The Anisotropy Effect of Closed-Cell Polyisocyanurate (PIR) Rigid Foam under Quasi-Static Compression Loads (original) (raw)
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This paper presents the effect of loading speed, material orientation and density on the properties of cellular materials, such as rigid polyurethane foams, subjected to compressive load. These parameters have a very important role because in many applications, foams are used as packing materials or dampers which require high energy impact absorption. The experimental tests were carried out on specimens in the form of cubes. The specimens were subjected to uniaxial compression with loading speed of 2 mm/min, except samples for determining the effect of loading speed where 1, 5, 10 and 20 mm/min loading speeds were used. One of the most significant effects of mechanical properties in compression of polyurethane foams is the density, but also the loading speed and material orientation influences the characteristics in compression.
Mechanical Characterization of Rigid PUR Foams Used for Wind Turbine Blades Construction
Cellular solids are made up of an interconnected network of solid struts or plates which form the edges and faces of cells. Cellular materials are widely used in engineering applications because they have certain properties that cannot be elicited from many homogeneous solids. Besides many other applications, polymeric cellular materials are used in the construction of wind turbine blade parts or entire sections. This research studies blade – section as a core (foam) inserted between the upper and lower surfaces (blade skin). For this purpose we will study the behaviour of PUR foam materials in various mechanical loading such as: compression tests (static and dynamic) and fracture toughness tests (static and dynamic) on notched specimens. We will study in detail the influence of density (in range of 40 – 200 kg/m3), influence of loading rate (from 1.67.10-4 m/s – static tests to 6 m/s – impact tests), influence of forming plane (in plane and out of plane loading direction), influence of temperature (from 20°C to 100°C) and size effect on the mechanical properties. Cellular materials have plastic plateau and densification in compression, while in tensile they are quasi – brittle. The most important mechanical properties which will be studied are Young’s modulus, yield stress, plateau stress, densification and fracture toughness. The experimental program was specifically designed according to the aim of the work. Also to the end of this paper is shown a microstructural analysis for both before (initial surface) and after (broken surface) compression and three – point bending tests. As a conclusion we can say that one of the most significant parameter on the mechanical properties for cellular materials is the density. Hence, the mechanical properties of foams can be controlled, making them attractive in structural application requiring particular strength or stiffness to weight ratios.