# Design and Experimental Analyses of Hybrid Piston Rods Used in Hydraulic Cylinders under Axial Load
## 1 Introduction  
In recent years, the weight of construction and heavy industrial machinery is considered a problem, as it contributes to higher fuel consumption and thus more emissions and environmental damage. Various methods are being considered to reduce weight. There is a continuous and progressive process of weight reduction in structural components. This weight reduction in structural components not only reduces fuel consumption but also increases the performance of the machine due to reduction in inertial forces. The objective of this study is to replace conventional steel hydraulic cylinder rods with cylinder rods made of a combination of steel and CFRP to reduce the weight of the piston rod without compromising its structural strength. This lightweight piston rod is to be used in a hydraulic cylinder, which in turn reduces the weight of the hydraulic cylinder. If the weight of the hydraulic cylinder is reduced by 1 kg, the weight of the construction machine can be reduced by up to 6 kg, that is, we can reduce the weight of the construction machine up to six times by reducing the weight of a single cylinder. This is because a single machine uses more than 6 to 8 hydraulic cylinders which vary in size and function [1]. In a hydraulic cylinder, the piston rod (as shown in Figure 1) is the heaviest component and accounts for about 40% of the total weight of the cylinder. The piston rod is usuallymade of solid steel which is capable of withstanding the buckling load. Buckling is a sudden, large and unstable deflection in the lateral direction that occurs at a critical value when the compressive load increases slightly. This buckling in the piston rod of a hydraulic cylinder is caused by the combination of hydrostatic pressure and external forces that reduce the load carrying capacity of the piston rod. When the piston rod buckles, it collapses and can be bent (see Figure 2), causing serious accidents and malfunctions. Therefore, buckling resistance is a major hazard for the piston rod, which must be protected against such failures, and designers must take precautions against such failures in the design and development of hydraulic cylinders [2,3]. Our plan is to either replace the piston rod with another material or minimize the use of steel in piston rods without compromising their load carrying capacity, i.e., their buckling strength. In recent years, almost all heavy industries have realized the importance of weight reduction and started looking for lightweight materials. Most industries started switching from steel to other high-grade metals like titanium, magnesium, etc., which are highly resistant to corrosion from acid attacks and external environmental conditions. They also have lower density than steel but are much more expensive than steel. Figure 3 below shows how the cost varies with the weight of the materials [4]. With the introduction of polymers in the mid-1960s, most industries turned their attention to these materials for their purposes. This is due to the fact that polymers are very  
Figure 1: Hydraulic cylinder. Figure 3: Cylinder design: weight vs. price [5]. Figure 2: Buckling failure pattern. strong yet lightweight material. It is two times stiffer and five times stronger than steel and significantly lighter than steel. These combined properties make it an ideal manufacturing material that is preferred by engineers and designers in manufacturing. These polymers are naturally anisotropic, which means their strength and properties are directional, making them even more superior as they can carry the load in their stronger direction. Their properties are mainly influenced by the choice of fibers used, the orientation of the fibers, type of resin and the curing conditions. Depending on the application, different techniques are used to produce them, namely, hand lay-up, resin transfer molding, infusion, putlursion, filament winding, autoclave, etc.