Laminates compression tests

Mechanical Property Testing. Mechanical tests were performed on both unirradiated and irradiated materials at -157°C, 24°C, and 121°C. Specimens were kept dry prior to testing in an environmental chamber mounted in a tensile testing machine. Tensile test specimens of [0]4, [10]4, [45]4, and [90]4 laminates were cut from 4-ply composite panels. All specimens were straight-sided coupons. For tension and shear tests the length/width aspect ratio was 8. For the compression tests the aspect ratio was 0.25 and the unsupported length was 0.64 cm. The [0]4 laminates were used to measure the ultimate tension and compression strength, Xit the axial... 

In general, other properties of the acetylated laminates showed, improved properties over control laminates. For example, acetylated laminates in compression tests parallel to grain showed a 3% increase in stress at proportional limit, 8% increase in ultimate strength, 6% decrease in MOE, and 21% increase in deformation at failure as compared to controls. In compression tests perpendicular to the grain, acetylated laminates showed a 30% increase in stress at proportional limit, 47% increase in ultimate strength, 21% increase in MOE, and 10% increase in deformation at failure as compared to controls. 

Brief mention may be made here of a compression test that measures the cohesion between layers of laminated tube as given in BS 2782. Method. 346A. This is covered more fully in Chapter 18. 

Compression testing is particularly difficult for PMCs due to the occurrence of macro- and microbuckling modes. The rectangular prism specimen in ISO 604 is not suitable for laminated composites, as these will split vertically between the laminate layers when loaded axially in the plane of the laminations. Variations on these designs arc suitable for compression, and tensile testing, in the through-thickness direction (i.e.. direction 3 in Fig. 1),... 

Most composites are available as relatively thin laminated sheets, so that tensile type specimens 2 mm to 4 mm thick arc not suitable for compression tests, as they fail by Euler column buckling. Three approaches have been used to avoid specimen buckling ... 

Rhead AT, Butier R, Baker N. Analysis and compression testing of laminates optimised for damage tolerance. Appl Compos Mater 2011 18(1) 85—100. 

The fracture toughness of the laminate material can be measured by a number of methods, some of which are shown in Fig. 4.32. The results will vary with different layup orientations. Other methods may be similar to the test specimens shown in ASTM-E-399 and may involve impact. Presently, the most widely accepted technique for evaluating the fracture toughness of a laminate or structure is a compression test after impact. Compression is a valid indicator without matrix support, the fibers will buckle, while the fibers do not need as much matrix support for tensile loading. 

Mechanical Properties. The performance of various polyester resin compositions can be distinguished by comparing the mechanical properties of thin castings (3 mm) of the neat resin defined in ASTM testing procedures (15). This technique is used widely to characterize subtle changes in flexural, tensile, and compressive properties that are generally overshadowed in highly filled or reinforced laminates. 

The laminate compressive hoop strength/stiflness of a filament-wound vessel can be evaluated using the externally pressurized ring test method [44] or the standardized ASTM D2586 test method. In the ASTM D2586 test method a filament-wound FRP cylinder is tested under hydrostatic pressure to simulate the loading conditions of a pressure vessel under an external pressure load. The main drawback of this test method is the influence of the end constraints on the test results. 

There are also ASTM methods for gasket material8 and laminated composite gasket materials9 which uses the expansion of a calibrated steel bolt to measure the force. The test is restricted to 22hrs compression, usually at 100°C. 

The metallic layers were examined either by conventional or cross-section TEM in a Jeol 200 Cx microscope. For the cross section preparation a sandwich of two laminates is made, glued face to face with an epoxy, cut in small pieces, mechanically polished, and then ion milled to a final TEM observation thickness. The plane section TEM sample are prepared by dissolving the PET in trifluoroacetic acid for 5 to 10 mn. The area observed, on plane section TEM, for the grain size calculation is close to 0.2 urn. For the adhesion measurements, test pieces consist of aluminum support (1 mm thick) double sided tape (Permacel P-94) PET (12pm) / evaporated aluminum/ ethylene acrylic acid (EAA) copolymer film. These laminates are prepared for the peel test by compression under 1.3 105 N.m2 at 120°C for 10 seconds. The peel test is performed by peeling the EAA copolymer sheet from the laminate in an INSTRON tensile tester at 180° peel angle and 5 cm min peel rate. 

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