Micro-computed Tomography Techniques Research Articles

Experimental investigation on the double-position impact responses and damage mechanism for Z-pinned composite laminates

Z-pins can enhance the resistance to delamination for composites effectively under impact loads. In this paper, the effect of Z-pinning technique on double-position low velocity impact behaviors for composite laminates were explored. The two impact positions had the same distance from the center of the laminates with the impact distances of 0 mm, 10 mm, 20 mm and 40 mm in between. The two positions were sequentially impacted with 5 J, 10 J and 20 J impact energy, respectively. The mechanical curves and the delamination damage projected area (DDPA) were recorded during the impact tests. Afterwards, scanning electron microscope (SEM) and X-ray micro-computed tomography (μCT) techniques were performed for characterizing the damage statuses and internal defects. Experimental results demonstrated that Z-pinning was unable to delay the delamination initiation at low impact energy, which led the similar damage statuses of double impact positions by comparing to the unpinned laminates. But at high impact energy, Z-pinning could suppress the delamination damage and internal defects, which weakened the damage interference. In addition, at high impact energy, dominated fiber breakage damage mode occurred for the second impact at the impact distance of 0 mm, accompanied by larger overlapped delamination area with the first impact and lower proportion of internal defects. This resulted in similar values of maximum central displacement and peak energy moment between the unpinned and Z-pinned laminates.

Effect of bias yarn on tensile fracture mechanism of multiaxial 3D angle-interlock woven composites

A novel 3D woven structure was designed and developed in this paper, namely multiaxial 3D angle-interlock woven composites (MAWC). In order to determine the specific influence of bias yarns on the tensile properties and failure mechanisms, two MAWCs with different weave patterns and 3D angle-interlock woven composites (3DAWC) were fabricated. Based on the meso-structure characteristics of MAWC, a realistic meso-model was proposed. The tensile behavior of MAWCs and 3DAWC were experimentally characterized, and the full-field strain distributions were recorded by digital image correlation (DIC). Moreover, a progressive damage model along with the X-ray micro-computed tomography (Micro-CT) technique were applied to reveal the damage processes and failure mechanisms of composites. Results showed that the axial tensile strength of MAWCs decreased due to the change of yarn orientation. The stress-strain curves of two MAWCs presented nonlinear behavior, while those of 3DAWC could be seen as linear within the whole strain range. Stress concentration regions of two MAWCs were found to be distributed more dispersedly than those of 3DAWC. The local tow splitting, fiber slippage and interfacial debonding were the primary failure modes of bias yarn in MAWCs under tension.

Analyzing the microstructure of a fresh sorbet with X-ray micro-computed tomography: Sampling, acquisition, and image processing

Abstract X-ray micro-computed tomography and image processing techniques were used to analyze fresh frozen sorbets at the outlet of a batch freezer. Sorbets made from water and sucrose were visualized and their microstructure was quantified with a resolution of 9 μm. Sodium iodide was confirmed to enhance the contrast between the unfrozen water and ice in sorbets. A thermostated box was employed to keep the samples at frozen state and constant temperature (close to −6 °C) during imaging. A reproducible quantification of size distributions and volume fractions of ice crystals and air bubbles were obtained. Data concerning ice crystals were in agreement with cryo-SEM imaging. Ice crystals represented approximately 50%wt of the product and their mean size was about 60 μm whereas air bubbles represented about 6% of the volume. Finally, X-ray microtomography equipped with a thermostated box was found to be a particularly relevant technique for the analysis of the microstructure of frozen desserts.

Geometrical and Topological Analysis of Pore Space in Sandstones Based on X-ray Computed Tomography

The pore geometry and topology properties of pore space in rocks are significant for a better understanding of the complex hydrologic and elastic properties. However, geometry and topology information about the sandstone pore structures is not fully available. In this study, we obtained the topological and geometrical pore parameters from a representative elementary volume (REV) for fluid flow in sandstone samples. For comparison, eight types of sandstones with various porosities were studied based on the X-ray micro-computed tomography technique. In this study, the REV size was selected based on the parameters from the respective pore network models (PNM), not just the porosity. Our analysis indicates that despite different porosity, all the sandstone samples have highly triangular-shaped pores and a high degree of pore structural isotropy. The high porosity group sandstones exhibit wider ranges of pore sizes than the low porosity group sandstones. Compared to the high porosity group sandstones, the low porosity group sandstones samples showing a higher global aspect ratio, indicating some pores exist in the form of bottlenecks. The pore topological properties of different sandstones show a high dependence of the porosity. The high porosity group sandstones obtain large coordination numbers, large connectivity densities and low tortuosities. The results from this study will help better understand the complex pore structure and the fluid flow in sandstone.

