Porosity Level Research Articles

Computational biomechanical analysis of Ti-6Al-4V porous bone plates for lower limb fractures

The current study investigates the biomechanical performance of porous bone plates augmented with three different cellular lattice structures, e.g., body-centered cube (BCC), simple cube (SC), and the superposition of simple and body-centered cube (SC-BCC) structures. The SC-BCC cellular structures, exhibiting improved torsional, compression, and bending stiffness, were strategically integrated into the bone plates. Configurations ranging from one to three rows, with porosity ranging from 30% to 90%. Increasing the number of rows and porosity maximized the interfragmentary movement at the fracture site. Specifically, SC-BCC configurations with one, two and three rows at 90% porosity demonstrated callus volume improvements of 31.33%, 42%, and 43.2%, respectively, compared with the lowest callus volume observed with SC-BCC at one row and 30% porosity. Regardless of the improved volume, callus stiffness was highest at 30% and 90% porosity levels across all cases, indicating more mature tissue formation in calluses and better physiological load support. High stresses located at 90% porosity, followed by 50% porosity, discouraged their mechanical performance. Therefore, employing 30% porosity configurations with appropriate vertical rows for desired movement is recommended for optimal biomechanical performance. However, 90% porosity may be suitable in scenarios involving minimal forces and restricted patient movement.

The effect of direct energy deposition arc mode on the porosity of AA5087 aluminum alloy

The paper evaluates the effect of the welding mode of the CMT-based direct energy deposition arc (DED-Arc) process on the porosity of AA5087 aluminum alloy walls. Three welding modes were used to produce the walls: cold metal transfer (CMT), CMT-Pulse (CMT-P), and CMT Cycle-Step (CMT-CS) with heat inputs of 128.5 J/mm, 150.4 J/mm, and 152 J/mm, respectively. Porosity was assessed with a light microscopy (LM) and computer tomography (CT). The wall produced with the lowest heat input had the lowest average porosity of 0.641 % compared to CMT-P (0.799 %) and CMT-CS (0.766 %). CT results followed the same trend with porosity of 0.21 %, 0.32 %, and 0.27 % for CMT, CMT-P, and CMT-CS, respectively. The porosity level strongly correlates with the hydrogen content. The lowest porosity (CMT) at the lowest hydrogen content (5.29 ppm) is associated with lower hydrogen solubility in a molten pool at lower heat inputs. Most of the detected pores in all modes ranged from 51 to 100 μm in size.

Effect of beam oscillation frequency on porosity in laser welding of aluminum alloy lap-butt joints

Many investigations into laser oscillations for mitigating severe porosity in aluminum alloys have involved trading off penetration depth, potentially disrupting the porosity suppression mechanism. In this study, an oscillation laser butt-lap welding technique was designed, and the effect of oscillation frequency on cross-section morphologies and porosity rate was investigated while maintaining the constant weld depth. The findings unveiled that heightened oscillation frequencies led to diminished porosity levels, and this pattern remained consistent, even in cases where weld depths were extended. High-frequency laser beam oscillation enhanced the stability of the keyhole, increased the duration of the molten pool existence, and reduced porosity to 0.17%. Thus, this study offered significant insights into the impact of oscillation on laser welding of aluminum alloys.

Pressure-less Ag-Sinter: Necking, Pores Structure and Its Properties

Pressure-less Ag-sinter die-attach structure revealed good-networked silver interconnects along with discontinuous shrinkage porosities. A thin sheet test sample is processed to be evaluated with commercially available test equipment. In this study, test samples are stencil printed to a thickness from 70 to 100 µm and sintered at 200/250°C for 30/60 minutes. A test sample to a thickness of 13mm is processed by stacking a few layers of printed Ag-sinter and sintered at 200°C for 1h. Interestingly, good necking is observed in between the silver powder particles and measured properties for three different porosity levels of pressure-less Ag-sinter are as follows: • Discontinuous porosities of structure are about 15 to 20%, 25 to 35% and 45 to 55% depending on the paste chemistry and formulation (with or without binder) *Density of these pores structure is fro 4.5 to 7.7 g/cc • Electrical sheet resistivity is from 3.7 to 9.2 µΩ.cm • Thermal conductivity is from 80 to 190 W/m°K • Elastic modulus (ultrasonic testing method) is from 7.2 to 38 GPa 1. Lower the porostiy, hight the thermal conductivity and elastic modulus • Coefficient of thermal expansion (CTE) is about 19.2 to 21.5ppm • Specific heat capacity (Cp) is about 0.24-0.25 J/Kg°K *Both CTE and Cp properties of Ag-sinter are not influenced by porosity in the structure

