Minimum Void Research Articles

Selection of Process Parameters for Near-Net Shape Deposition in Wire Arc Additive Manufacturing by Genetic Algorithm

In wire arc additive manufacturing (WAAM), deposition of multiple beads in multiple layers is required for fabricating any component. This article presents ways to optimize the selection of parameters for near-net shape deposition to minimize void and excess material in WAAM by GA. Initially single-bead geometry model was developed utilizing response surface methodology and experiments were conducted utilizing Box-Behenken design of experiments for deposition of 304L stainless steel in WAAM. Bead geometry parameters, i.e., bead width, bead height and bead cross-sectional area, etc., were expressed in terms of the process parameters like voltage, wire feed rate, torch speed and gas flow rate. Optimal processing conditions and deposition planning were determined utilizing a GA to minimize void and maximize material yield. The proposed approach was validated through deposition of three shapes, i.e., slice, wall and block. The three shapes fabricated with optimal parameters were found to have minimum void and maximum material yield. It has been revealed that optimal bead sizes and degree of overlapping are different for fabricating different geometries. Mechanical testing and metallurgical characterization of the deposited materials exhibited comparable properties of the deposited material to that of the base material. Moreover, double wire feed deposition was seen to deliver higher deposition rate and superior mechanical properties of the deposited material compared to the single wire feed deposition.

Mechanical Properties of High Calcium Flyash- GGBFS Geopolymer Paste, Mortar and the Effect of Glass Fibre Mesh on the Strength of Geopolymer Mortar Tile

In this paper, a combination of high-calcium fly ash (HCFA) and ground granulated blast furnace slag (GGBFS) was used along with a combination of sodium hydroxide (NaOH) and sodium silicate(Na2SiO3) as alkaline activators (AAs) to produce geopolymer paste and mortar. The alkaline activator ratio (AAR) was maintained at 1.5 apart from their molarity at 10 for the study. A rational method, namely minimum voids approach was used for the mix design. A commercially available glass fibre mesh was used as reinforcement in the geopolymer mortar produced above, to assess its potential for use as a flooring tile. The influence of W/S (water-to-solids) ratio and the influence of various fine aggregates, namely, river sand (R), manufactured sand (M) and construction demolition waste (D) on the various geopolymer system (GP) and on the strength characteristics, are highlighted. A maximum transverse strength (TS) of 6.25 N/mm2 could be attained by the geopolymer tile, using three layers of glass fibre mesh and GP mortar developed. The study indicates that a combination of FA and GGBFS helps us to attain substantial strength under ambient temperature in geopolymer mortar.

Influence of particle shape and size on the threshold fines content and the limit index void ratios of sands containing non-plastic fines

Although several empirical and analytical models are available to predict the threshold fines content (fthr) for sand-silt mixtures, none of them considers the combined effects of particle shape and size. In view of this, the current paper proposes a method to estimate the threshold fines content and the minimum void ratios for sand-silt mixtures at various contents of non-cohesive fines incorporating both parameters. The results of laboratory experiments along with existing data from literature, both for combinations of host and fine materials with various shapes and sizes were used in the analysis. The particle shape is represented through the particle regularity, ρ for both host and fine materials whereas the size is represented through the particle size ratio, χ. Empirical relations for the threshold fines content and the minimum void ratios at different fines contents were formulated, and proven to perform satisfactorily well over a wide range of particle shapes and sizes. In addition, the new empirical equations were validated by means of a comparison with existing results from literature.

Thermal Conductivity of Granular Soil Mixtures with Contrasting Particle Shapes

Particle shape is known to affect the mechanical behavior of sands because it influences packing density and particle contacts. Even though the thermal conductivity of sands also depends on packing density and particle contacts, the effects of particle shape on thermal conductivity are not well understood. A series of thermal needle tests were conducted on five granular soil mixtures with different proportions of rounded and angular glass particles having the same mineral composition and gradation. The maximum and minimum void ratios and the packing density of these mixtures were found to depend on the overall regularity, defined as the average value of the particle’s aspect ratio, convexity, and sphericity. For a given overall regularity, the thermal conductivity increases with decreasing void ratio or increasing relative density. Interestingly, the overall regularity has a small effect on the thermal conductivity at a given void ratio but has a significant effect on the thermal conductivity at a given relative density. A particle shape–dependent empirical equation is proposed to quantify the effects of relative density and overall regularity on the thermal conductivity of the tested sand.

