Constitutive modelling of skin ageing

The objective of this chapter is to review the main biomechanical and structural aspects associated with both intrinsic and extrinsic skin ageing, and to present potential research avenues to account for these effects in mathematical and computational models of the skin. This will be illustrated through recent work of the authors which provides a basis to those interested in developing mechanistic constitutive models capturing the mechanobiology of skin across the life course

High-dynamic compressive and tensile strength of specimens made of cementitious materials

The strength of specimens made of cementitious materials increases with increasing loading rate. Herein, themodel of Fischer et al. (CCR 58, 2014, 186–200) is revisited in the context of high-dynamic compression andextended to high-dynamic tension. The model is based on the assumptions (i) that cracking will start if the quasistaticmaterial strength is reached, and (ii) that the high-dynamic strength gain refers to the increase of the stressduring the failure process of the tested specimen. The model explains the behavior of cylindrical specimens madeof dry cement paste, mortar, and concrete, subjected to high-dynamic compression. It also elucidates the performanceof cylindrical specimens made of dry mortar and concrete, subjected to high-dynamic tension. It isconcluded that the high-dynamic strength gain is a structural effect and that structures will be damaged if thedynamic stress exceeds the quasi-static strength, no matter how fast the stress is increased and how short thestress pulse lasts.Austrian Science Fund (FWF

Early-Age Evolution of Strength, Stiffness, and Non-Aging Creep of Concretes: Experimental Characterization and Correlation Analysis

Six different concretes are characterized during material ages between 1 and 28 days. Standard tests regarding strength and stiffness are performed 1, 3, 7, 14, and 28 days after production. Innovative three-minute-long creep tests are repeated hourly during material ages between one and seven days. The results from the standard tests are used to assess and to improve formulas of the fib Model Code 2010: the correlation formula between the 28-day values of the strength and the stiffness, and the evolution formulas describing the early-age evolution of the strength and the stiffness during the first four weeks after production. The results from the innovative tests are used to develop a correlation formula between the 28-day values of Young’s modulus and the creep modulus, and an evolution formula describing the early-age evolution of the creep modulus during the first four weeks after production. Particularly, the analyzed CEM I concretes develop stiffness and strength significantly faster than described by the formulas of the Model Code. The creep modulus of the investigated concretes evolves significantly slower than their strength and stiffness. Thus, concrete loaded at early ages is surprisingly creep active, even if the material appears to be quite mature in terms of its strength and stiffness.Austrian Research Promotion Agency (FFG