Observation of damage initiation for trans-laminar fracture using in situ fast synchrotron x-ray radiography and ex situ x-ray computed tomography

Trans-laminar fracture is an important topic for engineering composites. In this study, trans-laminar fracture initiation in quasi-isotropic carbon/epoxy laminates made of non-crimp fabrics was examined using in situ fast synchrotron X-ray radiography and ex situ X-ray computed tomography. The maximum split lengths were measured by in situ radiography and were compared with the predicted values in a detailed FE model using cohesive elements. Ex situ computed tomography scans were also conducted to confirm that no fibre breakage occurs before the final load drop in the experiments. In situ and ex situ observations are complementary for the understanding of damage initiation

Characterisation of ‘Braeburn’ browning disorder by means of X-ray micro-CT

Unfavourable gas conditions during controlled atmosphere storage may cause browning symptoms in ‘Braeburn’ apple fruit (‘Braeburn’ browning disorder or BBD). These symptoms are likely to reflect massive changes in the microstructure of the fruit tissue. In this study, individual cells, the internal air network and the 3-D distribution of pores inside ‘Braeburn’ apple tissue were examined using high resolution X-ray micro computed tomography. Different stages of BBD could be clearly resolved on the virtual cross-sections, granting a unique 3-D insight in tissue flooding and formation of cavities in ‘Braeburn’ tissue during the development of the disorder. Image analysis methods were applied to extract morphometric parameters such as porosity, anisotropy and connectivity to characterise microstructure. The discriminative power of these descriptors was proven by their ability to classify fruit tissue as healthy and disordered with a success rate of 97%. The observed distinct radial patterns of porosity, anisotropy and connectivity may help in explaining why ‘Braeburn’ is susceptible to BBD.status: publishe

Structural-mechanical analysis of cookies produced by conventional and 3D printing techniques

Little knowledge exists of the relationship between mechanical properties and microstructure of cookies. A cookie can be described as a solid matrix in which gas spaces of different sizes and shapes are embedded. Additive manufacturing or 3D printing has emerged as a novel method to produce cookies. The process of 3D printing is, however, significantly different from a conventional baking process. In order to assess the texture of 3D printed cookies relative to that of traditional cookies, in this study the mechanical and structural properties of cookies of different compositions and production methods were measured and analysed. Three-point bending tests were performed to determine Young’s modulus, failure stress and strain. X-ray micro-CT imaging at 5 µm pixel size was applied to characterise the 3D microstructure of the cookie samples used in mechanical testing. Of the microstructure properties, structure thickness distribution appeared to change Young’s modulus of cookies; which could be affected by the sugar and fat composition in traditional cookies. The structure of printed cookies strongly depended on both the printing method and the composition. Both particle size of the flour and the binder composition were significant. The structure: binder ratio was less effective to change structure. The final aims of this study are to combine knowledge to understand structure-property relationships of cookies incorporating observed structural properties and to construct a model capable of computing mechanical properties of foods from the microstructure and composition.status: publishe

Structure design of 3D printed cookies in relation to texture

In order to develop a model that allows for a better understanding of the interaction between the properties of the solid matrix, the structure and the mechanical behaviour of the cookie, both mechanical and structural properties need to be taken into account. To this end, a finite element model (FEM) was developed that predicts the mechanical properties of the structured product based on the material properties of the solid material used. The solid material mechanical properties were measured using compression tests with a universal testing machine. A larger variation of structures was analysed by means of FEM simulations, varying the size and shape of the air spaces and wall thickness of the structure. Structural parameters such as porosity, pore size and wall thickness were correlated to the mechanical properties such as Young’s modulus. In a next step these structures validated by means of mechanical compression tests on actual printed structures (by means of fused deposition modelling) with different air space distributions based on the 3D FE design files. The structure of the printed cookies will also be verified by means of 3D micro-CT imaging. Using this final correlation model, microstructure of the products can be engineered to achieve desirable texture properties in silico and create dedicated print files for additive manufacturing of cookies.status: publishe

Acoustic, mechanical and microstructural properties of extruded crisp bread

The aim of this work was to describe the texture and structure of crisp bread obtained with different extrusion parameters. The texture of different crisp bread samples was evaluated using a combination of acoustic and mechanical tests. The advantage of this measurement setup is the feasibility of simultaneous registering of the forceedeformation characteristics, sounds (using an acoustic envelope detector coupled to the texture analyser with a microphone) as well as mechanical vibrations (registered using a piezoelectric sensor) generated during a penetration test. All analysed samples of bread were products with a crisp texture that emitted audible sounds with a significant intensity that could be registered with a microphone as well as with a contact method. Micro-CT cross-section images showed the highly porous structure of the crisp breads but variant 3 appeared to have thicker walls and larger cells than the other breads.publisher: Elsevier articletitle: Acoustic, mechanical and microstructural properties of extruded crisp bread journaltitle: Journal of Cereal Science articlelink: http://dx.doi.org/10.1016/j.jcs.2013.03.010 content_type: article copyright: Copyright © 2013 Elsevier Ltd. All rights reserved.status: publishe