14: Voiding assessment based on minimum spontaneous void of 150 mL compared to retrograde fill method after female pelvic floor procedures: A randomized controlled trial

14: Voiding assessment based on minimum spontaneous void of 150 mL compared to retrograde fill method after female pelvic floor procedures: A randomized controlled trial

3D printed continuous CF/PA6 composites: Effect of microscopic voids on mechanical performance

The production of continuous carbon fibre composites using a fused deposition modelling (FDM) method has addressed the problem of low mechanical performance of raw- or short-fibre reinforced polymer parts fabricated by the same process, due to the excellent specific strength and stiffness of continuous fibres. However, one key issue of 3D printed polymers or fibre-reinforced polymers is the formation of microscopic voids between individual filaments and within the filaments during the FDM process. This study aims to quantify the adverse effects of voids on 3D printed continuous fibre-reinforced polymer composites. Optical microscopy and micro-CT are used to quantify the void content in continuous CF/PA6 composites fabricated on a 3D printing platform. As a benchmark, 3D printed CF/PA6 composites with the same printing configurations were further processed by compression moulding (CM) with thickness controlled to achieve the minimum void content. Apart from tensile and three-point bending tests in the longitudinal and transverse directions, the study also evaluated the Mode I interlaminar fracture toughness of CF/PA6 composites. By revealing the substantial adverse effects of the microscopic voids in 3D printed composites, this study articulates the critical importance of developing in-process techniques during 3D printing to decrease the void content within the continuous fibre reinforced composites, for the sake of expanding practical applications of 3D printed continuous fibre composites.

Effects of the ratio between body forces and inter-particle forces on maximum void ratio

Relative density has been shown to be useful for interpreting soil behaviour and for estimating the strength and other soil characteristics in geotechnical engineering. Previous studies have shown that the index void ratios (maximum and minimum void ratios) used to determine relative density depend on the particle shape and the shape of the grain size distribution. However, the effect of the median grain size on the index void ratios has not been resolved. In this study, the effects of the particle weight and the particle size relative to the inter-particle attractive forces are examined by conducting maximum void ratio (emax) tests in elevated gravity fields through the use of a centrifuge. The results indicate that both an increasing particle size and increasing gravity affect emax, providing evidence that inter-particle forces affect the packing of materials in this limit state. The change in emax, occurring in an elevated gravity field, implies that the relative densities estimated for centrifuge model experiments may not be accurate.

Using grain size to predict engineering properties of natural sands in Pakistan

Laboratory determination of strength and deformation behavior of clean sands and gravels has always been challenging due to the difficulty in obtaining their undisturbed samples. An alternative solution to this problem is to develop correlations between mechanical properties of cohesionless soils and their gradation characteristics. This study presents database of 3 natural sands with 11 varying particle size gradation curves to allow investigating relationships between mean particle size, maximum and minimum void ratio, relative density and shear strength of the test soils. Direct shear tests were performed at relative densities of 50, 75 and 95% to explore the effects of gradation and density on the angle of internal friction of the modeled sand samples. It is found that the mean grain size D50 bears good correlations with void ratio range (emax - emin) and peak angle of internal friction Φ\'peak. The generated regression models are in good agreement with published literature and can be considered as reliable for natural sands in Pakistan. These empirical correlations can save considerable time and efforts involved in laboratory and field testing.

