Failure and Damage in Cellular Materials
This chapter presents the main aspects on failure and damage of cellular materials. Tensile, compression and fracture mechanics properties of plastic foams are presented and the main influence factors are investigated: density, temperature, loading speed
- PDF / 3,551,096 Bytes
- 72 Pages / 439.37 x 666.142 pts Page_size
- 15 Downloads / 269 Views
*
and Dan M. Constantinescu
†
Universitatea Politehnica Timi¸soara, Timi¸soara, Romania Universitatea Politehnica Bucure¸sti, Bucure¸sti, Romania
Abstract This chapter presents the main aspects on failure and damage of cellular materials. Tensile, compression and fracture mechanics properties of plastic foams are presented and the main influence factors are investigated: density, temperature, loading speed and loading direction. Particularly for fracture toughness the mixed mode loading and size effects are discussed. The potential of digital image correlation as a tool to observe the damage of polyurethane foams is also highlighted.
1
Introduction
Foam materials have a cellular structure and hence behave in a complex manner, especially under conditions of progressive crush. This crush behavior is dependent on the geometry of the microstructure and on the characteristics of the parent material. Foam materials are often used as cores in sandwich construction, and in this application the material can be subjected to multi-axial stresses prior to and during crush. Well-known advantages of cellular materials are their excellent ability for energy adsorption, good damping behavior, sound absorption, excellent heat insulation and a high specific stiffness combined with a low weight. The combination of these properties opens a wide field of potential applications, i.e. as core materials in sandwich panels. A good knowledge of the behavior of different grades of foams is important for being able to design high performance sandwich composites adapted to the special needs of a particular application (Gibson and Ashby, 1997; Mills, 2007). The properties of cellular materials are influenced by the properties of solid material (polymers, metals, ceramics), by the cellular structure topology (open or closed cells) and relative density ρ/ρs , with ρ density of cellular material and ρs the density of the solid material (Ashby, 2005). Polyurethane (PU) foam is an engineering material for energy absorption and has been widely used in many applications such as packaging and cushioning. The mechanical testing of rigid PU foams under compression H. Altenbach, T. Sadowski (Eds.), Failure and Damage Analysis of Advanced Materials, CISM International Centre for Mechanical Sciences DOI 10.1007/978-3-7091-1835-1_3 © CISM Udine 2015
120
L. Marsavina and Dan M. Constantinescu
in the rise and transverse direction gives different deformation responses in each direction which are attributed to the anisotropy in the internal cellular structure. There are two approaches to the modeling of the constitutive behavior of foam materials. The first is continuum modeling. A number of theories have been presented, namely the critical state theory, which is used in standard finite element codes such as ABAQUS, and enhancements have been developed to take account of specific foam behavior (Warren and Kraynik, 1997; Akay and Hanna, 1990; Mines et al., 1994; Mines and Jones, 1995; Li and Mines, 2002). To calibrate such a numerical model based on material behavi
Data Loading...
