36.2 Experimental The HPHT in-situ strain measurements were conducted in the in-house developed HPHT in-situ thermomechanical testing and analysis system, as illustrated in Fig. 36.1. The HPHT in-situ thermomechanical testing and analysis system consists of an HPHT autoclave, a controlled cell oven, a hydraulic driving system, a mechanical test load frame, a high-pressure gas source and a nitrogen pressure control system. The autoclave can accommodate the in-situ tensile load frame and the environmental medium under high temperature and high pressure. The system can accommodate standard tensile tests per ASTM D638. All components exposed to the test environment are made of high-strength, corrosion-resistant alloys. The hydraulic driving system includes an actuator, a servo valve, a service manifold and a hydraulic power unit. The load frame connects the hydraulic actuator and the loading train that includes a load cell and a loading rod that passes through a hightemperature, low-friction reciprocating seal in the top plug of the autoclave. The hydraulic driving system and the mechanical test frame are controlled by a full-functional MTS controller for operation and data acquisition. The nitrogen pressure control system can control the autoclave pressure accurately to within 34 KPa (5 psi). The in-situ test system is rated to a 50 KN (11.2 kip) loading capacity in fluid and gas environment up to 260 C (500 F) and 69 MPa (10,000 psi). Figure 36.2 shows a photograph of the entire in-situ test rig with its controller and hydraulic pump, and more detailed information on the HPHT in-situ thermomechanical testing and analysis system can be found in author’s earlier publications [8, 9]. The in-situ test system was used in combination with the HPHT in-situ extensometer, as illustrated in Fig. 36.3, purchased from Psylotech, Inc. with certain improvements and modifications for the HPHT in-situ strain measurement application. The HPHT in-situ extensometer is an AC excited Wheatstone bridge with inductors replacing traditional resistive strain gages constructed with high-strength, corrosion-resistant alloys to withstand the corrosive hot-wet testing conditions. In this design configuration, as long as the resin sealed inductors can withstand the hot-wet environment, the sensor can operate. The HPHT in-situ extensometer consists of two sets of self-gripping pairs, one pair for measuring transverse strain (top on Fig. 36.3a, b), and another pair for measuring axial strain (bottom on Fig. 36.3a, b). Each pair of grips has 30 knife edges and loading springs for efficient gripping onto the test specimens. Material tested in this study is an E-glass fabric reinforced epoxy composite laminate, commonly used in oilfield applications. The test specimens were cut from the laminate panel in principal fiber direction to 178 mm (7 in.) long, 19.1 mm (0.75 in.) wide and 3.2 mm (0.125 in.) thick as straight-side tensile specimens per ASTM D3039. Figure 36.3c shows a test specimen mounted in the in-situ tensile grips and load frame with the in-situ extensometer installed, ready to be submerged into the high-pressure autoclave for the in-situ testing. Fig. 36.2 Overall view of a HPHT in-situ test rig with the control system and hydraulic power unit 36 HPHT In-Situ Strain Measurement of Polymer Composites for Oilfield Applications 297
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