Fatigue performance of beta titanium alloy topological porous structures fabricated by laser powder bed fusion

The performance of porous β-titanium alloys is crucial for their diverse applications, with fatigue characteristics playing a pivotal role in shaping the design of these porous structures. While topological configurations have exhibited exceptional property, a systematic understanding of their fatigue performance is lacking in recent literature. This study reveals that at a porosity level of ∼75%, designed topologically optimized (TO) structures surpass rhombic dodecahedron (RD) structures in compressive yield strength by ∼4 times (149 ± 3 MPa vs. 38 ± 1 MPa). Furthermore, post-heat treatment further enhances the yield strength of TO structures by ∼15%, reaching 172 ± 3 MPa due to grain refinement and β phase stabilization. Moreover, the as-printed TO structure exhibits exceptional compressive fatigue endurance, enduring stress approximately ∼5 times higher than the as-printed RD structure at a cycle count of 106. Microstructure analysis after fatigue testing reveals a reduction in the α" martensitic phase and an increase in stress-induced ω phase in the heat-treated TO structure, contributing to a slight improvement in fatigue strength compared to the as-printed TO structure. The exceptional fatigue performance observed in LPBF-built beta-type titanium alloy within TO structures highlights the complex relationship between porous structure design, microstructure, compressive strength, and fatigue performance.

Effects of Porosity on CFRP Repair Performance with Aerospace Applications

On-site repairs of carbon fiber reinforced polymer composites, wet layup repairs with heat blanket method play a critical and practical role for the composite defects that occur in production and assembly. The porosity level should be controlled for the repair parts with heat blanket method since the pressure value, which enables ply consolidation, reduce the risk of delamination in the composite layers, is less or zero with the wet layup repaired parts with heat blanket compared to repair parts with autoclave pressure.
 In this experimental study, an investigation was conducted regarding the tensile strength change of prepreg structures using wet lay-up repair techniques with heat blanket based on the porosity, with a specific focus on stepped-repaired carbon fiber reinforced polymer laminates.
 This work aims to understand the strength and the associated failure mechanisms of on-site repaired woven carbon fiber reinforced polymer laminates through experiments. The Automatic Ultrasonic Pulse Echo Inspection Method was utilized to see whether porosity level of each repaired samples is within allowable design limits for this purpose. Prepreg structure's repairs using wet lay-up produced according to standardized aerospace procedures were tested under uniaxial tension per ASTM 3039D. The relationship between attenuation difference (ΔdB) and tensile fracture values has been explored, with a focus on investigating the associated failure mechanisms. Initially, a 60% strength recovery was observed for repairs with an 8-decibel difference. However, as the decibel difference increased, the strength recovery gradually decreased, ultimately reaching 45.2%.

A PEGylated PVDF Antifouling Membrane Prepared by Grafting of Methoxypolyethylene Glycol Acrylate in Gama-Irradiated Homogeneous Solution.

