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Mechanical properties of fibres reinforced composite materials depend on the type of fibres used, their percentage as well as their arrangement and orientation. As computer technology continues to improve, high-resolution computed tomography has proven to be an ideal instrument to analyse the structure of this kind of materials. In this context, various approaches have been proposed to detect the fibre orientation distribution and the relative degree of anisotropy of these composite materials. Some of these approaches are based on ‘individual’ measurements that isolate and reconstruct each single fibre and measure its properties. On the other hand, other approaches capture the characteristics of the fibre distribution by means of ‘global’ measurements computed on the entire set of tomographic data. The first methods are more precise but also more complex because they demand a procedure able to segment and separate each single fibre in the polymer, whereas the latter are easier to implement and can be applied even if fibre segmentation and separation is not effective or practicable. In this paper, a global method based on the technique called volume orientation – originally proposed several years ago to study the anisotropy of bone structures – is applied to fibre reinforced composite materials. This new approach does not require data acquired at very high resolution nor very complex procedures for individual segmentation of the fibres, but only binarised data through common thresholding procedures. The effectiveness of the proposed new approach is demonstrated by comparing it to the results obtained from a method based on individual measurements: when resolution and images quality are good enough, the volume orientation method gives results quite similar to the other approach. The analysis of three different case studies demonstrates its flexibility and its validity as an alternative to methods based on the separation of individual fibres, which are not always usable. The samples have been carefully selected in order to range between different attenuation contrast levels and also include a specimen subjected to mechanical testing which can be of great practical interest. Lay Description: Mechanical properties of fibres reinforced composite materials depend on the type of fibres used, their percentage as well as their arrangement and orientation. Today, both destructive and nondestructive techniques can be used in order to assess the fibre orientation. As computer technology continues to improve, high-resolution computed tomography has proven to be an ideal instrument to analyse the structure of this kind of materials, and then the fibre orientation distribution inside the material. In this context, various strategies have been proposed. Some of them require measurements that isolate and reconstruct each single fibre and measure its properties. On the other hand, other approaches capture the characteristics of the fibre distribution by means of ‘global’ measurements computed on the entire set of tomographic data. The first methods are more precise but also more complex because they demand a procedure able to detect and separate each single fibre in the polymer, whereas the latter are easier to implement and can be applied even if fibre segmentation and separation is not effective or practicable. In this paper, a global method based on the technique called volume orientation – originally proposed several years ago to study the microstructure of bone tissues – is applied to fibre reinforced composite materials. The aim of this work is to demonstrate that this new approach is easier to use. As a matter of fact, it does not require data acquired at very high resolution nor very complex procedures for individual segmentation of the fibres, but only binarised data through common thresholding procedures. The effectiveness of the proposed new approach is shown by comparing it to the results obtained from a method based on individual measurements: when spatial resolution and images quality are good enough, the volume orientation method gives results quite similar to the other already used approach. The analysis of three different case studies demonstrates its flexibility and its validity as an alternative to methods based on the separation of individual fibres, which are not always usable. The samples have been carefully selected in order to range between different attenuation contrast levels and different nature of the fibres (mineral, vegetable or synthetic). A specimen subjected to mechanical testing is also included, because of its great practical interest.

The aim of the current study is to propose a versatile, non-destructive inspection strategy to evaluate the structure of two different aircraft carbon fibre reinforced polymer (CFRP) -based composite configurations, which are widely used for structural elements, respectively layered composite and sandwich structure. X-ray computed tomography (CT) has been used as a flexible method for assessment of porosity levels in CFRP components in both types of configuration, permitting to investigate the volume distribution of the individuated pores/voids, giving an interactive 3D exploration and quantitative analysis of porosity by the complete 3D volume rendering of the analysed composites. Moreover, specific data analysis could supply detailed information on size, shape and position of pores or defect or misalignment which could be a valuable indication for damage tolerant design methodology or local stress analysis. This presented non-destructive approach based on CT can be a good alternative to standard destructive methods based on the acid digestion or 2D microscopy for porosity evaluation in composite, especially for severe stressed element in aerospace structure. Of course, the high resolution X-ray CT cannot substitute the ultrasounds test for analysing full scale components, but it can be complementary to it to provide accurate quantitative results on small samples used as references.

In many applications, polymeric foams (such as expanded polystyrene or expanded polypropylene) are used for protection from impacts. Standard design requires the foam to maximize the energy absorption, thus achieving large deformations (typically up to 25% and above in compression) while maintaining the stress level below a threshold value. In this work, steam chest-moulded EPS and EPP were characterized in relation to their density, microstructure and applied strain rate. Typical mechanical parameters (elastic moduli and plateau stress in compression) were compared with existing models and data in the literature. The strain-rate dependence was accurately described using Nagy’s phenomenological model. The mechanical behaviour of the foams was then correlated with their microstructure, as investigated using scanning electron microscopy and X-ray micro-tomography. Structural parameters were obtained using both (2D and 3D) techniques and relevant results were compared. © The Author(s) 2018.