Prediction Model of Minimum Void Ratio for Various Sizes/Shapes of Sandy Binary Mixture

The minimum void ratio is a fundamental physical index for evaluating particle properties in soil mechanics, ceramic processing, and concrete mixes. Previous research found that both particle size distribution and particle shape characteristics would affect minimum void ratio, while the current research generally uses a linear model to estimate the minimum void ratio of a binary mixture, ignoring quantitative effect of particle shape on the minimum void ratio. Based on a study of binary mixtures of natural sand from three different origins and iron particles of two different shapes, this paper analyzes the influence factors of the minimum void ratio, and a quadratic nonlinear model is proposed for estimating the minimum void ratio of binary mixture. The model contains only one undetermined coefficient, a, the value of which is correlated to the particle sphericity, particle size, and particle size ratio. A theoretical calculation formula for the coefficient a is proposed to quantitatively analyze the effects of these three factors on the size of the parameters. In the end, the model is used to estimate the minimum void ratios of sand and substitute particles from different producing areas; the average difference between the estimated values and the fitted values is about 2.03%, suggesting that the estimated values of the model fit well with the measured data.

Evaluation of compressive strength and void content of resin based dental composites

Resin based dental composites are quite popular for tooth restoration. In this article, BisGMA and TEGDMA were mixed to make resin matrix. For photo-polymerization, Camphorquinone was used and DMAEA was used as accelerator. Silica was employed as filler in different %wt (0%, 3%, 6% and 9%). The samples were tested for compressive strength and void content. This study reveals experimentally that introduction of silica in dental resin significantly increasing compressive strength and void content of resin based dental composite. Maximum compressive strength of 150.47 MPa was found at 9%wt of silica and minimum void content of 0.89% were found at 3%wt of silica as filler in dental composite.

Effect of grain size distribution on the maximum and minimum void ratios of granular soils

The maximum and minimum void ratios define the loosest and densest conditions of a granular soil. Correlations with some granulometric properties of soil are of interest for practical applications, but the experimental procedure to determine these variables can be time consuming. In this work the influence of the grain size distribution on the maximum and minimum void ratios is investigated. Twenty different granular soils with varying grain size distributions were prepared and tested. The experimental results, together with a compilation of 56 additional results reported in the literature, are statistically analysed. The analysis is conducted to examine the influence of some granulometric properties (D10, D30 and D60) on the maximum and minimum void ratios. As a result, some correlations considering the aforementioned variables are proposed. Subsequently, it is shown that the proposed correlations have better agreement with the experimental data than other proposals reported in the literature. The paper ends with some concluding remarks.

Laboratory and field investigations in granular soils to correlate relative density, relative compaction and grain size

An attempt has been made to correlate relative density and relative compaction based on laboratory and field test data. In this investigation, 185 sandy soil samples were tested in the laboratory. The experimental investigations include classification tests, maximum and minimum density tests, and standard and modified Proctor and in-situ density tests. The values of the dry unit weight of these samples obtained by performing different tests fall between 14.7 kN/m3 and 20.8 kN/m3. Based on these results, linear and multivariate regression analyses were carried out to (a) relate relative compaction and relative density, (b) relate maximum (emax) and minimum void ratios (emin), and (c) express emax and emin in terms of median grain size (D50) and uniformity coefficient (Cu). Experimental and predicted values varied ± 5%, with a 95% confidence interval for the relation between relative compaction and relative density, and for other relations the variation was ± 10%. The proposed equations were validated using a new data set which had not been used for the development of the correlations. Proposed equations were also compared with equations presented by various other researchers. Validation of the proposed equations suggests that these equations may be used for future prediction of the respective variables.

The critical state line of nonplastic tailings

The probability of failure of tailing dams and associated risks demand improvements in engineering practice. The critical state line provides a robust framework for the characterization of mine tailings. New experimental data for nonplastic platinum tailings and a large database for tailings and nonplastic soils (grain size between 2 and 500 μm) show that the critical state parameters for nonplastic tailings follow the same trends as nonplastic soils as a function of particle-scale characteristics and extreme void ratios. Critical state lines determined for extreme tailings gradations underestimate the range of critical state parameters that may be encountered in a tailings dam; in fact, mixtures with intermediate fines content exhibit the densest granular packing at critical state. The minimum void ratio emin captures the underlying role of particle shape and grain size distribution on granular packing and emerges as a valuable index property to inform sampling strategies for the assessment of spatial variability. Mineralogy does not significantly affect the intercept Γ100, but it does affect the slope λ. The friction coefficients M of tailings are similar to those of other nonplastic soils; while mineralogy does not have a significant effect on friction, more angular grains lead to higher friction coefficients.