In this study, methoxypolyethylene glycol acrylate (mPEGA) served as a PEGylated monomer and was grafted onto polyvinylidene fluoride (PVDF) through homogeneous solution gamma irradiation. The grafting process was confirmed using several techniques, including infrared spectroscopy (FTIR), thermodynamic stability assessments, and rotational viscosity measurements. The degree of grafting (DG) was determined via the gravimetric method. By varying the monomer concentration, a range of DGs was achieved in the PVDF-g-mPEGA copolymers. Investigations into water contact angles and scanning electron microscopy (SEM) images indicated a direct correlation between increased hydrophilicity, membrane porosity, and higher DG levels in the PVDF-g-mPEGA membrane. Filtration tests demonstrated that enhanced DGs resulted in more permeable PVDF-g-mPEGA membranes, eliminating the need for pore-forming agents. Antifouling tests revealed that membranes with a lower DG maintained a high flux recovery rate, indicating that the innate properties of PVDF could be largely preserved.

Impact of filler and gelling catalyst/agent on properties of flexible polyurethane foam

AbstractIn this study, the physiomechanical properties of carboxymethylcellulose sodium salt (Na‐CMC salt) filler‐loaded foam and its impact on the wicking capacity of the foam were investigated in juxtaposition with the increasing tin concentration. According to the study's findings, standard unfilled foam demonstrated no wicking at all, while flexible PU foam filled with Na‐CMC salt, even with low porosity and subpar mechanical traits, displayed wicking heights of 4 mm, 3.4 mm, and 2.8 mm in test specimens of thicknesses of 6 mm, 8 mm, and 10 mm. Moreover, filled foam with a higher porosity level exhibited significantly better wicking heights of 11.4 mm, 10.8 mm, and 8.2 mm. The inclusion of CMC filler in the PU foam matrix is the reason for enhanced wicking property in foam. The sample thickness and wicking height trends are consistent among all foams; as foam sample thickness increases, wicking height progressively falls. The correlation between the foam's porosity value and the number of closed cell windows is confirmed by stereomicroscopy and the porosity values. According to this study, the infused filler's characteristics have a greater influence on the foam's wicking capacity than the foam's porosity. This study contributes significant insights into ongoing initiatives to enhance user experience, well‐being, and hygiene through innovative and meticulously designed new developed mattress foam using Na‐CMC as a filler.Highlights Co‐relation between concentration of tin and infused filler on wicking property. Standard unfilled foam demonstrated no wicking at all. Na‐CMC salt filled foam displayed wicking heights. After 15% increase in tin level, mechanical properties of foam degrade. Wicking depends on nature of infused filler and the foam's porosity.

Empirical investigation on controlled porosity level and dry sliding wear behavior of Al7075-(T6) doped with SiC+MoS2 based hybrid composites via advanced vacuum-assisted stir casting

This paper investigated Al-based hybrid metal matrix composites (HMMCs) comprised of Al7075-(T6) base metal matrix doped with SiC+MoS2 reinforced particles for high-strength, lightweight, and wear-resistant applications. Taguchi’s design of L9 orthogonal array (OA) with three process variables having different levels (such as SiC particle (2.5, 3.5, and 4.5 wt.%), MoS2 particle (1.5, 2.5, and 3.5 wt.%), and stirring speed (580, 600, and 620 rpm)) has been selected for fabrication of Al-based HMMCs via an advanced vacuum-assisted stir casting route. The controlled porosity level and dry sliding wear behavior (i.e. wear loss) of fabricated hybrid composites at an ambient temperature of 35°C have been conducted. Besides, metallographic evaluation was inspected through optical microscopy, high-resolution FESEM, and SEM-EDS techniques. Furthermore, experimental outcomes obtained from Taguchi’s design of experimentation were optimized by analysis of variance (ANOVA); and also validated through an artificial neural network (ANN) modeling with a network topology of 3-10-2. The results concluded that a homogeneous dispersion of reinforced particles over the base metal matrix (with controlled both abrasive and adhesive wear mechanisms of worn surfaces). Moreover, a significant reduction in porosity level (up to 29.41%) and wear loss (up to 4.94%) of the proposed hybrid specimen (S4) as compared with an unreinforced specimen (S0). In addition, the predicted values obtained from the ANN model were confirmed in close proximity to Taguchi’s experimental outcomes (with less percentage error), which in turn certified the authentication of the constructed ANN model for the Al-based HMMCs.

