# Nonlinear Dynamics of Vibro-Impacting Indenter
## 2 Experimental Setup  
This section describes, in detail, the main features of an experimental rig, which had previously been designed and manufactured. This includes its geometrical arrangements, dimensions and instrumentation, which facilitate data acquisition. The experimental rig had been designed to induce vibro-impact loading through an indenter on either metal or sandstone samples. This is made possible by means of a pneumatic actuator, as well as an electrodynamic shaker, so as to effect a static compressive force and sinusoidal variation in electromagnetic force. Figure 1a shows the experimental rig of the present work. The experimental rig was built to function in a way similar to a previous apparatus [28], which was developed based on [25] but with improved features for studying the behaviour of the indenter during its interaction with impacted material. The experimental rig was designed, manufactured and calibrated at the Centre for Applied Dynamics Research of the University of Aberdeen. The experimental rig mainly consists of two parts, namely, a piston-shaker-indenter part, which generates oscillatory motions of the indenter, and a restraint part, which holds the impacted material. Both parts are secured on the top of a metal plate and are configured to be co-axial and horizontally levelled on the plate. The experimental rig is capable of supplying a controlled axial vibration on the indenter for a wide range of pre-defined static forces, and it is described below. In the piston-shaker-indenter part of the experimental rig, an LDS electrodynamic shaker (Model: V530) is used to actuate the indenter mounted at one end and to generate the vibratory motions of the indenter for experiments. The electrodynamic shaker is attached to a rigid external frame, which is in turn mounted on the metal plate by means of four carriages and two linear guides. This arrangement constrains the electrodynamic shaker to move in one direction, as the shaker-frame assembly is actuated by a rod connected to a piston at the other end. The piston is a part of the pneumatic cylinder, and it provides the required static force to push and pull the electrodynamic shaker towards and from the restraint part of the experimental rig, respectively, in the horizontal direction. A control valve is used to control the flow and pressure of compressed air entering the pneumatic  
Figure 1: (**a**) Top view of the CADR experimental apparatus used for the present work. (**b**) Schematic of (**a**). (**c**) Geometry of the indenter. cylinder through the air hoses, and this permits the control of the actuation direction and the forcing magnitude of the piston, respectively. To ensure linear and smooth movements of the electrodynamic shaker, the pneumatic cylinder is used with a pressure regulator and bleeding valves. A load cell is attached between the back of the indenter and the shaker armature. An accelerometer, which is not shown in the figure, is mounted to the armature assembly during experiments. A linear variable differential transformer (LVDT), which is also not shown in Figure 1a, is mounted on the rigid frame of the electrodynamic shaker, and its core is attached to the restraint part of the experimental rig during experiments. The restraint part is mainly a fixture that firmly holds the metal or sandstone samples in place for experiments, and the restraint part is mounted on the same platform as the piston-shaker-indenter part. A schematic of the experimental rig is illustrated in Figure 1b. The axial vibration of the indenter is measured using a KISTLER accelerometer. The impact forces are measured using a KISTLER dynamic-type strain gauge load cell (Model: 4576A5). The load cell is able to measure dynamical forces of up to 5 kN. As for the measurement of the displacement of the indentation, the LVDT is used. The LVDT provides an output voltage signal ranging between 0 and 10 V, which corresponds to a displacement variation of between 0 and 50 mm.