Amount Of Voids Research Articles

A quasi-exponential distribution of interfacial voids and its effect on the interlayer strength of 3D printed concrete

In this work, a novel theoretical model of the void length probability distribution in 3D printed concrete is established based on a zigzag analog of the layer interface. A quasi-exponential distribution of void length is predicted and subsequently validated on both the zigzag analog and the actual 3D printed concrete, with different void ratios that determine the descending rate and node intervals that decide the horizontal scaling of the distribution. Moreover, the relationships between the interlayer strength, void ratio, and quantity of voids are also studied based on the theoretical model. It is found that the quantity of voids is symmetric about a void ratio of 0.5, and the decrease in the interlayer strength against the void ratio is non-linear which is approximated well by combined exponential and linear functions. This work is believed to reveal the nature of the interfacial void distributions and significantly advance the understanding of the layer interface in 3D printed concrete. The code for the zigzag analog with the computation of its interlayer strength is publicly available at: https://github.com/Human-HLW/Layer-interface.

Soldering Pressure Effect on Lifetime of Thermoelectric Modules under Thermal Cycling.

For practical industrial applications, enhancing the longevity and the reliability of thermoelectric modules (TEMs) is equally as crucial as improving their conversion efficiency. This study proposes a strategy for extending the lifespan and introduces the quality evaluation criteria for the most extensively used commercial bismuth telluride TEM. By varying the soldering pressure during module assembly, its impact on the quality of the module's internal interfacial connections was investigated, via analyzing its contact resistivity, shear modulus, and antifatigue ability through thermal cycling tests. The findings reveal that increasing the soldering pressure leads to a slight reduction in interfacial contact resistivity and has no significant effect on the shear modulus but notably enhances the module's antifatigue ability during thermal cycling tests. According to the SEM results, it can be evidently deduced that the aforementioned phenomena are directly correlated with the size and quantity of voids distributed in the solder layer, which is regarded as the origin of antifatigue ability. Thus, it can be inferred that augmenting the soldering pressure represents an effective approach to prolonging the lifespan of TEMs assembled by using the soldering method. Furthermore, the existence of voids within the solder layer can serve as a criterion for an initial assessment of module longevity. This study provides a reference for both the industrial assembly and lifespan evaluation of commercial bismuth telluride TEMs.

VALORIZATION OF DIVERSE SIZES OF COAL BOTTOM ASH AS FINE AGGREGATE IN THE PERFORMANCE OF LIGHTWEIGHT FOAMED CONCRETE

In recent years, research work on the use of coal bottom ash (CBA) as a partial alternative for aggregate in concrete is on the rise. This research is aimed at examining the characteristics of lightweight foamed concrete with CBA as fine aggregate to produce environmentally sustainable product. With the volume replacement technique, CBA was used as 25%, 50%, 75%, and 100% replacement for conventional mining sand with different sieve sizes of smaller than 4.75, 2.36, and 0.6 mm in concrete. Water absorption, porosity as well as mechanical characteristics tests, including compressive strength, splitting tensile strength, and modulus of elasticity (MOE) were conducted and analyzed. X-ray diffraction and scanning electron microscopy microstructural investigations were also performed to correlate test results. The quality of concrete was investigated using a non-destructive ultrasonic pulse velocity test. According to the findings, the highest replacement level of CBA with a sieve size smaller than 0.6 mm had an impact in reducing workability. The effect of CBA particles on water absorption, MOE, compressive strength, and tensile strength depends on the size of the fine aggregate, the replacement ratio and the density. In general, substituting mining sand with CBA aggregate improved the mechanical performance of concrete, notably for the aggregate size of less than 0.6 mm. Moreover, the SEM images indicate that the addition of CBA particles decreased the size and quantity of voids in the foamed concrete.

Natural Rubber Blend Optimization via Data-Driven Modeling: The Implementation for Reverse Engineering.