Pore Structure Characteristics of Shale Oil Reservoirs with Different Lithofacies and Their Effects on Mobility of Movable Fluids: A Case Study of the Chang 7 Member in the Ordos Basin, China

The Chang 7 member of the Triassic Yanchang Formation in the Ordos Basin is a significant continent shale oil reservoir in China. Therefore, conducting an in-depth investigation into the pore structure and fluid mobility characteristics of the Chang 7 shale oil reservoir holds immense importance for advancing shale oil exploration. This study conducts a detailed analysis of the pore structures and their impact on fluid mobility of the Chang 7 shale oil reservoir using multiple methodologies, i.e., a cast thin section, scanning electron microscopy (SEM), X-ray diffraction (XRD), high-pressure mercury injection (HPMI), low-temperature nitrogen adsorption (LTNA), and nuclear magnetic resonance (NMR). The results show that the sandstone in the Yanwumao area of the Chang 7 shale oil reservoir consists mainly of lithic arkose and feldspathic litharenite, which can be classified into three lithofacies (massive fine-grained sandstone (Sfm), silt-fine sandstone with graded bedding (Sfgb), and silt-fine sandstone with parallel bedding (Sfp)). Moreover, three pore structures (Type I, II, and III), and four pore spaces (nanopores, micropores, mesopores, and macropores) can be characterized. Pore structure Type I, characterized by large pores, exhibits bimodal pore diameter curves, resulting in the highest levels of movable fluid saturation (MFS) and movable fluid porosity (MFP). Pore structure Type II demonstrates unimodal pore structures, indicating robust connectivity, and higher MFS and MFP. Pore structure Type III primarily consists of dissolved and intercrystalline pores with smaller pore radii, a weaker pore configuration relationship, and the least fluid mobility. Furthermore, a correlation analysis suggests that the pore structure significantly impacts the fluid flowability in the reservoir. Favorable petrophysical properties and large pores enhance fluid flowability. Micropores and mesopores with high fractal dimensions have a greater impact on reservoir fluid mobility compared to macropores and nanopores. Mesopores mainly control MFS and MFP, while micropores govern the shift from bound fluid to movable fluid states. Among the lithofacies types, the Sfm lithofacies exhibit the highest fluid mobility due to their significant proportion of macropores and mesopores, whereas the Sfgb lithofacies have lower values because they contain an abundance of micropores. The Sfp lithofacies also dominate macropores and mesopores, resulting in medium fluid mobility levels. This study combines lithofacies types, micro-reservoir pore structure characteristics, and mobile fluid occurrence characteristics to better understand the dominant reservoir distribution characteristics of the Chang 7 shale oil reservoirs in the Ordos Basin and provide theoretical information for further optimization of production strategies.

Effect of Build Geometry and Porosity in Additively Manufactured CuCrZr

Abstract The current work presents an understanding of microstructure and mechanical properties as a function of build geometry and build orientation in Cu-Cr-Zr via the laser powder bed fusion (LPBF) technique. Porosity, microstructure, and mechanical properties have been compared in as-printed (AP) and heat-treated (HT) LPBF Cu-Cr-Zr, between cylindrical and cube geometries, along the longitudinal (L) and transverse (T) build orientations. Varying porosity levels were observed that yielded parts with 96–97% relative density in the AP condition. The AP microstructure demonstrated a hierarchical microstructure, comprising grains (2.5–100 μm) with a cellular substructure (400–850 nm) and intracellular nanoscale (20–60 nm) precipitates. Unlike most materials in the AP condition, crystallographic texture was found to be absent; however, very distinct river-like patterns highlighted a novel feature of the LPBF Cu-Cr-Zr. Upon solutionizing and aging, Cr precipitates were seen heterogeneously nucleating along cell boundaries (0.5–1.3 μm), causing up to 45% enhancement in the strength and a 4–5% lower ductility. The yield strength along the transverse orientation was 10–16% higher than that of longitudinal orientation, in both the AP and HT conditions. Fracture surface of the tensile samples exhibited micro-voids, cleavage facets, and unmelted particles. Despite the porosity, overall mechanical properties matched well with those obtained in nearly dense (>99%) samples and the mechanical property debit was less than 10%.