Characterization and Analysis of Porosities in High Pressure Die Cast Aluminum by Using Metallography, X-Ray Radiography, and Micro-Computed Tomography.

Mechanical performance of cast aluminum alloys is strongly affected by the defects formed during solidification. For example, fractography studies of the fatigue specimens have shown that fatigue failure in aluminum castings containing defects is almost always initiated from defects, among which pores are most detrimental. However, elimination of these pores is neither always economically nor technically possible. This work characterizes defects in high pressure die cast aluminum alloy as an illustrative material, but the methods used can be applicable to other types of castings and defects. The defects were evaluated using metallography as well as micro-computed tomography techniques. The variability of defects between the specimens of two sizes as well as different porosity levels are studied statistically. The distributions of defects based on location within the specimens are also analyzed. Moreover, the maximum defect size within the specimens are estimated using extreme value statistics, which can be used as an input to fatigue life prediction models. Extreme value statistics is applied on both 2D and 3D defect data. The accuracy of each approach is verified by comparing the estimated maximum defect size within the specimens with the maximum observed defects on fracture surfaces of fatigue specimens.

The role of particle shape on hydraulic conductivity of granular soils captured through Kozeny–Carman approach

Previous studies indicate that particle shape plays an important role in the hydraulic conductivity (k) of granular materials, often represented through the Kozeny–Carman (KC) concept. Several recent studies have improved the accuracy of the KC approach using the particle-size distribution (PSD) to estimate the specific surface area of particles but overly simplifying the effect of particle shape. This current study innovatively adopts the micro-computed tomography technique to compute particle shape parameters of different granular materials (e.g. glass beads, sand and crushed gravel) and then incorporate these parameters into the KC equation to estimate k more accurately, which is then validated with experimental data. The results indicate that k varies significantly according to different particle shapes even if the same mean porosity and PSD are retained. Particles that are less spherical and rounded have a larger fluid–particle contact area (i.e. larger shape factor), hence a smaller hydraulic conductivity. The study suggests a shape factor of 1·28–1·52 for natural sand and 1·84–2·1 for crushed sand and gravel can be used for KC method to estimate k while a porosity-dependent equation is proposed to estimate the tortuosity for different shaped materials.

Temperature-induced deformational responses and microstructural alteration of sandstone

The high-temperature response of rock is quite useful for successful exploration and exploitation of various conventional as well as unconventional energy systems such as underground coal gasification, and geothermal energy, where the associated rocks are exposed to various temperature and pressure conditions. In this study, we have investigated the effect of temperature and thermal alteration of an Indian sandstone. An investigation using acoustic emission, digital image correlation through ARAMIS, micro-computed tomography (CT) techniques and thermogravimetric analysis was performed to study the mechanical responses of the sandstone with increasing temperatures. The results indicate that uniaxial compressive strength (UCS), tensile strength and elastic modulus of sandstone reduced significantly and aligned in an overall decreasing trend with increasing temperatures. The maximum and minimum UCS of sandstone were obtained at 400 °C and 700 °C, respectively. Acoustic emission (AE) responses of the sandstone indicated an early crack initiation and crack damage for high-temperature treated specimens. The deformation was further analysed using the ARAMIS digital image correlation technique, and strain levels were visually quantified that exhibited a widespread distribution of higher strain for thermally-treated specimens at 700 °C. Microstructural thermal damage and different pore-characteristics were studied using micro-CT techniques that provided valuable information about the connected and non-connected pores of the sandstone and their evolution with increasing temperatures. The outcomes suggest a heat-induced increment in porosity by nearly 40 percent upon heating the samples from 25 °C to 600 °C, which can be attributed due to the opening of new cracks that stimulated structural damage.

