealed the following. (1) After alkalization treatment, the surface absorption performance of RSP for these three liquids was improved, and it increased with the increase of pH value of the treatment solution. The suitable pH value of the alkalized solution for RSP is 7∼11, which can improve the surface absorption performance. (2) After corona treatment, the surface absorption performance of RSP increased with the increase of corona treatment power. RSP had the highest surface absorption performance for alcohol. With the density of RSP increased, the surface absorbability slightly decreased. Therefore, it is not suitable to utilize corona treatment in improving absorption for the higher density RSP. At the same time, with the variation of corona treatment time, the absorption of RSP surface changed irregularly because of the polarity of different test liquids. (3) The reasonable parameters of alkalization treatment and corona treatment are beneficial in improving the gluability of RSP. These results have guiding significance for RSP surface decoration process.

Surface Density Gradient Engineering Precedes Enhanced Diffusion; Drives CMOS In-Line Process Flow Compatible Cu–Cu Thermocompression Bonding at 75 °C

Diffusion is one of the most critical and key factor for achieving low temperature and low pressure thermocompression bonding. In this work, we propose a novel concept of modifying density conditions within the Cu films. The density of film was varied by varying the DC bias applied for the sputter deposition. While two samples of different densities are brought in contact with each other, Cu atoms from the thin film having higher density of atoms tends to interdiffuse into the thin film having lower density. Optimal dc biasing conditions for pair of wafers were figured out based on the pre-bonding characterizations and it yielded an excellent bonding at Sub 100 °C. No observable bond interface X-TEM images and bond strength of 164 MPa confirmed the quality of bonding. Furthermore, bonded structure undergone various reliability tests include multiple current stressing test, temperature cycling test and relative humidity test confirms Cu-Cu bonding using surface density gradient engineering is stable and promising candidate for future 3D IC integration applications.

Changes in characteristics of wood fiber insulation board according to density

As the demand increases for low energy green buildings, such as passive housing, the development of new insulation systems based on natural materials is underway. In this study, 20-mm-thick wood fiber insulation board (WIB) samples of different densities were prepared using melamine-formaldehyde-urea (MFU) resin adhesives. The resin contents were fixed at 35% and the target densities were 0.10 g/cm3, 0.15 g/cm3, 0.20 g/cm3, and 0.25 g/cm3. The thermal conductivities of the WIBs gradually increased as the density increased. The formaldehyde (HCHO) emissions of all the WIBs indicated that they were of “Super E0” (SE0) grade, but the quantity of the HCHO emissions slightly increased as the density increased. The thickness swelling of all the WIBs was stable at less than 3%, and the bending strength linearly increased as the WIB density increased. A notable decrease in the water absorption rate was observed between the lower and higher density WIB samples. Based on the results of the cone calorimeter tests, the carbonization depth ratio and the weight loss rate remarkably decreased as the density increased. Therefore, the optimum WIB density was in the range of 0.15 g/cm3 to 0.20 g/cm3 to provide adequate insulation performance as well as human and structural safety.

Isochoric thermal conductivity of solid 2-propanol

The isochoric thermal conductivity of solid 2-propanol (C3H7OH) was measured for samples of different densities, in the temperature range from 140 K up to melting. It was found that thermal expansion significantly affects the temperature dependence of thermal conductivity in monohydric alcohols studied at pre-melting temperatures. The isochoric thermal conductivity of all samples decreased with increasing temperature weaker than at a saturated vapor pressure, and deviates strongly from the k ∝ 1/T dependence. We describe the experimental results in the framework of a model involving thermal transfer by the propagons and diffusons; further, we discuss its principled difference from the simple Debye model, which does not take into account the dispersion and real density of phonon states. The contributions of propagons and diffusons in 1-and 2-propanol are calculated, and a comparison of thermal conductivities of isomers performed. It was found that the contribution of the diffusons is much higher than that of the propagons, and, in 2-propanol, both contributions are significantly smaller than in 1 - propanol. It was shown that the coefficients Ai responsible for the contribution of the propagons were essentially dependent on the density, while the coefficients Bi describing the contribution of the diffusons were practically constant.

Continuum cavity expansion and discrete micromechanical models for inferring macroscopic snow mechanical properties from cone penetration data

AbstractDigital cone penetration measurements can be used to infer snow mechanical properties, for instance, to study snow avalanche formation. The standard interpretation of these measurements is based on statistically inferred micromechanical interactions between snow microstructural elements and a well‐calibrated penetrating cone. We propose an alternative continuum model to derive the modulus of elasticity and yield strength of snow based on the widely used cavity expansion model in soils. We compare results from these approaches based on laboratory cone penetration measurements in snow samples of different densities and structural sizes. Results suggest that the micromechanical model underestimates the snow elastic modulus for dense samples by 2 orders of magnitude. By comparison with the cavity expansion‐based model, some of the discrepancy is attributed to low sensitivity of the micromechanical model to the snow elastic modulus. Reasons and implications of this discrepancy are discussed, and possibilities to enhance both methodologies are proposed.

Influence of saturation on rainfall generated landslides in shale along Murree-Kohala road, Pakistan

On August 10, 2010 a series of landslides of more than 90,000 m3 occurred along the Muree-Kohala road in the northern area of Pakistan. A study was undertaken to evaluate the likely impacts of percent saturation and bulk density on mobilized shear strength along the basal rupture surface of the landslide. A series of unconfined compression test and unconsolidated undrained triaxial tests were performed on remolded samples of different densities with varied percentages of saturation. The results of these tests suggest that soil cohesion and friction decreases with increasing saturation. The tests also showed that the shear strength parameters tend to increase with increasing dry density; however, all the samples exhibited a noticeable loss of shear strength with increasing degree of saturation, independent of soil density.