The Influence of Filling System Design on Quality Performance in Gray Iron

Significant evidence now supports the quality improvement seen in castings that employ naturally pressurized filling systems in their production. However, despite the documented evidence for improvement, these systems have not become ubiquitous. Gray iron, the industry’s most prominent alloy, has been particularly slow to accept the shift in system design. The suggested tolerability of gray iron to turbulence, the market’s price sensitivity, and the perceived economics of naturally pressurized systems are potential factors that have hindered adoption. However, if, through improved quality, the economic justification for these systems can be made in this adverse setting, there is a merit in their application to all alloys and processes. A sample gray iron part, currently being produced in a foundry environment with known porosity issues, was selected, to which a new system and several basin designs were applied. A mixed method analysis of casting simulations, production trials, and economic and environmental modeling was used to evaluate system performance. The results show a strong association between filling system design and sub-surface porosity. However, no association was found between basin design and porosity occurrence at lower porosity levels. Nevertheless, the economic and environmental modeling highlights that quality-orientated systems yield significant financial and environmental savings for the organization due to reduced scrap levels. These findings imply that quality-orientated system designs should be employed even when cost is the most critical measure.

Sound Absorption Characteristics of Unsaturated Porous Material Calculated by Modified Transfer Matrix Method

Porous materials have emerged as one of the most widely employed sound-absorbing materials in practical applications, owing to their excellent sound absorption properties and lightweight nature. Unsaturated porous materials have the potential to achieve superior sound absorption effects and significantly reduce mass. However, current research on the sound absorption performance of unsaturated porous materials is limited. This paper used a modified transfer matrix method (MTMM), which relies on matrix dimensionality reduction, to analyze the sound absorption characteristics of unsaturated porous materials under various boundary conditions. The study also examines the impact of different parameters, such as material thickness and saturation, on sound absorption performance and compares the results. The findings indicate that when a solid elastic plate is attached to an unsaturated porous elastic plate, the absorption coefficient decreases while the transmission loss increases. Additionally, reducing the thickness of the plate and increasing its porosity and saturation levels lead to an increase in the absorption coefficient and a decrease in the transmission loss.

Effects of porosity on ultrasonic attenuation coefficient, shear properties and failure mechanisms of CF/EP laminates

Carbon fiber reinforced epoxy composite (CF/EP) laminates with porosity ranged from 0% to 2.5% were prepared under inadequate curing pressures, and then applied to ultrasonic, metallographic and mechanical testings. Porosity was evaluated using an ultrasonic attenuation model, which was established by taking consideration of surface losses, material attenuation coefficient and void attenuation coefficient. Shear properties were determined via short beam shear (SBS) method and porosity-related failure mechanisms were characterized using ultrasonic B-Scan and metallographic analysis. The results show that there is a third-order polynomial correlation between porosity level and ultrasonic attenuation coefficient. The shear strength approximately drops by 15%, 30%, 40% and 45% with porosity level up to 1.0%, 1.5%, 2.0% and 2.5% respectively. The detrimental effects of Porosity can be attributed to the reduced bonding area between plies or among fiber-resin area as well as the crack initiation and propagation.

Methodology for the production of Ni-based open-cell metal foam using ultrasound-assisted electroplating

ABSTRACT Metal foam is a new type of metal that has a variety of uses because its properties can be customised to suit a specific need. Since it has the potential to replace traditional metals, it is important to explore the most advanced methods for creating foams with various levels of porosity. However, it is difficult to produce metal foam cost effectively while also achieving the desired properties due to the random structure and complexity of the process. Therefore, this manuscript outlines a step-by-step guide for creating Ni-based foam using electrodeposition, which overcomes these developmental challenges. Also, the manuscript discusses the characterisation of the foam’s integrity parameters at each stage, as well as the problems encountered during production and their solutions to optimise the developmental process. Finally, the manuscript presents mechanical testing results that demonstrate the foam’s compressive strength of 10.21 MPa at 80% length reduction, porosity of 92% and pressure drop through foam of 0.026% was reported. The developed foam can find usability in corrosive and high-temperature filtration systems, substantiated by mechanical testing results, that are also described.

