Mechanical properties of cereal (starch-based) extrudates are perceived by the final consumer as criteria of quality. We investigate one of the important characteristics of extrudates, mechanical hardness, which is one of the main texture parameters. Texture quality has an influence on taste sensory evaluation, and thus on the acceptability of the product. Characteristics that have great influence on acceptability are crispness, elasticity, hardness and softness. These attributes are narrowly related to, and affected by, the process parameters. A 2-level-4-factor factorial experimental design was used to investigate the influence of temperature of expansion, screw speed, feed moisture content and feed rate, and their interactions, on the mechanical hardness of extrudates. Feed moisture content, screw speed and temperature are found to influence, while feed rate does not have significant effect on extrudate hardness. Mechanical properties of specimens were measured by means of compression testing, based on the concept of nominal stress, using a universal testing machine and special grips that were constructed for this purpose.

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Standard fracture toughness tests require standard specimens with the presumption that mechanical properties are uniform in the crack growth direction. Standards for crack tip opening displacement (CTOD) fracture tests prescribe remote crack mouth opening displacement, which can lead to inadequate results in the case of heterogeneous materials properties. This paper describes the application of an object grating method (OGM) on the fracture behaviour of a heterogeneous specimen. Fracture behaviour is described by measuring deformation on the surface of a specimen, in terms of CTOD and, consequently, by strain determination. An OGM is advantageously used when measuring modified CTOD tests on two specimens with an initial crack in a macroscopic heterogeneous welded joint. Results significantly show that fracture behaviour depends on the material in the vicinity of the crack tip concerning the direction of crack propagation.

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The rapid development of a variety of Additive Manufacturing (AM) techniques is witnessed by the large interest of the scientific community. Among the numerous new features offered by these techniques, very lately the possibility of including cracks of any shape, direction, and position inside AM samples to validate FEM models was explored. Therefore, the necessity arose of full-field measurement techniques that would allow the evaluation of the fracture mechanics parameters in the cases of both linear elastic and partially plastic materials, as a function of the fracture modes. Invented in the ’80 of the XX century, the Digital Image Correlation (DIC) in recent years has taken place in nearly every laboratory. It is used to measure displacements, and by numerical differentiation or coupling with Finite Element Method, to calculate strains at different spatial scales. In particular, two procedures that were successfully employed on a specific kind of specimens, based on DIC at a small scale near the crack-tip, in this paper are shown in detail.