A numerical and experimental investigation into size effects within loaded additively manufactured cellular solids

  • Martin Dunn

Student thesis: Doctoral Thesis

Abstract

The behaviour of heterogeneous materials when loaded cannot be adequately described by classical elasticity as it doesn’t account for the presence of internal length-scales. Higher order theories such as micropolar elasticity may be more appropriate, though the additional elastic constants required to fully describe such materials are hard to identify experimentally. In micropolar theory a size effect is predicted in bending and torsion which is revealed as an increase in relative stiffness with decreasing size at scales approaching the cellular microstructure. Thus, at the microstructural level, size and scale becomes an important consideration. Hence, materials which appear homogeneous at a large scale may be heterogeneous at smaller scales when overall size approaches that of the cellular structure. Addressing this issue requires aclear understanding of how scale influences the material’s mechanical properties. Here, the mechanical response of periodic, cellular lattices has been explored within the context of micropolar theory by conducting discrete numerical simulations and experimental tests. It will be shown that the size effects displayed in bending and torsion are strongly dependent on the cellular volume fraction and sample section second moment of area associated with the distribution of the matrix material within the cells comprising the section. Crucially however, these effects may be masked by surface texture and localised loading conditions. Despite the inherent difficulties associated with experimental testing, the size effects which are predicted by micropolar theory are identified experimentally in an additively manufactured cellular material.The observed size effects showed reasonable agreement to numerical simulations performed in ANSYS. Demonstrating that the behaviour of structured cellular materials with deterministic properties, fabricated by additive manufacturing, can be described by more generalised deformation theories is important as it enables the design and development of new and novel materials to be explored and exploited in lightweight structural applications.
Date of Award1 Apr 2017
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorMarcus Wheel (Supervisor) & Philip Riches (Supervisor)

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