High temperature fatigue of carbon/polyimide 8-harness satin woven composites. Part I: Digital Image Correlation and Micro-Computed Tomography damage characterization

This paper focuses on the experimental high temperature fatigue of Carbon/polyimide 8-harness satin woven composite materials. Traction-traction (R = 0.1) fatigue tests at 250 °C are carried out on Carbon/polyimide [45]6 8-harness satin woven composites under three different environments (air, 2 bar N2, 2 bar O2). Part I is specifically devoted to image based damage characterization by employment of Digital Image Correlation (DIC) and Micro-Computed Tomography (µ-CT) techniques. For the used samples, intra tow matrix cracks along fibres on the external plies are the first damage form at the ply-scale. Damage evolution on the sample surface can be followed during the test (in situ) by using 2D DIC. Moreover, fatigue tests are periodically interrupted to perform µ-CT scans to characterize and quantify the damage in the volume of the samples. The obtained results prove that the damage assessment methods presented in this work are suitable for environmentally-assisted fatigue tests on composite materials.

Effect of off-axis angle on low-velocity impact and compression after impact damage mechanisms of 3D woven composites

This paper presents the influence of the off-axis angles on the low-velocity impact (LVI) and compression after impact (CAI) damage mechanism of three-dimensional (3D) woven carbon/epoxy composites. Three kind of samples with different angles, 0°, 30° and 45°, of the weft and warp yarn orientation were experimentally tested using the drop weight LVI and quasi-static CAI equipment. X-ray micro-computed tomography (Micro-CT) techniques were used to identify the impact damage volumes, damage distribution and damage modes of 3D woven composites. Results indicated that the off-axis angles have significant effects on the LVI and CAI mechanical behavior and final failure mechanisms. Furthermore, Micro-CT revealed that off-axis samples exhibit more damage volumes and out-of-plane deformation. More importantly, the ultimate CAI strength of all the samples are largely governed by the global buckling. However, the formation of buckling damage in 0° samples runs from one edge of the specimen to the other side, whereas that in 30° and 45° samples mainly occur along the weft direction.

The retreatment abilities of ProTaper Next and F6 Skytaper: a micro-computed tomography study.

The aim of this study was to evaluate the retreatment abilities of the ProTaper Next (PTN) and F6 SkyTaper (F6) systems by using micro-computed tomography (microct), radiographic and microscopic imaging techniques. The root canals of twenty-six extracted mandibular premolar teeth were prepared and obturated. For the retreatment procedure, the teeth were randomly divided into two equal groups according to endodontic instruments: PTN (X4) and F6 (#40/.06). Pre- and post-operative filling material volumes were measured with micro-ct, and areas were measured with radiographic and microscopic imaging techniques. The percentages of residual material were calculated, and then statistically compared. The significance level was set at p<0.05. There was no statistically significant difference between F6 and PTN for retreatment efficacy in the micro-ct and radiographic imaging techniques (p>0.05). PTN demonstrated better cleaning ability when evaluated by microscopic imaging. (p<0.05). The correlation was moderate between micro-ct and radiographic, and micro-ct and microscopic imaging groups; however, it was strong between radiographic and microscopic imaging methods. The PTN and F6 files had similar effects in the removal of filling material with microct evaluation. The radiographic imaging method gave similar results with micro-ct imaging.

Investigation of hole quality in drilled Ti/CFRP/Ti laminates using CO2 laser

The machinability of titanium (Ti) and carbon fiber reinforced plastic (CFRP) (Ti/CFRP/Ti) laminates using CO2 laser is presented in this work. The effect of line energy and laser frequency on output responses such as heat affected zone (HAZ), taper angle (TA), metal composite interface (MCI) damage, surface roughness, dross height, and circularity were investigated. Line energy - the most influential parameter - demonstrated a threshold behavior; no drilling was observed below a certain line energy. Scanning acoustic microscopy (SAM), scanning electron microscopy (SEM), micro-computed tomography (μ-CT), and other imaging techniques were used to establish a correlation between laser parameters and CO2 laser machined damage in Ti/CFRP/Ti laminates. The results show that using a higher frequency and lower line energy can significantly improve the hole quality. However, dross free holes with minimum taper can be obtained using higher line energy.

