The complexity of today’s products and materials is ever increasing. There is a demand on the industry to produce lighter, stronger, and more precise products. A common practice to achieve such products is to combine different materials to enhance strengths and reduce weaknesses; multi material products. Fabricating complex parts using multi materials does, however, lead to an increased difficulty in metrological verification and material characterisation. The use of computed tomography is today widespread within the industry, providing new possibilities for internal measurements, but there are still many uncertainties associated with the method. It is well known that large variations in density of multi materials greatly affects the contrast obtained by computed tomography, resulting in difficulties to scan and acquire reliable data from certain material setups.In this work the effects on internal measurements as a consequence of differences in X-ray penetration depth have been studied with regards to multi material setups. The main interest was the ability to acquire measurements from internal features of material compositions that are commonly used in the industry. In the result, difficulties and uncertainties associated with computed tomography of multi materials are highlighted and suggestions on how to reduce problems and obtain a more reliable test method are discussed.

Computed tomography is increasingly adopted by industries for metrological and material evaluation. The technology enables new measurement possibilities, while also challenging old measurement methods in their established territories. There are, however, uncertainties related with the computed tomography method. Investigation of multi-material components with, in particular, varying material thickness can result in unreliable measurements. In this paper the effects of multi-materials, and differing material thickness, on computed tomography measurement consistency has been studied. The aim of the study was to identify measurement inconsistencies and attempt to correct these with a dual-energy computed tomography approach. In this pursuit, a multi-material phantom was developed, containing reliable measurement points and custom-ability with regards to material combinations. A dual-energy method was developed and implemented using sequential acquisition and pre-reconstruction fusing of projections. It was found that measurements made on the multi-material phantom with a single computed tomography scan were highly inconsistent. It was also found that the dual-energy approach was able to reduce the measurement inconsistencies. However, more work is required with the automation of the dual-energy approach presented in this paper since it is highly operator dependant.

Industrial computed tomography of multi-material objects can be problematic due to difficulties in optimising the x-ray spectra of the scan. A possible solution to the problem is to use two x-ray spectra when scanning objects. The results from such scans can be fused into a single data-set that contains enhanced information. This practice is known as dual-energy computed tomography (DECT). In this work, the aim was to investigate two DECT methods ability to improve measurements in multi-material phantoms. To determine the performance of the methods three different phantoms containing precision spheres as measurement objects were investigated. To improve measurements in this work was defined as improving the measurement consistency of diameter measurements. The phantoms were also scanned with a single setting for comparison. The fusion of the data-sets was done using two methods, a linear fusion, and a novel non-linear fusion. Both of the methods relies on pre-reconstruction fusion of data-sets. The results show that both of the DECT methods improved measurement results significantly compared to the reference method. Further, the results show that the novel non-linear DECT method produces more accurate measurement results compared to the linear method.

X-ray computed tomography is a highly versatile investigation method with applications in a wide range ofareas. One of the areas where the technique has seen an increased usage, and an increased interest from industry,is in dimensional metrology. X-ray computed tomography enables the measurement of features and dimensionsthat are difficult to inspect using other methods. However, there are issues with the method when it comes tomeasurements of objects that consist of several materials. In particular, it is difficult to obtain accurate computedtomography results for all materials when the attenuation of materials differs significantly. The aim of this workwas to measure small air gaps between different materials using dual-energy X-ray computed tomography. Thedual-energy method employed in this work uses two energy spectra and fuses the data in the projections spaceusing non-linear fusion. The results from this study show that the dual-energy method used in this work was ableto capture more measurements than regular absorption computed tomography in the case of specimens withhighly different attenuation, enabling, in particular, the measurement of smaller gaps. The contrast-to-noise ratiowas also increased significantly with the use of dual-energy.

Joining of dissimilar materials is a topic of high interest for the industry. The ability to seamlessly join materials with significant differences in properties would advance the development of efficient designs and concepts within many fields. In this work, bonds between aluminium and carbon-fibre reinforced plastic have been studied. The aluminium side of the bonds were fabricated using classical methods (milling) and additive manufacturing. Two types of bonds were fabricated using additive manufacturing, one flat, relying on the rough surface for adhesion in the bond, and the other with surface features designed to hook into the carbon-fibre plies. All the bonds were fabricated using wet layup of carbon-fibre, the idea was that the aluminium parts would bond to the plastic composite in one step. The bonds were characterised using dual-energy computed tomography. The method used in this work was non-linear and based around fusing of projections acquired with different energy spectra. The mechanical strength of the bonds was also evaluated, both through tensile tests and four-point bending.It was found that the bonds including additive manufactured aluminium was stronger than the milled samples in general. In the computed tomography data, it could be seen that the adhesion in those bonds were better, most likely due to the rough surface. The strongest bonds were those with additive manufacturing surface features. However, the computed tomography data revealed that these bonds have difficulties with integration between the surface features and the carbon-fibre plies.

In this work, aluminium–carbon-fibre reinforced plastic joints have been studied. Three types of samples were designed as double lap joints where the aluminium inserts were fabricated using both classical methods (milling) and additive manufacturing. Two versions of the joint were fabricated using additive manufacturing, one flat, and the other with small teeth designed to hook into the carbon-fibre plies. The joints were characterised using a non-linear, dual-energy computed tomography method to evaluate the bond between the composite and the metal inserts. The mechanical strength of the bonds was evaluated, both through tensile tests and four-point bending. A simple finite element model was used to discuss the joints behaviour. It was found that the joints fabricated using additive manufactured inserts were more resistant to peel stress than the milled inserts. In four-point bending tests the moment that the joint could withstand was increased by roughly 300% with the use of additive manufacturing and 400% with the use of additive manufacturing and small teeth. However, in tensile tests it was found that the teeth design reduced the maximum load capacity of the joints by roughly 30% due to porosity. Further, it was found that the additive manufactured samples did not add to the capability of withstanding shearstress. The information gained with the dual-energy computed tomography method was highly valuable as the behaviour of the joints would have been difficult to explain without the porosity information.

The use of additive manufacturing is growing rapidly among industries within many different fields of fabrication. The benefits of applying additive manufacturing can be many and an application that have received special interest is the ability to design lightweight components. Lightweight components can be fabricated with additive manufacturing with the use of lattices that have a high stiffness to weight ratio and topology optimised, complex, designs. The most commonly used lattices today are based on trusses, however, there is also the possibility to generate lattices based around continuous surfaces. In this study, the properties of the popular body-centred-cubic lattice are compared the properties of the lesser known Schwartz diamond surface lattice. The mechanical compression properties, the fabrication processes, and the possibilities of the lattices are discussed and analysed.

In this work the effects of fabrication errors in the Body Centered Cubic strut lattice, and the periodic surface lattice Schwarz Diamond has been investigated. The lattices were both fabricated as-is and with induced errors to evaluate the lattices response to fabrication errors. The behaviour of the lattices were studied using compression test and in-situ computed tomography investigation. The results show that the Schwarz Diamond lattices in general are stronger than the Body Centered Cubic lattices in all of the measured aspects. Often up to five times stronger. It was also found that the elastic behaviour of the Schwarz Diamond lattices were mainly unaffected by fabrication errors while the Body Centered Cubic lattices experienced severe losses in performance. The behaviour of the lattices under compression could be followed using computed tomography which aided in the understanding of their behaviour.