X-ray CT for quantitative food microstructure engineering: The apple case

Apple fruit is a major crop that can be supplied year-round due to low temperature storage in a controlled atmosphere with a reduced oxygen concentration and an increased carbon dioxide concentration. The low temperature and dedicated gas concentration levels are designed to provide optimal conditions that prevent ripening while maintaining the fundamental respiratory metabolism necessary for energy supply in the cells that ensures cell and tissue integrity during storage of the fruit. If the concentration of oxygen is too low or that of carbon dioxide too high, a fermentation metabolism is induced that causes the production of off-flavours, results in insufficient energy supply, leading to cell collapse and consequent tissue browning and cavity formation. The microstructural arrangement of cells and intercellular spaces in the apple create specific pathways for transport of the respiratory gasses oxygen and carbon dioxide. We used X-ray CT to characterise the changes in the microstructure of ‘Braeburn’ apple during the development of internal storage disorders. Multiscale modeling was applied to understand the changes in oxygen and carbon dioxide concentrations and respiration and fermentation rates in the apple during the disorder development in controlled atmosphere storage of ‘Braeburn’ apple fruit. The 3D microstructure geometries of healthy, brown tissue and tissue with cavities were created to solve the micro-scale gas exchange model for O2 and CO2 using the finite volume method. The apparent gas diffusivities of the tissue were calculated and implemented in the macroscale geometry of healthy and disordered apples to study in detail the changes in the respiratory metabolism of the fruit.publisher: Elsevier articletitle: X-ray CT for quantitative food microstructure engineering: The apple case journaltitle: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms articlelink: http://dx.doi.org/10.1016/j.nimb.2013.07.035 content_type: article copyright: Copyright © 2013 Elsevier B.V. All rights reserved.status: publishe

Designing Mechanical Properties of 3D Printed Cookies through Computer Aided Engineering.

Additive manufacturing or 3D printing can be applied in the food sector to create food products with personalized properties such as shape, texture, and composition. In this article, we introduce a computer aided engineering (CAE) methodology to design 3D printed food products with tunable mechanical properties. The focus was on the Young modulus as a proxy of texture. Finite element modelling was used to establish the relationship between the Young modulus of 3D printed cookies with a honeycomb structure and their structure parameters. Wall thickness, cell size, and overall porosity were found to influence the Young modulus of the cookies and were, therefore, identified as tunable design parameters. Next, in experimental tests, it was observed that geometry deformations arose during and after 3D printing, affecting cookie structure and texture. The 3D printed cookie porosity was found to be lower than the designed one, strongly influencing the Young modulus. After identifying the changes in porosity through X-ray micro-computed tomography, a good match was observed between computational and experimental Young's modulus values. These results showed that changes in the geometry have to be quantified and considered to obtain a reliable prediction of the Young modulus of the 3D printed cookies.status: Published onlin

Designing Mechanical Properties of 3D Printed Cookies through Computer Aided Engineering

Additive manufacturing or 3D printing can be applied in the food sector to create food products with personalized properties such as shape, texture, and composition. In this article, we introduce a computer aided engineering (CAE) methodology to design 3D printed food products with tunable mechanical properties. The focus was on the Young modulus as a proxy of texture. Finite element modelling was used to establish the relationship between the Young modulus of 3D printed cookies with a honeycomb structure and their structure parameters. Wall thickness, cell size, and overall porosity were found to influence the Young modulus of the cookies and were, therefore, identified as tunable design parameters. Next, in experimental tests, it was observed that geometry deformations arose during and after 3D printing, affecting cookie structure and texture. The 3D printed cookie porosity was found to be lower than the designed one, strongly influencing the Young modulus. After identifying the changes in porosity through X-ray micro-computed tomography, a good match was observed between computational and experimental Young’s modulus values. These results showed that changes in the geometry have to be quantified and considered to obtain a reliable prediction of the Young modulus of the 3D printed cookies

Characterization and model-based design validation of 3D printed cookies

Additive manufacturing is revolutionizing processing in many applications including 3D food printing. A Fused Deposition Modelling printing method was developed to produce cookies. In order to design food of particular texture, a fine element model was established to predict the mechanical properties of structured products. Cookie structures were engineered to achieve desirable texture properties in silico and dedicated print files were created for 3D printing. In order to validate the model, the properties of the printed cookies were measured and analysed. Compression tests were performed to determine Young’s modulus. X-ray micro-CT imaging was applied to characterize the 3D microstructure of the printed cookies samples. Micro-CT imaging provided a better understanding about the effects of the 3D printing process on cookie structure. Finally, a better fit of the prediction model was obtained by adjusting the model geometry to the scanned printed structure, which indicates the importance of structure integrity for mechanical properties of printed cookies.status: publishe