The influence of hydrocarbon generation on the sealing capability of mudstone caprock rich in organic matter

To investigate the sealing capability of mudstone caprock during the evolution of organic matter (OM)-rich mudstone, a series of hydrous pyrolysis experiments were first conducted to examine the impact of hydrocarbon generation. The pore type, pore structure, porosity, and gas breakthrough pressure of pyrolytic residual samples were analyzed by field emission scanning electron microscopy, low pressure nitrogen adsorption measurements, porosimetry, and gas breakout core experiments. To model the environment at different depths, these six experiments on hydrous pyrolysis were performed at different temperatures, lithostatic pressures, and hydrodynamic pressures, while other experimental factors such as the original sample, heating time, and rate were kept constant. The results showed that during the thermal evolution process, hydrocarbons were generated from OM in mudstone, resulting in the formation of pores within the OM. Organic acids produced by hydrocarbon generation effectively dissolved minerals, leading to the creation of numerous dissolution pores. Changes in pore type led to changes in pore structure and porosity. The volume of micropores and macropores showed an increasing trend before reaching a Ro value of 1.41%. However, after passing this threshold, they began to decrease. The volume of mesopores showed a decreasing trend before reaching a Ro value of 1.32%. After 1.32%, they began to increase. The porosity was mainly affected by the pore volumes of the mesopores and macropores. The porosity exhibited two peaks: the first occurred at a Ro value of 0.72%, with a porosity level of 4.6%. The second occurred at a Ro value of 1.41% and a porosity level of 10.3%. The breakthrough pressure was a comprehensive reflection of these influences, and its trend exhibited a negative correlation with porosity (R2 = 0.886). For two high values of porosity, the breakthrough pressure corresponded to two low values. Smaller values of the breakthrough pressure indicated a poorer sealing capability of the mudstone caprock. Overall, hydrocarbon generation in the mudstone affected the sealing capability. The mudstone in the studied area exhibited good sealing at Ro below 1.32%. However, once above the 1.32% threshold, the fluctuations of the breakthrough pressure values exhibited considerable variability, requiring a comprehensive evaluation to assess its sealing capability.

Degradation of atmospheric plasma sprayed Gd4Al2O9 coating attacked by molten Na2SO4+V2O5 salt mixture at 700–950 °C

In this work, investigation on degradation of the APS Gd4Al2O9 as a new coating against the 50 wt% Na2SO4+50 wt% V2O5 molten salt mixture at 700oC–950 °C for 2 h and 10 h has been conducted. Results indicate that the as-sprayed Gd4Al2O9 coating exhibited outstanding corrosion resistances. Factors related to higher Gd3+ cation ratio, Gd2O3 as a stronger basic oxide than Al2O3, Gd–O with larger chemical bond length and lower bond energy were responsible for a rapid formation of a continuous GdVO4 corrosion layer at any temperature level and corrosion duration. Amorphous phase with much reduced chemical bond strengths in the as-sprayed Gd4Al2O9 coating leading to a significantly reduced apparent porosity level but rather increased corrosion reaction speed played an important role in consuming and solidifying the molten salt mixture as fast as possible.

