Design and Experimental Analyses of Hybrid Piston Rods Used in Hydraulic Cylinders under Axial Load

Abstract

Composite hydraulic cylinders are used to reduce the weight of construction equipment such as aerial work platforms or excavators. The weight is compensated by manufacturing hydraulic cylinders from Carbon Fiber Reinsforced Plastic (CFRP), but this is expensive. Therefore, this study investigated a hybrid hydraulic cylinder, which is a combination of CFRP and steel, considering both performance and cost. The conventional hydraulic cylinder rods are made of steel, which can prevent failure due to buckling under push load (Push) or failure under alternating push-pull load (Push-Pull) or pull only. In this paper, we discuss how the failure threshold for these two mechanisms can be increased by making the piston rod from a hybrid material. In order to develop this lightweight hybrid piston rod for hydraulic cylinders that meets the buckling strength requirements of the original steel rod, CFRP is used as a substitute, which has significant buckling strength against compressive loading and, most importantly, is lighter than steel. The substitution is done either by replacing steel completely with CFRP or by reducing the volume of steel and sheathing it with CFRP. Numerical and experimental studies are carried out to understand the strength and behavior of piston rods when they are replaced by different combinations of composite materials for the given load. For this study, two different piston rod designs with various design parameters were considered, and their respective behavior under loading was discussed. The effect of compressive loads on CFRP wrapped steel parts and buckling strength as a function of fiber orientation, stacking angle and number of CFRP layers was investigated using experiments. The study demonstrated the usefulness of steel-CFRP composites to reduce weight and their influence on buckling load in hydraulic cylinders.