Recent investigations conducted by John Deere Des Moines Works (JDDMW) on the possible adverse effects of recent industry wide increases in tractor standby pressure and its effect on hydraulic hose life prompted a follow-up study at the John Deere Product Engineering Center (PEC). The JDDMW investigation extensively used the Hose Fatigue Life Program that is based on the cumulative damage theory of metals. Because no known research has been done regarding the conservativeness of this program, a series of tests concerning variables affecting the fatigue life of hydraulic hoses was initiated. The purpose of the study was to determine the degree of confidence in predicting the fatigue life of hydraulic hoses with known variable pressure histories. The study consisted of evaluating four variables which the program did not fully take into consideration. These variables were time at load, bend radius, pressure range, and pressure mean. Testing was conducted using a single manufacturers single wire 9.5 mm (3/8 in.) ID hydraulic hoses and all conclusions made in this report are exclusively for this manufacturer's hose.
Results from the study have shown the Hose Fatigue Life Program can be used to make accurate hose life predictions when the actual Pressure-Life curve of the hose in question is known and when the history of the hose is mostly zero-to-max pressure cycles.