Investigation and characterization of ultrasonically welded GF/PA6T composites

High-performance polyamides (HPPA) matrix composite meets the demanding requirement of automotive thermal management applications as a replacement to conventional metals. Effective joining of such composites are still a challenge and a better understanding of material performance upon joining are needed. This research study investigates the behavior of glass filled semi-crystalline and partially aromatic polyamide composite upon ultrasonic plastic welding. Welding process parameters were experimentally realized for a quality weld in shear type joint configuration. A weld strength of 3.1 kN was achieved. Material performance, thermal transition, degradation temperature, mass loss and morphology near welding zone were evaluated by advanced characterization techniques. A decrease in glass transition temperature (Tg) and change in material crystallinity were observed. The morphology of welded interface reveals minimum void formation. Negligible amount of weight loss was observed after welding with a degradation temperature much higher than material melting point, suitable for high temperature applications.

Nonlinear estimation model of minimum void ratio for sand–silt mixtures

Previous experimental studies on sand–silt mixtures have shown that silty fines significantly affect the soil fabric and resulting mechanical behavior. Some bilinear models have been proposed to capture minimum and maximum void ratios. In this study, previously reported data from 37 soil mixtures including coastal sands with 338 individual specimens for which the minimum void ratios are available were studied. The results helped form the basis to develop a nonlinear model capable of estimating the shape of the minimum void ratio curve of the sand–silt mixtures. The equations of minimum void ratios were derived for soil mixtures in coarse and fine grain dominant regions. The results show that the predicted values of minimum void ratios by quadratic polynomial equations agree well with the measured data; the root mean square error is 0.03. The proposed model only requires one data point from the experimental test to predict the minimum void ratio for any soil mixture with various fine contents.

Minimum void ratio characteristic of soils containing non-plastic fines

The minimum void ratio is an index widely used to indicate the contraction characteristics and the densest state of soils. The minimum void ratio obtained by the traditional test method has been utilized to represent the density of soils irrespective of their fines content despite the restriction (FC ≤ 5%). By considering the effect of the blow count, pore water, and their primary properties, the applicability of the minimum void ratio to soils containing fines was examined with an automatic tapping machine. It was confirmed that the blow count of the traditional method is not sufficient for soils with a high fines content. Furthermore, the presence of pore water had a significant effect on the minimum void ratio of soils containing fines. The characteristics of the cyclic minimum void ratio, which indicates the minimum void ratio obtained throughout the repetition of liquefaction and drainage, were also examined.

Strength of Geopolymer Paste using a Ternary Blend of Fly Ash GGBFS and Silica Fume under Ambient Conditions

In this paper, compressive strength (CS) of geopolymer paste has been studied under ambient conditions using locally available Class C fly ash, GGBFS and silica fume and a combination alkali activator, namely: NaOH and Na2SiO3. Two approaches were used for mix proportioning and 60 mixes of the paste were proportioned. It is found that all the mixes proportioned were workable and no adverse effects were observed within 30 minutes of mixing. It is found that the ‘minimum voids’ approach along with a constant fly ash – to – activator ratio (FA/AA) is the best approach for the design of geopolymer mixes, rather than a constant water- to- solid ratio (w/s). Further, the role of GGBFS and SF on the CS of the paste has also been highlighted.

Digital Radiographic Evaluation of the Quality of Different Root Canal Obturation Techniques in Deciduous Mandibular Molars after Preparation with Rotary Technique.

