MATERIAL MECHANICAL BEHAVIOUR ANALYSIS OF SPRUCE AND TEAK WOOD DUE TO PRESSURE LOADS AT HIGH STRAIN RATE WITH FINITE ELEMENT METHOD

• Main Author: Adityo Teguh Prabowo, Fx
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/37052
• Institution: Institut Teknologi Bandung

The strain rate is the rate of deformation caused by the forces acting on a material. Strain rate affects the strength of the material. In this case, the higher strain rate the higher material strength will be. Wood material as an anisotropic material has complex behavior. In the existing literatures, wood mechanical data is only available under static loading conditions, material data for dynamic and impulsive loading conditions are still rarely found. One tool that can be used to determine the mechanical behavior of material under dynamic and impulsive conditions is Split Hopkinson Pressure Bar (SHPB) test. SHPB is able to measure the behaviour of material at a high strain rate between 1000 - 10000/s. Tests were carried out on spruce (picea abies) and teak (tectona grandis) specimens directed parallel direction of fiber (longitudinal) and in the perpendicular direction of fiber (transversal). Spruce and teak woods were chosen as spruce wood represents softwood and teak wood represents hardwood, respectively. The speciments tested are of cylindrical form with 20 mm diameter and either 20 mm or 24 mm height. There are two types of SHPB bar, steel and acrylic/PMMA. Steel bar is used to test the longitudinal direction of spruce wood and teak wood and for the transversal direction of teak wood. Acrylic material / PMMA (polymethyl methacrylate) bar is used to test the tangential and radial directions of spruce wood. The dimensions of the bars is 25 mm diameter and 1250 mm length for incident and transmission bars and 375 mm for striker bars length. Tests are carried out at strain rates between 1800/s to 2900/s. The numerical analysis is carried out using finite element software to simulate wood material under high strain rates conditions. The simulation of SHPB bars material uses a type of elastic modeling and the simulation of wood material uses honeycomb material type. The "automatic surface to surface" contact type is to simulate when there is a collision between two surfaces and "constraint nodes to surface" contact type is to avoid the contact surface one penetrates the other contact surface. Numerical simulation results are validated with experimental results. In the numerical simulations, firing speed is increased to obtain the strain rate that is similar to that of the experiment. By magnifying the firing speed in numerical simulations, the yield stress obtained from the numerical simulations is similar to that of the experimental analysis with less than 10% differences.