3D pore structure characterization and hardness in a powder bed fusion-processed fully amorphous Zr-based bulk metallic glass

Recently, fabrication of bulk metallic glasses (BMGs) components with complex shapes has been realized using laser powder bed fusion (PBF). Initial defects such as porosity inherent to the PBF process can significantly degrade the mechanical integrity of the BMGs components. In spite of intensive studies on pore structures in 3D-printed crystalline alloys, pore structures in 3D-printed fully amorphous BMGs have not been characterized due to the difficulties in achieving large-scale fully amorphous structures. In the present work, the pore characteristics of PBF-processed fully amorphous Zr-based BMGs were systematically studied. The amorphous structure of the printed parts was first verified using X-ray diffraction (XRD). A non-destructive high-resolution X-ray micro-computed tomography (micro-CT) technique was then applied to evaluate the inner 3D pore structure, while microstructures below the resolution of X-ray micro-CT were examined in 2D using scanning electron microscopy (SEM). The printed amorphous parts can reach a total volumetric porosity as small as 0.45%. The distribution of pore size and pore sphericity were evaluated for the PBF-processed BMGs samples with different porosities, where two observed pore features were irregular large lack-of-fusion pores, and smaller gas-induced round pores. Furthermore, correlations were found between porosity, pore size and morphology. Finally, hardness tests at various loads revealed that while the intrinsic properties were constant irrespective of laser processing, the overall mechanical properties of the PBF-processed BMGs samples are dominated by pore characteristics. While the densest printed BMG sample had a comparable macroscale hardness to the as-cast material, an increase in porosity of ~8% led to a decrease in HV5 hardness of ~17%. The presented results provide a detailed analysis of pore characteristics, and their impact on mechanical properties of PBF-processed BMGs, for further experimental and computational studies of structure-property relationships in this materials class.

Cementitious material reinforced by carbon nanotube-Nylon 66 hybrid nanofibers: Mechanical strength and microstructure analysis

In this study, carbon nanotube (CNT) reinforced Nylon 66 nanofibers were used to modify the mechanical properties of cementitious materials. Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were dispersed into the polymer solution of Nylon 66. CNT reinforced Nylon 66 nanofibers were fabricated and mixed directly with ordinary Portland cement through an electrospinning process using an improved collector. Scanning electron microscope (SEM) and field emission transmission electron microscope (FE-TEM) were employed to investigate the morphological characteristics of nanofibers as well as the performance of nanofibers in the microstructure of hardened cement pastes. Moreover, the existence of CNTs in the hardened cement pastes was clarified by means of micro-computed tomography (CT) technique and thermal gravimetric analysis (TGA) method. The observations from mechanical strength tests showed the increase in toughness by 49 %, 30 % and 12 % as well as the increase in the tensile strength by 28 %, 43 % and 57 % in that order when adding Nylon 66 nanofibers, SWCNT reinforced Nylon 66 nanofibers and MWCNT reinforced Nylon 66 nanofibers into cement pastes.

Fatigue strength prediction of laser powder bed fusion processed Inconel 625 specimens with intentionally-seeded porosity: Feasibility study

Inconel 625 fatigue testing specimens with different levels of intentionally-seeded porosity in their gauge section (≤0.1, 0.3, 0.9 and 2.7%) were manufactured by laser powder bed fusion and subjected to stress relief annealing. The morphology, number and distribution of seeded defects were characterized using the micro-computed tomography technique. The effect of the different levels of porosity on the high cycle fatigue behavior of these specimens was studied using room temperature force-controlled fatigue testing according to the ASTM E466 standard (frequency of 30 Hz; R = 0.1) with a runout at 107 cycles. The fatigue strength of specimens with the lowest level of porosity (≤0.1%) was found to be 590 MPa. Next, using El-Haddad’s formulation of the Kitagawa-Takahashi model defining the limiting conditions for fatigue failure in the presence of defects and Murakami’s parameter for defect size rating, the fatigue strengths of specimens with 0.3, 0.9 and 2.7% porosity were predicted at 280, 190 and 160 MPa, respectively. The predicted values were found to deviate by less than 8% from the experimental results, which were, respectively, 288, 207 and 170 MPa.

