# Design and Experimental Analyses of Hybrid Piston Rods Used in Hydraulic Cylinders under Axial Load
## 4 Summary and Conclusions  
This paper is concerned with the experimental investigation of the buckling strength of piston rods in hydraulic cylinders subjected to high compressive loads and made of steel and composite materials. First, a finite element analysis using ABAQUS/standard (LANCZOS method) was performed to determine the bending stress induced by the buckling load in a steel rod with different diameters. Experimental analysis was carried out on hybrid bars with different volume of CFRP and steel at constant length. The following was found:  
1. The buckling load is significantly affected by the percentage of CFRP volume in the hybrid bar, regardless of whether it is a solid or hollow bar. The higher the CFRP volume, the better the buckling load carrying capacity of the hybrid rods.
2. The influence of the number of laminate layers on the buckling load depends largely on the angle and orientation of the laminates. They show better strength when the number of laminates is between 30 and 50.
3. For axial load, 0\({}^{\circ}\) laminate layers bear the largest load compared to other laminate layers, so their number should be larger compared to other laminate layers. However, their volume should not exceed 50% of the total laminate layers. If their volume is more than 50%, the load carrying capacity of the hybrid bar will decrease. The best range is between 25% and 35% for higher buckling loads.
4. The buckling load carrying capacity of the hybrid rod increases as the volume of the 45\({}^{\circ}\) laminate increases, and a range of 10% to 20% is recommended for best results. This range could be due to the fact that 45\({}^{\circ}\) laminate layers resist the bending induced by 0\({}^{\circ}\) laminate layers during axial loading, which further increases the buckling load capacity of the hybrid rod.
5. The influence of 90\({}^{\circ}\) laminate plies on the buckling load capacity of the hybrid rod is much smaller and almost negligible.  
It can be assumed that the buckling load carrying capacity of the hybrid bar is significantly affected by the change of CFRP volume fraction, number of laminate plies, fiber angle and fiber orientation.  
Figure 18: Change in buckling load as a function of percentage of 90\({}^{\circ}\) laminate in CFRP.  
This paper reports the main results of an investigation on the design and experimental testing of hybrid piston rods for hydraulic cylinders under axial load using steel and CFRP. The main research results aim to design and fabricate a lightweight hybrid rod that can withstand the maximum buckling load. Preliminary comparative analysis has been carried out for both solid and hollow steel rod with different volume of CFRP material. The steel composite piston rod used in hydraulic cylinders shows a weight reduction of up to 76% compared to a piston rod made of traditional mild steel. Research is therefore still ongoing, both in terms of structural and technological issues and of a comparative economic evaluation of the various solutions developed.  
Conceptualization, P.K.S.P.; methodology, P.K.S.P.; software, P.K.S.P.; validation, P.K.S.P. and S.-S.L.; formal analysis, P.K.S.P.; investigation, P.K.S.P.; resources, P.K.S.P. and S.-S.L.; data curation, P.K.S.P.; writing--original draft preparation, P.K.S.P.; writing--review and editing, P.K.S.P. and S.-S.L.; visualization, P.K.S.P.; supervision, S.-S.L.; project administration, P.K.S.P. All authors have read and agreed to the published version of the manuscript.  
No funding acquired for this Project.  
Not applicable.  
The authors declare no conflict of interest.