The anisotropy of a short fiber reinforced composite produced by injection molding of basalt fibers and polypropylene matrix has been studied by X-ray microtomography (or micro-CT). Fiber orientation was analyzed using four stereological methods: Mean Intercept Length (MIL), Volume Orientation (VO), Star Volume Distribution (SVD) and Star Length Distribution (SLD). The fabric tensor obtained from micro-CT analysis provided information on the fiber orientation, indicating that fibers were partially aligned in the injection direction.

Cement composites containing recycled rubber add the advantage of a hydrophobic character to the typical benefits of a lightweight aggregate, and contribute to giving value to a relevant secondary raw material all over the world. In this work, we have tested these innovative construction composite materials in terms of water uptake by capillary rise, important cause of deterioration of masonries and building heritage at large. Moreover, we have investigated the potential of the X-ray-computed tomography in order to clarify the role played by rubber grains in affecting the air void system [dimension range: 10 µm−1 mm] of these porous materials, i.e. porosity, size distribution and localization of the pores within the cementitious matrix. This technique has been used also to gain information about the solid itself, i.e. on cement-rubber area distribution, as this parameter affects specifically the “bulk” surface energy (hence contact angle) of the composite. Results indicate that rubber-cement composites have higher porosity over the whole explored range, and more sensitively in the smallest detectable range [10 µm–100 µm]. Their lower permeation to water is ascribed to the assessed increase of the composite bulk water contact angle, and formally consistent with a lower mean radius of the pores.

Structural anisotropy of two-phase materials can be evaluated through global measurements, as volume orientation or mean-intercept length methods do, or through statistics performed on a set of individual measurements. This last procedure is encouraged by recent improvements in the spatial resolution of conventional X-ray tomography. In this paper, the above-described approaches were compared in three case studies: a foam subjected to an in situ compression test, a second foam with a completely different cell morphology and a plastic material reinforced with short fibres. The approach based on the subdivision into distinguishable objects of the considered material phase has proved to be more sensitive in highlighting small deformations in the structure or small irregularities in an otherwise isotropic structure. On the other hand, the other approach is more general and is always usable. The two methods for calculating the fabric tensor tend to converge as the average anisotropy of individual objects in the statistical population increases. The use of Lambert's cylindrical equal-area projection of cell/fibre directions or local volume orientations is suggested, because the density of points is preserved from the sphere to the plane surface. Finally, a quick vector method to evaluate the anisotropy of the directions distribution has been presented, by defining a coherence index of the average direction.

In fabrication of microelectronic devices two important steps are often recognized: i) all the processes performed on the wafer in order to build the active part of the devices and, ii) the assembly and packaging processes, typically performed on a chip, in order to fabricate interconnections between active part and exterior. The wafer back side is an active part of power devices and is normally coated with a stack of Ti-Ni-Au or Ti-Ni-Ag layers to ensure the best electrical contact with the frame on which the device is attached prior to the packaging. An important failure mechanism related to this particular process step is related to the diffusion of Ni to the surface of the stack that causes its oxidation on the back metal surface, inhibiting the correct connection to the metallic frame. Auger Electron Spectroscopy (AES) is a powerful analytical technique that can be used to detect this failure mechanism for its very high sensitivity in the characterization of surface layers. Unfortunately, its results are mainly qualitative. Quantitative extrapolations can be inaccurate using library Elemental Relative Sensitive Factor (ERSF) because they are mainly referred to a silicon substrate and could be not valid for a different matrix. A most accurate evaluation of the ERSF is based on the analysis, under identical experimental condition, of standard materials (with known concentration) that should be similar to the unknown sample and having the same matrix. However, the production of this kind of standard is not easy due to the mobility of Ni in Au and Ag. Another commonly used technique is the Energy Dispersive X-ray Spectrometry (EDS) which is less sensitive than the Auger and not sufficiently adequate for a quantitative analysis due to the limitation of the matrix correction methods. Recently, a new method to perform quantitative analysis by using Transmission Electron Microscopy (TEM) EDS was proposed, starting from bi-layers of pure elements. In this work we show how the use of TEM-EDS quantification of Ni in Ag could be a successful method for ERSF evaluation in order to overcome matrix effect in Auger quantification. For this purpose suitable foils of Ag/Al and Ni/Al were used. The validation of the method was performed on a sample with a tri-metal stack of Ti/Ni/Ag previously stimulated by means of a thermal budget to induce Ni migration on Ag surface. The quantitative analysis allowed us to use this characterized sample as AES standard for ERSF calculation. © 2018