Natural rubber formulation methodologies implemented within industry primarily implicate a high dependence on the formulator’s experience as it involves an educated guess-and-check process. The formulator must leverage their experience to ensure that the number of iterations to the final blend composition is minimized. The study presented in this paper includes the implementation of blend formulation methodology that targets material properties relevant to the application in which the product will be used by incorporating predictive models, including linear regression, response surface method (RSM), artificial neural networks (ANNs), and Gaussian process regression (GPR). Training of such models requires data, which is equal to financial resources in industry. To ensure minimum experimental effort, the dataset is kept small, and the model complexity is kept simple, and as a proof of concept, the predictive models are used to reverse engineer a current material used in the footwear industry based on target viscoelastic properties (relaxation behavior, tan, and hardness), which all depend on the amount of crosslinker, plasticizer, and the quantity of voids used to create the lightweight high-performance material. RSM, ANN, and GPR result in prediction accuracy of 90%, 97%, and 100%, respectively. It is evident that the testing accuracy increases with algorithm complexity; therefore, these methodologies provide a wide range of tools capable of predicting compound formulation based on specified target properties, and with a wide range of complexity.

Characterisation of void and fiber distribution in 3D printed carbon-fiber/PEEK using X-ray computed tomography

A detailed analysis of the microstructure of five 3D printed CF/PEEK samples and the commercial feedstock material used to produce them has been conducted by the means of state-of-the-art micro-CT imaging. The images unequivocally show that both feedstock filament and printed samples contain a large quantity of voids heterogeneously distributed. Voids are randomly distributed within the feedstock, while they are aligned in rows parallel to the mould plate within the printed samples. Short fibers are heterogeneously distributed and display a preferential alignment in all specimens. Overall, the results showed that the 3D printing process did not remove the voids originally present in the feedstock filament and varying key printing parameters had only a minor effect on the printed samples’ void content, while the depositional nature of the printing process strongly affected the samples’ internal geometry.

Evaluation of Fracture Strength and Total Void Amount in Composite Restorations on Endodontically Treated Teeth

Objective: The aim of the study was to investigate the fracture strength of different composite resins and the quantity of voids in conventional posterior composite, high-flow flowable composite, bulk-fill flowable composite, and fiber-reinforced composite. Materials and Methods: Forty-four caries-free, freshly extracted mandibular premolars were used for this study. Teeth were prepared for cavity and root canal treatment. Subsequently, root canal treatment was applied to the teeth and cavities in order to prepare them for restorations. The specimens were then divided into four groups: group-1: Estelite Posterior; group-2: Estelite Flow Quick High Flow; group-3: Estelite Bulk-fill Flow; group-4: everX Posterior. One specimen from each experimental group was examined using micro-CT to perform measurement of voids. Results: The fracture strength values of high-flow flowable, bulk-fill flowable, fiber-reinforced, and conventional micro-hybrid composites were found to be similar (p=0.497). EverX Posterior showed the highest fracture strength values (841.1±149.4 N), followed by Estelite Bulk-fill Flow (822.8±170.8 N). Conclusion: Volume of voids (%) obtained from Micro-CT analysis revealed that restorations with high-flow liner or bulk-fill flowable exhibited more voids. The fiber-reinforced composite showed the lowest percentage volume of incorporating voids and the highest fracture strength results.

Evaluation of Printing Parameters on Porosity and Mechanical Properties of 3D Printed PLA/PBAT Blend Parts

AbstractFused deposition modeling (FDM) is a rapidly growing additive manufacturing technology due to its ability to manufacture complex‐shaped parts in a simple process. FDM parts present inherent porosity due to the fabrication process. The mechanical performance of the built part depends on controlling several printing parameters of the specimen and the quantity of voids. PLA/PBAT [polylactic acid/poly(butylene adipate‐co‐terephthalate)] blend is a biodegradable polyester with bio‐based content that is used as a potential replacement for conventional petroleum‐based polymers. PBAT reduces the stiffness and improves the tear strength of PLA. There is a lack of research on PLA/PBAT 3D printed parts, especially the relationship between flexural mechanical properties and porosity of PLA/PBAT parts. The aim of this work is to investigate the effect of layer thickness (LT), deposition speed (DS), and printing direction (PD) on porosity and flexural properties of PLA/PBAT blend parts. Experimental design method is used to identify the set of parameters, which gives optimized results. Specimens fabricated with lower printing parameter values allowed obtaining parts with less porosity and consequently improved bending properties.

Effect of air-blowing temperature and water storage time on the bond strength of five universal adhesive systems to dentin.

