Experimental Investigation

Testing of the ROPS for the K275 bulldozer was performed at ½ scale at QUT’s testing laboratory。 In order to meet the performance criteria of the Australian Standard AS2294- 1997, a specialised testing frame which could deliver loads in the lateral, vertical and longitudinal directions of the ROPS was designed, fabricated and assembled at the QUT structures laboratory。 The testing frame was fabricated primarily from hot rolled structural steel sections that were securely mounted to the strong testing floor of the laboratory。 The general arrangement of the testing frame setup, showing the position of the major structural members is shown in Figure 2。 The testing frame was arranged in a manner that enabled

static loads to be applied to the ROPS in the direction of its lateral, vertical and longitudinal axes。 On the strong floor horizontal gridlines, as shown in the Figure, were assigned to assist with the erection of the testing frame。 A series of two-dimensional frames each consisting of two columns and two tying beams were arranged along the grid lines 1, 3 and 4。 The frames were then linked together by means of a longitudinal beam that was supported by the uppermost tying beam of each frame。 Two additional horizontal members linking grids 1 and 3 were also provided in the frame assemblage。 The first beam which was positioned along grid B acted as a jacking beam to enable delivery of the lateral load to the ROPS。 The second beam which was positioned along grid D was designed to restrain the column supporting the ROPS from twisting during the lateral loading sequence。 Diagonal bracing members were also positioned predominantly at loading or reaction zones in the frame in order to minimize the displacement of the loading frame during jacking and to assist with transfer of reaction forces into the strong floor。

The half scale K275 ROPS model was rigidly mounted to the specially fabricated loading frame that could safely apply the required lateral, vertical and longitudinal loads, as shown in Figure 3。 Full penetration butt welds were used between the base of the ROPS and the stiff lower crosshead to simulate full base fixity and to replicate the fixity condition of the in- service ROPS/chassis assembly of the K275 bulldozer。 The ROPS was subjected to the loading and energy requirements of AS2294-1997 which involved the consecutive loading and unloading of the ROPS along its lateral, vertical and longitudinal axes。 The formulae for calculating the lateral, vertical and longitudinal loads and the required lateral deflection according to AS2294。2-1997 are given in column 2 of Table 2 in which M is the mass in kg, (and appropriate scaling factors have been inserted for the ½ scale ROPS model)。 The load and energy magnitudes for this particular ROPS model are given in column 3 of Table 2。

Instrumentation and measurement parameters

Strain and deflection measurements were recorded for each loading sequence by using a 120 channel VXI data acquisition system。 Four strain rosettes were attached to the top and  base of each post of the ROPS and strain recordings were taken at consistent intervals during the lateral loading stage only。 Deflection of the ROPS during each loading stage was measured using LVDT’s that were positioned in the direction of the applied load。 Each LVDT was securely mounted to an independent steel frame which enabled true deflection readings to be taken that were free of any loading frame movement。 Figure 4 shows (through views from two opposite directions) the positions of the strain rosettes and the LVDTs throughout the ROPS。 Rosettes A and C were positioned at the top of the right and left posts, while rosettes D and B were positioned at the base of the right and left posts respectively。 Loads were generated for each loading stage using hydraulic rams that were powered by an electric pump。 Each ram was calibrated prior to testing using the Tinius Olsen universal testing machine。 From the calibration process, suitable load-voltage coefficients were obtained which were included in the data acquisition software。 These coefficients were used  to convert the recorded pressure reading from the hydraulic rams into suitable force measurements。