3D sponges of chemically functionalized chitosan for potential environmental pollution remediation: biosorbents for anionic dye adsorption and ‘antibiotic-free’ antibacterial activity

ABSTRACT In this work, it was developed three-dimensional (3D) porous hydrogel sponges produced by the freeze-dried process using chitosan polymer functionalized by 11-mercaptoundecanoic acid (MUA). These chitosan-based sponges were used as cationic adsorbents for the removal of anionic methyl orange (MO) dye, simulating a model organic pollutant in aqueous medium. Moreover, these porous 3D constructs were also evaluated as ‘antibiotic-free’ antibacterial materials against gram-negative and gram-positive bacteria, Pseudomonas aeruginosa and Staphylococcus aureus, respectively, which were used as model pathogens possibly found in contaminated hospital discharges. These 3D hydrogels were comprehensively characterized through morphological methods such as scanning electron microscopy and X-ray micro-computed tomography techniques, combined with FTIR, Raman, and UV-visible spectroscopy analyses. Additionally, the surface area, the degree of swelling, and the adsorption profiles and kinetics of these scaffolds were systematically investigated. The chemically thiolated chitosan (CHI-MUA) hydrogels were successfully produced with a supramolecular polymeric network based on hydrogen bonds, disulfide bonds, and hydrophobic interactions that resulted in higher stability in aqueous medium than hydrogels of pristine chitosan. CHI-MUA exhibited sponge-like three-dimensional structures, with highly interconnected and hierarchical pore size distribution with high porosity and surface area. These architectural aspects of the 3D sponges favoured the high adsorption capacity for MO dye (∼388 mg.g−1) in water with removal efficiency greater than 90% for MO solutions (from 20 mg.L−1–1200 mg.L−1). The adsorption data followed a pseudo-second-order kinetic model and adsorption isotherm analysis and spectroscopy studies suggested a multilayer behaviour with coexistence of adsorbent-adsorbate and adsorbate-adsorbate interactions. Additionally, the in vitro evaluation of toxicity (MTT and LIVE-DEAD® assays) of 3D-sponges revealed a non-toxic response and preliminary suitability for bio-related applications. Importantly, the 3D-sponges composed of chitosan-thiolated derivative proved high antibacterial activity, specificity against P. aeruginosa (model hazardous pathogen), equivalent to conventional antibiotic drugs, while no lethality against S. aureus (reference commensal bacteria) was observed.

New Insights Into 3-Dimensional Anatomy of the Facial Mimetic Muscles Related to the Nasolabial Fold: An Iodine Staining Technique Based on Micro-Computed Tomography.

This study aimed to introduce a novel approach to study the facial mimetic muscles (FMMs) related to the nasolabial fold (NLF) and realize the visualization of complex 3-dimensional (3D) structures of the FMM. Micro-computed tomography (micro-CT) and iodine staining technique were used to obtain the 2-dimensional radiographs of the FMM. Materialise Mimics software was then used to reconstruct the 3D model of the FMM. The zygomaticus major muscle was not directly connected to the orbicularis oris muscle (OOM). The terminal fibers of the zygomaticus major muscle were located in the levator anguli oris. The surface of the FMM was covered with some unknown muscle fibers in the NLF. The terminal fibers of the zygolabialis ended in the middle of the ipsilateral OOM rather than the edge of the OOM. At the same anatomical level, the FMM fibers were so closely connected to each other that they were not separated by adipose tissue. A detailed 3D sequence of the muscle fibers in the modiolus at the corner of the mouth was determined. The muscle fibers in the modiolus were organized rather than disorganized. The terminal fibers of the levator anguli oris were located at the terminal fibers of the musculus depressor anguli oris at the corner of mouth. Although the micro-CT had many disadvantages, the micro-CT combined with iodine staining technique enabled the 3D anatomical study of the FMM related to NLF. We imported the 2-dimensional images obtained by micro-CT scanning into Mimics software, successfully reconstructed the FMM related to the NLF, and finally obtained images of complex 3D structures of the FMM related to the NLF. The shapes, positions, and 3D spatial relationships between the FMM related to the NLF were clearly visualized. The novel insights into the 3D anatomy of the FMM related to NLF may help understand the formation of the NLF. Finally, the results of this study may help improve rejuvenation surgery of the NLF in the near future.