The purpose of this study was to evaluate the air-blowing temperature and water storage time on the micro-tensile bond strength (μTBS) of five universal adhesive systems to dentin. The bond strength with two different air-blowing temperatures (60±2ºC and 23±2ºC) was measured after water storage at 37ºC for 24 h and 100 days respectively. The fracture surface on dentin side was observed by scanning electron microscope (SEM). Three-way ANOVA revealed a significant effect of universal system (p<0.001) and air-blowing temperature (p<0.001) on bond strength to dentin except water-storage time (p=0.145). The interaction within three factors was significantly different (p<0.001). It could be concluded that the μTBS of universal systems to dentin was material-depended. The higher and more stable bonding performance of universal systems on dentin could be achieved by air-blowing at 60±2ºC temperature. In addition, the quantity of voids in the adhesive layer of aceton-based universal adhesive was significantly reduced by higher temperature.

A Study on the Mechanical Behavior of Jute-Epoxy Laminated Composite and its Hybrid

This study was designed to examine the consequences of lamination sequence, fiber orientation and hybridization on tensile, flexural, physical, and inter-laminar properties of Jute-epoxy laminated composites and its hybrid. These laminates are partially biodegradable hence environment-friendly. Here six laminated specimens were fabricated using hand lay-up techniques with 4 layers of fiber or 40% fiber loading as per the ASTM standard. Samples were prepared with three different orientation of 00, 300 and 600 to the loading direction. The experimental outcome revealed that composite with 300 fiber orientation gives a better result in flexural, microhardness, and interlaminar shear strength. Generally, Final failure was due to delamination, fiber pull-out, fiber failure or matrix cracking. Scanning electron micrographs were used for improved understanding of fracture mechanics. A substantial quantity of voids, improper alignment, fiber waviness and heterogeneous interface were found resulted in premature failure.

Health Promotion through Integrative Health Practices

In this work, in situ bi-phase (TiB2-TiCxNy)/(Ni-Ta) cermets were fabricated via a combined combustion synthesis and hot-pressing (CSHP) method in a Ni-Ti-BN-B4C-Ta system. The effects of Ta addition on the reaction process, phase constituents, microstructures and mechanical properties of the (TiB2-TiCxNy)/(Ni-Ta) cermets were studied. Ta is shown to dilute the system and lead to a small number of intermediate phases (Ni20Ti3B6 and Ni3Ti) that are retained in the products. Furthermore, the addition of Ta can markedly refine the ceramic particles and decrease the size and quantity of voids. The evaluation of the mechanical properties revealed that an increase in the Ta content resulted in increases in the compression strength (σUCS) and hardness and that the fracture strain (εf) increased first and then decreased. The cermet with the optimal addition of 5 wt% Ta possessed the best mechanical properties without decreasing the value of εf (2.9%). The addition of 5 wt% Ta resulted in a compressive strength of 3.37 GPa and the highest hardness of 1909 Hv, which is an increase of ~16% and ~22%, respectively, compared to cermets without added Ta.

Effect of Ta addition on the microstructures and mechanical properties of in situ bi-phase (TiB2-TiCxNy)/(Ni-Ta) cermets

In this work, in situ bi-phase (TiB2-TiCxNy)/(Ni-Ta) cermets were fabricated via a combined combustion synthesis and hot-pressing (CSHP) method in a Ni-Ti-BN-B4C-Ta system. The effects of Ta addition on the reaction process, phase constituents, microstructures and mechanical properties of the (TiB2-TiCxNy)/(Ni-Ta) cermets were studied. Ta is shown to dilute the system and lead to a small number of intermediate phases (Ni20Ti3B6 and Ni3Ti) that are retained in the products. Furthermore, the addition of Ta can markedly refine the ceramic particles and decrease the size and quantity of voids. The evaluation of the mechanical properties revealed that an increase in the Ta content resulted in increases in the compression strength (σUCS) and hardness and that the fracture strain (εf) increased first and then decreased. The cermet with the optimal addition of 5 wt% Ta possessed the best mechanical properties without decreasing the value of εf (2.9%). The addition of 5 wt% Ta resulted in a compressive strength of 3.37 GPa and the highest hardness of 1909 Hv, which is an increase of ~16% and ~22%, respectively, compared to cermets without added Ta.