Improvisation in wicking property of flexible polyurethane foams by adding bamboo and gelatin fillers

PU foam is one of the softest, most easily accessible, and affordable mattress materials. In PU foam, wider pores and a more open-cell structure have both advantages and drawbacks. Despite having fewer cells PU foam does not control airflow very effectively and commonly faces criticism for causing body heat and for retaining moisture. A warm, humid climate because of stored body moisture and sweat functions as a haven for bacteria and germs and encourages the proliferation of dust mites contributing to excessive odour and allergic reactions. This study aims to investigate the impact of bamboo and gelatin filler dosage or loading on the wicking property of the foam by using a discontinuous foaming process. Foams with gelatin and bamboo fillers were prepared at 2, 4, and 8% by weight concentrations, respectively, along with a standard 32-density foam without filler. A comparative study was conducted on the effect of increasing filler content on the wicking and mechanical properties of the foam. The wicking and porosity levels of bamboo-filled foam were higher than standard foam and gelatin-loaded foam. With increasing concentrations of bamboo filler, a rapid increase in foam wicking by 7–10 mm was noted. However, an increase in gelatin filler concentration resulted in an increase in foam porosity and elongation with a slight improvement in wicking ability. Improvisation in the wicking property of the foam was observed with dosage increment of bamboo filler. According to this research findings, the bamboo powder can be utilized as a filler to enhance wicking properties in flexible polyurethane foam.

Prediction of absorptivity in Multi-Jet Fusion manufactured polypropylene structures through laser flash and corrected porosity method

For the first time in the literature, this study validates the absorption phenomena in Multi-Jet Fusion (MJF) printed polypropylene (PP) structures through Laser Flash (LFA) and Corrected Porosity (CP) methods. The influence of process parameters such as build height and build orientation was investigated on tensile properties, crystallinity, porosity and thermophysical attributes in MJF printed PP coupons. Results showed that both crystallinity and tensile performance did not significantly vary with either location or build orientation. Interestingly, samples printed in the Z orientation showed a 35% decrease in strain, indicating that Z-oriented MJF coupons were more brittle than the flat samples (XY). Samples printed in Z orientation also possessed higher porosity and relatively lower crystallinity than the XY orientation. However, large deviations within porosity values were an obstacle to determining a suitable build chamber location for manufacturing dense samples. Therefore, a detailed investigation on porosity of printed samples using micro-CT scans and CT image analysis was necessary. Initially, poor contrast was obvious when MJF printed samples were positioned vertically in the micro-CT chamber which was mainly due to high value of horizontal intensity profile (HIP ~ 70%). Contrast in MJF samples improved significantly in the horizontal orientation (HIP ~ 40%). In parallel, the half-time and heat loss were measured in LFA to understand changes in absorption phenomena with height and orientation of the build. A direct correlation was found between LFA half-time and porosity only when the porosity correction method was implemented. Corrected porosity value was found to be inversely proportional to the heat loss of printed PP samples which indicated higher absorption for samples printed in the bottom of build chamber, XY12, whereas lower absorption was observed for less dense Z samples. Finally, heat loss phenomenon was verified using dense reference Pyroceram samples as they possess high diffusivity and low half-time and porosity compared to MJF printed samples. There is a science behind understanding the absorptivity of the MJF process which is related to the complexity of the process and is challenging to address in MJF PP samples when mixed with carbon black. The study showed that accurately determining the level of porosity is the key to validate absorption phenomena within MJF printed coupons. The contributions of this work are the investigation of the light absorption phenomena in MJF printed PP structures, and the establishment of the absorption-porosity correlation. These contributions help to predict the mechanical properties and subsequently the overall quality of the produced parts which can save cost and time in effectively utilising the MJF process.

SEM Image-based Porosity Analysis of Fire Damaged High Strength Concrete

The porosity of concrete affects the durability of reinforced concrete structures, wherein high levels of porosity are linked to a shorter service life. Recent works have noted that high porosity levels naturally exist in the aftermath of a fire exposure – especially when concrete is classified as high strength concrete (HSC). To shed more light into this phenomenon, this paper showcases a method for measuring the porosity of HSC under elevated temperatures through scanning electron microscopy (SEM). In this method, SEM-based images were examined to quantify the surface porosity of fire-affected HSC. Detailed image analysis was performed for HSC exposed to various heating durations. The study concludes that the surface porosity obtained via the SEM processing method is in good agreement with that from the SEM-based method (with a minor average difference of 3.8%). As such, the proposed method is expected to be reliable for the porosity analysis of fire-damaged concrete.