Effects of Filler Distribution on Magnetorheological Silicon-Based Composites.

The smart materials subclass of magnetorheological elastomer (MRE) composites is presented in this work, which aimed to investigate the influence of filler distribution on surface morphology. Iron particles with sizes ranging from 20 to 150 µm were incorporated into the elastomer matrix and a 30% volume fraction (V%) was chosen as the optimal quantity for the filler amount in the elastomer composite. The surface morphology of MRE composites was examined by 3D micro-computed tomography (µCT) and scanning electron microscopy (SEM) techniques. Isotropic and anisotropic distributions of the iron particles were estimated in the magnetorheological elastomer composites. The filler particle distribution at various heights of the MRE composites was examined. The isotropic distribution of filler particles was observed without any influence from the magnetic field during sample preparation. The anisotropic arrangement of iron fillers within the MRE composites was observed in the presence of a magnetic field during fabrication. It was shown that the linear arrangement of the iron particle chain induced magnetization within the composite. Simulation analysis was also performed to predict the particle distribution of magnetization in the MREs and make a comparison with the experimental observations.

Simulations on the micro-seepage rules of gas and water based on micro-CT/CFD and the related contrastive analysis

This study first employed micro-computed tomography technique for scanning the gas-fat coal sample; then, using Avizo software, coal’s micro-pore structure model was established; finally, seepage behaviors of gas and water in the coal under a pressure of 3 MPa were simulated. Through comparison, it can be concluded that both gas pressure and water pressure decreased gradually along the seepage direction; at a same seepage length, water’s maximum seepage pressure significantly exceeded that of gas; gas’s velocity flow lines were overall fuller than water’s flow lines; using a same pore model, gas’s migration velocity far exceeded that of water; In terms of mass flow rate, water exceeded gas. The effluent mass flow rate at the outlet was smaller than the influent mass flow rate at the inlet. Overall, with the increase in the seepage length, gas and water’s mean seepage pressures and mass flow rates all decreased gradually, while their mean seepage velocities fluctuated greatly. Since the pores at the different coal cross-sections were developed to different degrees, the heterogeneity of the coal structure meant that the cross-sectional area of the pore channel varied irregularly along the seepage direction. The fitting curve can be reduced to three classes: logistic linear regression curve, Boltzmann function curve, Exp Dec curve, or poly curve.

Damage investigation and assessment due to low-velocity impact on flax/glass hybrid composite plates

There is limited information available in the body of knowledge regarding to the low velocity impact damage characteristics of sustainable bio-based such as flax fibre reinforced composites. This paper presents the results of full investigation of impact damage mechanisms on flax/vinyl ester laminated composite and flax-glass/vinyl ester hybrid composite laminates caused by low-velocity impact using a drop weight impact machine. The specimens were subjected to incident energy levels of 25 J and 50 J, in order to achieve a damage up to perforation and complete penetration. A 3D Finite Element Analysis (FEA) model was also developed using Hashin failure criteria. The damage and the predicted delaminations were compared using a high-resolution micro-Computed Tomography (μ-CT) technique. The results of the numerical analysis correlated well with the experiments and the imaging, which provided a full verification of the exact position of delaminations due to impact within the composite laminates.

Does the Misfit Volume of Prosthetic Crowns Differ Before and After Ceramic Application? An In Vitro Radiographic Microtomography Analysis.

To estimate the misfit volume of zirconia vs metal-ceramic crowns. Five specimens were fabricated from zirconia and five from nichrome (metal-ceramic). Microcomputed tomography techniques were used to obtain volumetric reconstructions of misfit volume before and after ceramic application. The mean misfit volume for metal-ceramic crowns was 8.80 mm3, and for zirconia crowns was 6.76 mm3 (P = .003, 95% confidence interval [CI] 0.714 to 3.358). Misfit volume also did not differ significantly before and after ceramic application (metal-ceramic, P = .375, 95% CI 0.513 to 1.363; zirconia, P = .253, 95% CI 0.257 to 0.977). Zirconia crowns had a smaller mean misfit volume than metal-ceramic crowns. The change in misfit volume after ceramic application was minimal and unlikely to be of clinical relevance.