Finite Element Limit Analysis of the Bearing Capacity of Strip Footing on a Rock Mass with Voids

Finite element limit analysis (FELA) was used to investigate the bearing capacity of strip footing on a rock mass with single or multiple continuous voids. The underlying rock mass was assumed to have perfect plasticity and obey the modified Hoek–Brown criterion. A sensitivity study relevant to the material constants, such as intact rock strength, unit weight, and geological strength index, was also conducted; in addition, some other geometric parameters, including the location, size, width, height, and quantity of voids, were addressed. The results include presentations of a series of design charts and descriptions of the failure mechanisms.

Experimental fatigue behavior of pultruded glass fibre reinforced polymer composite materials

Abstract The aim of this research is to investigate the behavior of pultruded Glass-fiber Reinforced Polymer (GFRP) composite materials subjected to fatigue loads. Static tests were performed to estimate the material strength and modulus of elasticity. Constant-amplitude axial tension-tension fatigue tests were conducted with a cyclic stress ratio of R = 0.1 and a frequency of 4Hz in order to establish fatigue life characteristics (S-N curve) and identify damage evolution and failure modes for the composite material. Generally, the damages developed in fatigue tests were characterized primarily by cracks in the matrix, followed by possible delamination of the material layers and finally the fiber failure and the specimen rupture. Tomography images were used to better understand the architecture of the composite material. It was observed that the layers of the fibers are not perfectly aligned and uniform and there is a substantial quantity of voids resulting in a very heterogeneous material which can explain the scatter of the experimental results.

Role of W in W/Ni Bilayer Ohmic Contact to n-Type 4H-SiC From the Perspective of Device Applications

Ohmic contacts to n-type 4H-SiC using Ni layer and W/Ni bilayer were investigated and compared. The phase composition, electronic states, and carbon structural evolution of the contact layer were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The surface roughness and cross-sectional morphology were characterized by atomic force microscopy and high-resolution transmission electron microscopy. The Keithley 4200-SCS semiconductor parameter analyzer was used to measure the current–voltage curves of the contacts. The specific contact resistance $\rho _{c}$ was calculated based on the circular transmission line model. $\rho _{c}$ is $\textsf {3.2}\times \textsf {10}^{-\textsf {5}}\,\,\Omega \cdot $ cm2 for W/Ni/SiC and $\textsf {4.2} \times \textsf {10}^{-\textsf {4}} \,\,\Omega \cdot $ cm2 for Ni/SiC. Ni2Si with minor W substitution and tungsten carbide with minor Ni substitution were identified as the dominant phases for W/Ni/SiC after annealed. The contact surface morphology is improved, and the content of free carbon and the quantity of voids at the interface are reduced when W is introduced into Ni/SiC. The wire bonding is easy to carry out and the thermal stability of ohmic contact is greatly enhanced. From the perspective of device applications, W/Ni bilayer ohmic contact to n-type 4H-SiC is very competitive.

Effects of La3+ doping on the crystal structures, densities, microstructures and thermosensitive characteristics of the LaxBa1−xCoO3−δ (0 ≤ x ≤ 0.1) ceramics for low temperature NTC resistances

In this work, polycrystalline LaxBa1−xCoO3−δ (0 ≤ x ≤ 0.1) ceramic samples were prepared by conventional solid-state reaction process. La3+ doping effects on the crystal structures, densities, microstructures and thermosensitive characteristics of the LaxBa1−xCoO3−δ ceramics were investigated. The major phase presented in the sintered samples is a hexagonal perovskite BaCoO2.6 phase. The doping of La3+ reduces the quantity of voids and improves the densities of the LaxBa1−xCoO3−δ ceramics compared with La-free ceramic. The resistivities of the LaxBa1−xCoO3−δ ceramics decrease exponentially with increasing temperature in each of the range of 10–26 K and 26–100 K. The resistivities and B constants increase as the contents of La3+ increase in the LaxBa1−xCoO3−δ ceramics.

