Sandwich tensile test

Figure 2 Tensile adhesion test geometries (a) pi tensile test, ASTM D-897 (b) bar and rod tensile test, ASTM D-2094 (c) sandwich tensile test, ASTM D-257 (d) cross-lap tension test, ASTM D-1344.

Coating with Bulk Polybutadiene. E-glass fabric was embedded In Firestone s Diene 35 NFA using procedures very similar to those used to prepare peel test specimens. Rubber, which had been mill-mixed with 0.05% dlcumyl peroxide, was premolded between Mylar sheets to the desired thlckness(0.308, 0.151, or 0.100 cm) and size ( 30.5 X 18 cm) by molding for 1 hour at 60 C. and 40,000 lbs/5" ram. Fabric was cut so that the final size was at least one Inch smaller than the rubber sheets In all directions. A sandwich was made from the fabric and two premolded rubber sheets of the same thickness and about half the total thickness of the final sandwich. The sandwich was cured In a press for 2 hours at 150°C and 5000 lbs/5" ram. In the cured specimen the fabric was embedded In the center of the molded specimen (0.15 -0.40 In thick). Samples were Immensed In alkali before cutting to size for tensile tests. 

Apart from the short beam shear test, which measures the interlaminar shear properties, many different specimen geometry and loading configurations are available in the literature for the translaminar or in-plane strength measurements. These include the losipescu shear test, the 45°]5 tensile test, the [10°] off-axis tensile test, the rail-shear tests, the cross-beam sandwich test and the thin-walled tube torsion test. Since the state of shear stress in the test areas of the specimens is seldom pure or uniform in most of these techniques, the results obtained are likely to be inconsistent. In addition to the above shear tests, the transverse tension test is another simple popular method to assess the bond quality of bulk composites. Some of these methods are more widely used than others due to their simplicity in specimen preparation and data reduction methodology. 

A similar specimen design uses a sandwich construction with a dissimilar material bonded between the two cylindrical halves of the button specimen. This design is commonly used to measure the tensile strength of adhesives between dissimilar materials or if the adherend does not have the strength or characteristics to be machined into the shape of the button specimen. With some modifications in the dimensions, the button tensile test has also been adapted for testing adherence of honeycomb-cover sheets to the core (ASTM C 297). 

Fig. 16 Reactive sandwich moulding - image of fractured specimen afitea- tensile test, PTFE polyamide bulk material on the fracture surface of the polyamide material...

The measurement of compressive properties of plastics is covered by ISO 604 [44]. Unlike with the tensile test a single document is able to cover a wide range of materials, since test geometries and other conditions tend to be less variable between types of plastic than is the case for tensile testing. Nevertheless, there arc types of materials that the standard does not purport to cover, and these include textile reinforced plastics, cellular materials, and sandwich constructions involving cellular materials. 

ASTM D-1344 describes a cross-lap specimen of the type shown in Fig. 2d for determining tensile properties of adhesive bonds. Wood, glass, sandwich, and honeycomb materials have been tested as samples in this general configuration. Even under the best of circumstances, one would not anticipate the stress distribution in such a case to be very uniform. The exact stress distribution is highly dependent on the relative flexibilities of both the cross beams and the adhesive. Certainly, caution must be exercised when comparing tensile strength from this test with data obtained from other tensile tests. Probably for these reasons, this test is scheduled by ASTM for discontinuation. 

The tensile test gives mean values for the tensile moduli which are broadly in agreement with values predicted by theory. The values match very well especially for the laminate LI. For the sandwich construction SI and S2 a slight difference appears, perhaps because of their intrinsic structure. Theory therefore provides good estimates for tensile moduli. 

As for the tensile test, the flexural test results are in general agreement with the values predicted theoretically, except for S2 but the large difference here can be attributed essentially to its particular failure mode, which is induced by its geometry (i.e. thick upper skin and non-symmetric sandwich construction). 

Both the pi-tensile and bar and rod tensile tests can be modified to test materials which are not easily fabricated into adherends. These materials may be glasses, elastomers, or thin films. The test specimens are prepared by forming a sandwich of the particular material, for example, as shown in Figure 4. The main consideration in this test is that the adhesion between the adhesive and sample ends must be greater than that between the adhesive... 

As with tensile tests, it is sometimes necessary to test dissimilar materials in shear or materials which cannot be easily fabricated into adherends. For these cases, ASTM D3164-73 describes the testing of a lap shear sandwich joint. The test specimens consist of two metal adherends, typically 0.064 inch thick aluminum, the structural adhesive, and a 0.010-inch thin film of plastic. The sandwich joint is shown in Figure 8. 

Figure 33 Pure tensile test on honeycomb sandwich panel — clamps axis must be perfectly aligned in order to avoid any cleavage effect.

Sandwich flat tensile test (a) and sample after failure test (b)... 

The effect of silanes on the bond strength of two epoxide adhesives to glass is shown in Table 13. The test mode was that of Sandwich Butt Tensile in which a glass disc was bonded between two aluminium specimens in the form of a sandwich, and the resulting composite specimen broken on an Instron Universal Test Machine. Clearly in such a composite test specimen, alignment is important and there are many potential sites and modes of failure. 

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. 

This is a comparison test for ASTM D 638 on Tensile Properties of Plastics. It uses three types of specimens, Type A, where adequate sample material is available, Type B where smaller specimens are available, and Type C, which covers the tensile-adhesion properties of a cellular plastic to a substrate, as in a sandwich panel, or the bonding strength of a cellular plastic to a single substrate. 

Figure 16 shows the values for the tensile strength of the sandwich test specimen (skin component PTFE PA-6 with different contents of PTFE micropowder, core component reinforced PA-6 with 30% glass fibre). The tensile strength is mainly determined by the reinforced material, the PTFE polyamide material contributes only to a lesser degree. In a first approximation it is possible to calculate the skin content and the skin thickness. 

Fig. 2. Comparison of destructive tensile strength tests on honeycomb sandwich panels with the predicted strengths using the Fokker bond testa-. A saies of honeycomb constructions is represented, where the foil thicknesses and the cell sizes are both varied ( ), foU thickness 0.007 in. (0.177 mm), ceU size 0.125 in. (3.175 mm) ( ), foil thickness 0.003 in. (0.076 mm), cell size 0.250 in. (6.25 mm) (A), foil thickness 0.002 in. (0.05 mm), cell size 0.1875 in. (4.762 mm) (O), foil thickness 0.001 in. (0.025 mm), ceU size 0.250 in. (6.35 mm). (From R E Clemens, Paper presented at the Amoican Society for Non-destructive Testing Technical Meeting, California, February 1962)...

Tension test of flat sandwich constructions in flatwise plane. Tensile properties of adhesive bonds. 

ASTM C297 describes specimen configurations used to determine the flatwise-tensile strength of sandwich constructions in the out-of-plane orientation. This test configuration and loading are similar to that of ASTM D897. 

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