Statement of the Problem: Several factors affect the success of pulp therapy of primary teeth, including cleaning and shaping of the root canals and the quality of obturation as the most important steps. Purpose: The aim of the present study was to compare the quality of different root canal obturation techniques in deciduous mandibular molars subsequent to preparation of the root canals with the rotary technique, using the photo stimulated phosphor (PSP) digital radiographic technique. Materials and Method: In this in vitro study, 221 root canals were selected in 80 extracted deciduous mandibular second molars. The root canals were prepared with a modified protocol for ProTaper NiTi rotary files and with only two instruments (SX and S2) and obturated using a lentulo spiral, condensation technique, an anesthetic syringe, and tuberculin syringe techniques with ZOE paste. The quality of the root canal obturation (obturation length and the number and sizes of the voids) was evaluated using PSP radiographic technique. Data were analyzed with SPSS 21, using chi-squared, Kruskal-Wallis and Mann-Whitney tests. Results:There were no significant differences in the obturation length (p= 0.285) and the number of voids (p= 0.061) between the study groups; however, there were significant differences in void sizes between the study groups (p= 0.001). The condensation and tuberculin syringe groups exhibited the best and worst results considering the obturation length, respectively. Lentulo and anesthetic syringe techniques have also exhibited acceptable results. The condensation and anesthetic syringe groups exhibited the minimum and maximum number of voids, respectively. The condensation and lentulo groups exhibited the maximum and minimum void sizes, respectively. Conclusion:If implemented correctly, there will be no significant difference among the experienced root canal obturation techniques considering obturation length and the number of voids.

Influence of curing condition on thermo-mechanical properties of fly ash reinforced epoxy composite

The effect of ambient, oven and microwave curing conditions on the thermo-mechanical properties of fly ash (FA) filled epoxy composites with four different volume fraction of fly ash mixed with five different mixing duration have been investigated. The thermal analysis of the composites was carried out in a differential scanning calorimeter (DSC) to determine the transitions, the amount of curing heat, the degree of cure (α) etc. The mechanical behaviour was evaluated from the tensile, flexural and impact characteristics of the specimens. The obtained results showed that the composite with 10%FA content mixed for 30 min has the minimum void fraction with a homogeneous mixture. DSC analysis clearly showed that the microwave cured specimen requires less heat energy to attain ~99% degree of crosslinking. The oven cured specimen with similar process variables had slightly higher Tg and Tm than the microwave cured specimens. Ambiently cured specimens generally had the lowest thermal properties with an insignificant degree of cure. The maximum tensile, flexural and impact properties were achieved with microwave cured specimen containing 10%FA mixed for 30 min followed by oven cured and ambient cured specimens of similar condition. Several non-linear equations have been developed to predict the responses (i.e. σs, σf and IJ) as a function of FA content and mixing time. The models are able to predict the responses adequately with more than 96% accuracy. The optimum values of FA content and mixing time are 10% and 30 min respectively were achieved by an optimization test in RSM.

Process optimization and stochastic modeling of void contents and mechanical properties in additively manufactured composites

The effects of process parameters (print temperature, bed temperature, and print speed) on dimensional accuracy, void contents, and mechanical properties are experimentally investigated for the additively manufactured short carbon fiber reinforced composites. Such studies are carried out at bead, lamina, and laminate levels to identify the process-microstructure-property relationship. Different dimensional parameters such as height, width, and deposition-alignment are monitored for different process parameters at the bead level and its effects on lamina, and laminate are studied in a multi-level manner. The various sources of uncertainties in fused filament fabrication (FFF) based additive manufacturing (AM) are identified, and their adverse effects on microstructure and performance are analyzed. Utilizing the experimentally extracted data for dimensional variability and mechanical property at each level, physical models were adopted to accurately quantify the uncertainty. A non-intrusive polynomial chaos (NIPC) based uncertainty analysis was introduced to improve the computational efficiency and reliability of the physical models. The classical lamination theory (CLT) is used with a slight modification to account for different kinds of voids of short fiber reinforced composites manufactured by FFF. The adjusted process parameters for 5% carbon fiber reinforced polylactic acid (CF/PLA) composite showed minimum dimensional variability and maximum structural performance at a print temperature of 220°C, bed temperature of 80°C, and print speed of 20 mm/s. The maximum dimensional accuracy, minimum void contents, and improved mechanical properties support these optimized processed parameters. These optimized parameters may be related to the viscosity of the material to identify the same parameters for other material systems. The NIPC accurately predicted intra-bead, inter-bead and interfacial-bead voids contents with the overall void contents in the range of 20–26%. All these predicted void contents were incorporated in the CLT to predict the stochastic load distribution of the laminate. The stochastic model closely predicted the laminate properties in terms of axial load distributions which were validated by experimentation of [00]s, [900]s, [450]s, [00/900]s, and [±450]s laminate testing.