This study is aimed at investigating the structure of a scaffold made of bovine gelatin and hydroxyapatite for bone tissue engineering purposes. In particular, the detailed characterization of such a material has a great relevance because of its application in the healing process of the osteochondral defect that consists of a damage of cartilage and injury of the adjacent subchondral bone, significantly compromising millions of patient's quality of life. Two different techniques exploiting X-ray radiation, with table-top setups, are used: microtomography (micro-CT) and microdiffraction. Micro-CT characterizes the microstructure in the three dimensions at the micrometer scale spatial resolution, whereas microdiffraction provides combined structural/morphological information at the atomic and nanoscale, in two dimensional microscopy images with a hundred micrometer spatial resolution. The combination of these two techniques allowed an appropriate structural characterization for the purpose of validating the engineering approach used for the realization of the hydroxyapatite gradient across the scaffold, with properties close to the natural model. © 2016 American Chemical Society.

Advanced polymeric foams with enhanced thermal insulation and mechanical properties are used in a wide range of industrial applications. The properties of a foam strongly depend upon its cell structure. Traditionally, their microstructure has been studied using 2D imaging systems based on optical or electron microscopy, with the obvious disadvantage that only the surface of the sample can be analysed. To overcome this shortcoming, the adoption of X-ray micro-tomography imaging is here suggested to allow for a complete 3D, non-destructive analysis of advanced polymeric foams. Unlike metallic foams, the resolution of the reconstructed structural features is hampered by the low contrast in the images due to weak X-ray absorption in the polymer. In this work an advanced methodology based on high-resolution and low-contrast techniques is used to perform quantitative analyses on both closed and open cells foams. Local structural features of individual cells such as equivalent diameter, sphericity, anisotropy and orientation are statistically evaluated. In addition, thickness and length of the struts are determined, underlining the key role played by the achieved resolution. In perspective, the quantitative description of these structural features will be used to evaluate the results of in situ mechanical and thermal test on foam samples. © 2016 Author(s).

Layered double hydroxides (LDH) are very used as fillers in polymer nanocomposites research. They cannot be used in their pristine form (magnesium and aluminum hydroxycarbonates) because they exhibit strong interlayer electrostatic interactions and tight basal spacings so that they require the intercalation of organic anions into clay galleries. The organic modification of LDH increases the filler-polymer compatibility, enlarges the basal spacing of the lamellae (making easier the insertion of the polymeric chains into the gallery), and promotes the exfoliation of the filler into the polymeric matrix. Organically modified LDH/polymer nanocomposites exhibit improved mechanical, thermal, and chemical properties when they are compared with pristine polymers or conventional composites. Moreover, the incorporation of LDH allows us to obtain materials with specific functionalities. For example, the intercalation of antimicrobial molecules into LDH (such as benzoate or stearate) and the use of the modified nanoparticles as fillers results in nanocomposites with antimicrobial activity. In this paper, several benzoate and/or stearate LDH/polypropylene (PP) nanocomposites have been produced for food packaging applications. The O2 permeability coefficient of the nanocomposite named 1.5% o-benzoate/1.5% o-stearate LDH/PP/3% PP-g-MAH reduces by 20% compared to unfilled PP and 30% compared to unfilled PP/3%PP-g-MAH. It is accepted that in such a nanocomposite, the lamellar structure of LDH creates a more tortuous path for the progress of oxygen molecules reducing the gas diffusion. For the novel nanocomposite material, the physical, morphological, mechanical, and gas barrier properties have been measured and the antimicrobial effect has been evaluated. In this paper, some benzoate LDH/polyurethane foam (PU) nanocomposites have been also produced. The filler dispersion into the PU has been investigated by scanning electronic microscopy. It was observed that organic LDH particles were uniformly dispersed into the walls of cells, forming small aggregates. The morphological properties of the foam have been analyzed by nanotomography. LDH/PU nanocomposite showed antibacterial and improved mechanical properties. © 2016 IEEE.

Advanced polymeric foams are used in a wide range of industrial and R&D applications. Their properties strongly depend upon the cell structure. Traditionally, their microstructure has been studied using optical or electron microscopy, limiting the investigations to sample's surface only. To overcome this shortcoming, the use of X-ray micro-tomography imaging is here adopted to allow for a complete 3D, non-destructive analysis of advanced polymeric foams. This work brings to fruition high resolution and low-contrast imaging techniques to perform quantitative analyses onto polymeric foams, where the low contrast of reconstructed structural features might hamper accurate quantitative analyses. Local structural features of individual cells are statistically evaluated, showing the key role of the achieved resolution. © 2016 Elsevier Ltd