Moisture content measurements in wood using dual-energy CT scanning – a feasibility study

ABSTRACTCurrently computed tomography (CT) scanning provides a non-destructive method to determine moisture content in wood in three dimensions. With the current methodology two measurements are needed, one with the scanned piece of wood’s moist state and one after drying. Then the difference of the images can be calculated. The drawback and challenge is that dimensional changes due to shrinkage of wood in the drying process have to be compensated for by image processing. In this study a dual-energy CT scanning method is tested based on the consecutive scanning of wood samples at different energy levels to differentiate water from wood, without the necessity to dry the sample and thus without the need for complex image correction. Not quantified but visible differentiations due to moisture content were obtained on small cubical pine samples of different densities by quick consecutives scans at 60 and 200 kV. The results suggest that given that the pixels in the CT images are representing absorption coefficients it should be possible to directly measure moisture content in wood non-destructively in small volume elements inside solid wood in three dimensions. Further applications of this technique in industrial CT scanning of wood are discussed.

Investigation of mud density and weighting materials effect on drilling fluid filter cake properties and formation damage

Drilling fluid density/type is an important factor in drilling and production operations. Most of encountered problems during rotary drilling are related to drilling mud types and weights. This paper aims to investigate the effect of mud weight on filter cake properties and formation damage through two experimental approaches. In the first approach, seven water-based drilling fluid samples with same composition are prepared with different densities (9.0–12.0 lb/gal) and examined to select the optimum mud weight that has less damage. The second approach deals with investigating the possible effect of the different weighting materials (BaSO4 and CaCO3) on filter cake properties. High pressure/high temperature loss tests and Scanning Electron Microscopy (SEM) analyses were carried out on the filter cake (two selected samples).Data analysis has revealed that mud weigh of 9.5 lb/gal has the less reduction in permeability of ceramic disk, among the seven used mud densities. Above 10.5 ppg the effect of the mud weight density on formation damage is stabilized at constant value. Fluids of CaCO3-based weighting material, has less reduction in the porosity (9.14%) and permeability (25%) of the filter disk properties than the BaSO4-based fluid. The produced filter cake porosity increases (from 0.735 to 0.859) with decreasing of fluid density in case of drilling samples of different densities. The filtration loss tests indicated that CaCO3 filter cake porosity (0.52) is less than that of the BaSO4 weighted material (0.814). The thickness of the filter cake of the BaSO4-based fluid is large and can cause some problems.The SEM analysis shows that some major elements do occur on the tested samples (Ca, Al, Si, and Ba), with dominance of Ca on the expense of Ba for the CaCO3 fluid sample and vice versa. The less effect of 9.5 lb/gal mud sample is reflected in the well-produced inter-particle pore structure and relatively crystal size. A general recommendation is given to minimize the future utilization of Barium Sulfate as a drilling fluid.

A new approach for obtaining settling velocity in a thickener using statistical regression: A case study

In this research work, the parameters affecting the settling velocity within the thickeners were studied by introducing an equivalent shape factor. Several thickener feed samples of different densities including copper, lead and zinc, and coal were prepared. The settling tests were performed on the samples, and the corresponding settling curves were plotted. Using the linear regression analysis, the Chein's equation was fitted to the experimental data in order to obtain the equivalent shape factors for the different minerals. Moreover, the relations between the equivalent shape factors and the settling parameters were investigated. The R-squared values for the fits proved the capability of the Chein's equation to fit well on the experimental data (0.96R 2 0.99 for the copper sample, 0.96R 2 0.98 for the lead and zinc sample, and 0.93R 2 0.97 for the coal sample). The results obtained showed that the equivalent shape factor generally decreased with increase in the initial solid concentration. The equivalent shape factor for the coal sample in the samples with concentrations higher than 25% was negative but close to zero. This unusual behavior was explained by discussing the effects of the flocculants on the formation of the network structure in these samples. Determination of the equivalent shape factors would be an invaluable achievement in mineral processing. The researchers can simply put these factors into the Chein's equation to calculate the settling velocity of the minerals instead of performing expensive and time-consuming experiments.

Mechanical behaviour of dental implants

Dental implants are in general made of titanium, since this material promotes a stable and functional connection between the bone and the surface of the implant. Efforts produced during the chewing cycles may interfere with this union, affecting the process of osseointegration and eventually compromising the stability of the implant.Given the difficulty in working with bone in vivo, in the present study two implant systems were inserted in polymer samples, known as Sawbones, which simulate the structure of trabecular bone. The performance of the implants was evaluated through experimental fatigue tests. The qualitative analysis of the damage in the structure of the samples was performed using scanning electron microscope images. Determination and comparison of stress fields and deformations at the Sawbone-implant interface using an analytical model of indentation and the finite element method (FEM) to model indentation and penetration were undertaken.The experimental results showed that the performance of the Morse taper implant was greater than the external hexagonal implant when both were tested cyclically in samples of different densities. It was shown that the diameter, length, density and type of implant-abutment interface affected the behaviour of the implants. The numerical results of indentation model were very similar to those obtained by the analytical model. The results of the FEM penetration model had the same tendency as the experimental values and the indentation analysis with increasing the density of the polymer foam. It could be concluded that, as in foams, the increase of the bone density will induce an increased stability to the implants.