A polyethylene (PE) liner is the basic element in high-pressure type 4 composite vessels designed for hydrogen or compressed natural gas (CNG) storage systems. Liner defects may result in the elimination of the whole vessel from use, which is very expensive, both at the manufacturing and exploitation stage. The goal is, therefore, the development of efficient non-destructive testing (NDT) methods to test a liner immediately after its manufacturing, before applying a composite reinforcement. It should be noted that the current regulations, codes and standards (RC&S) do not specify liner testing methods after manufacturing. It was considered especially important to find a way of locating and assessing the size of air bubbles and inclusions, and the field of deformations in liner walls. It was also expected that these methods would be easily applicable to mass-produced liners. The paper proposes the use of three optical methods, namely, visual inspection, digital image correlation (DIC), and optical fiber sensing based on Bragg gratings (FBG). Deformation measurements are validated with finite element analysis (FEA). The tested object was a prototype of a hydrogen liner for high-pressure storage (700 bar). The mentioned optical methods were used to identify defects and measure deformations.
The paper presents the measurements and the analysis of deformations between lay-ers and the outside surface of a multilayer filament wound composite pipe. The pipe was made through the hoop wrap of roving stripes hence ring-shaped samples were prepared for test purposes. Carbon fibers and glass fibers were used for winding. In the course of their manufacturing, strain gauges and fiber optic sensors were placed be-tween the composite layers. Then, the strength tests were performed. The samples were subjected to the internal pressure of 30 MPa. During the tests peripheral defor-mations were measured on outside surfaces of individual layers of the structure.
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