Damage characterization of high-strength multiphase steels

High-strength steels show an entirely different material behavior than conventional deep-drawing steels. This fact is caused among others by the multiphase nature of their structure. The Forming Limit Diagram as the classic failure criterion in forming simulation is only partially suitable for this class of steels. An improvement of the failure prediction can be obtained by using damage mechanics. Therefore, an exact knowledge of the material-specific damage is essential for the application of various damage models. In this paper the results of microstructure analysis of a dual-phase steel and a complex-phase steel with a tensile strength of 1000 MPa are shown comparatively at various stress conditions. The objective is to characterize the basic damage mechanisms and based on this to assess the crack sensitivity of both steels. First a structural analysis with regard to non-metallic inclusions, the microstructural morphology, phase identification and the difference in microhardness between the structural phases is carried out. Subsequently, the development of the microstructure at different stress states between uniaxial and biaxial tension is examined. The damage behavior is characterized and quantified by the increase in void density, void size and the quantity of voids. The dominant damage mechanism of the dual-phase steel is the void initiation at phase boundaries, within harder structural phases and at inclusions. In contrast the complex-phase steel shows a significant growth of a smaller amount of voids which initiate only at inclusions. To quantify the damage tolerance and the susceptibility of cracking the criterion of the fracture forming limit line (FFL) is used. The respective statements are supported by results of investigations regarding the edge-crack sensitivity.

Methods for reducing weld porosity in argon-shielded arc welding of aluminium alloys

Cause analysis of porosity in aluminium argon-arc welded joints is carried out, particularly that of aluminium–lithium alloy 1424. Feasible production methods of reducing the quantity of voids in the joints are considered.

The Enhancement of the Resistance Window of TaN/GeTe/Cu Device by Controlling GeTe Film Structure

TaN/GeTe/Cu devices showed a switching behavior and a considerable increase in the on/off ratio due to GeTe microstructural changes. The Cu diffusion to the GeTe should be the origin of the switching behavior of the prepared devices, which indicates that the conductive bridging characteristics could be obtained even when using a pure GeTe solid electrolyte. The structural characterization suggested that voids are the main diffusion path of metallic bridges and that the electrical resistance of the on state is dependent on the quantity of voids in the GeTe film. We also found a method for controlling the quantity of voids in a solid electrolyte.

Effects of hydrogen on diffusion bonding of hydrogenated Ti6Al4V alloy containing 0.3 wt% hydrogen at fast heating rate

The diffusion bonding of hydrogenated Ti6Al4V alloy containing 0.3 wt% hydrogen was carried out. The effects of hydrogen on diffusion bonding at fast heating rate were investigated by SEM, EPMA, XRD, TEM and TG/DSC. According to the experimental observations, the featheriness α ′ martensite and β H phase disappeared after bonding, and the fine needle α ′ martensite and lamellar ( α + β ) structure were formed. Moreover, the FCC δ hydride translated into metastable hydride containing low hydrogen content with a crystal structure of TiH. Only the voids were observed in the interface, and the quantity of voids gradually decreased with the increase of bonding temperature, holding time and joining pressure. When bonded at 810 ∘ C for 8 min under a pressure of 6 MPa, the voids were closed and the room temperature shear strength of this joint reached 450 MPa. The fast heating prevented the most hydrogen escaping during rise in temperature, avoided the oxidation of joining surface and caused more phase transformation, which helped to improve the diffusion bonding quality.

A Preliminary Investigation of Tensile Properties of Glass-Mat Woven-Fabric-Reinforced Thermoplastic Elastomer Composites

Glass-mat woven-fabric-reinforced santoprene composites were fabricated at various temperatures and processing times. The molding temperatures were 190, 200, 210, 220 and 230'C, and the impregnation time was varied between 1 and 30 minutes. Samples were compression molded, and the effects of processing variables such as temperature and time on tensile properties were studied. The degree of impregnation of matrix resin into the reinforcing glass mat was characterized using scanning electron microscopy and tensile properties. In samples fabricated at 190'C, complete impregnation occurred before 10 minutes. The processing temperature had a pronounced effect on the composites; that is, degradation of the matrix resin occurred in samples fabricated at elevated temperatures. Evidence of degradation of the matrix resin processed above 190'C is confirmed by depression of the melting point of the matrix resin and reduction of the tensile strength. The tensile properties of the composites depend on the quantity of voids. Thus, the higher the void content, the lower the tensile properties.