Double beam cantilever

Fig. 2. Illustrations of forces to which adhesive bonds are subjected, (a) A standard lap shear specimen where the black area shows the adhesive. The adherends are usually 25 mm wide and the lap area is 312.5 mm. The arrows show the direction of the normal apphcation of load, (b) A peel test where the loading configuration, shown by the arrows, is for a 180° peel test, (c) A double cantilever beam test specimen used in the evaluation of the resistance to crack propagation of an adhesive. The normal application of load is shown by the arrows. This load is appHed by a tensile testing machine or other...

Fracture mechanics (qv) tests are typically used for stmctural adhesives. Thus, tests such as the double cantilever beam test (Fig. 2c), in which two thick adherends joined by an adhesive are broken by cleavage, provide information relating to stmctural flaws. Results can be reported in a number of ways. The most typical uses a quantity known as the strain energy release rate, given in energy per unit area. 

These effects have been found by Creton et al. [79] who laminated sheets of incompatible polymers, PMMA and PPO, and studied the adhesion using a double cantilever beam test to evaluate fracture toughness Fc. For the original laminate Fc was only 2 J/m, but when interface reinforced with increasing amounts of a symmetrical P.M.M.A.-P.S. diblock copolymer of high degree of polymerisation (A > A e), the fracture toughness increased to around 170 J/m, and then fell to a steady value of 70 J/m (Fig. 9). 

Hashemi, S., Kinloch, A.J. and Williams, J.G. (1989). Corrections needed in double-cantilever beam tests for assessing the interlaminar failure of fiber-composites. J. Mater. Sci. Lett. 8, 125-129. 

Fig. 5.9. Load-displacement records of double-cantilever-beam tests on E-glass fiber-vinyl ester matrix composites, (a) 0.4 wt% epoxy silane (b) 0.01 wt% methacrylate silane (c) 0.4 wt% methacrylate silane (d) 1.0 wt% methacrylate silane. After Suzuki et al. (1993).

I ig. X.ll. Residual stillness a.s a funetion crack length as measured from double cantilever beam specimens after impact damage carbon fiber composites containing (O) unmodified epoxy ( ) rubber-... 

WTDCB width tapered double-cantilever-beam... 

Fiber tows are impregnated with Epon 828 (cured with m-phenylene diamine) and the prepreg cut into plies and compression molded, with 16 plies to a composite. Thin Teflon strips are inserted between plies 8 and 9 prior to molding, which initiate an interlaminar crack when the bar is loaded as a double cantilever beam. 

The mode I delamination fracture toughness is measured on flat coupons using the Double Cantilever Beam (DCB) test method. The test method utilizes a unidirectional rectangular composite specimen of uniform thickness with nonadhesive insert (as a delamination initiator) at the midplane. This test method is currently in the process of standardization by ASTM. 

BENDING OF A BEAM. The complex dynamic Young s modulus can be determined from the forced, non-resonant oscillations of a single or double cantilever beam. The apparatus considered in this paper is the Dynamic Mechanical Thermal Analyzer (DMTA) (6), manufactured by Polymer Laboratories, Inc. Figure 3 shows the experimental setup for the single cantilever measurement. A thin sample is clamped at both ends. One end is attached to a calibrated shaker through a drive shaft. 

Zehnder, A.T. and Rosakis, A.J. (1990). Dynamic Fracture Initiation and Propagation in 4340 Steel under Impact Loading, International Journal of Fracture, 43, pp. 271-285. Kalthoff, J.F., Beinert, J. and Winkler, S. (1977). Measurements of Dynamic Stress Intensity Factors for Fast Running and Arresting Cracks in Double-Cantilever-Beam Specimens. n Fast Fracture and Crack Arrest, ASTMSTP 627, pp. 161-176, Hahn, G.T. and Kanninen, M.F. (Eds.). American Society for Testing and Materials. 

ISO, Standard test method for mode I interlaminar fracture toughness, G/c, of unidirectional fibre-reinforced polymer matrix Composites. ISO 15024 2001. Blackman, B.R.K., H. Hadavinia, A.J. Kinloch, M. Paraschi and J.G, Williams, The calculation of adhesive fracture energies in mode I revisiting the tapered double cantilever beam (TDCB) test. Engineering Fracture Mechanics 2003. 70 p. 233-248. BSI, Determination of the mode I adhesive fracture energy, Gic, of structural adhesives using the double cantilever beam (DCB) and tapered double cantilever beam (TDCB) specimens. 2001. BS 7991. 

Substrates. Two commercial aluminium alloys (see Table 1), received as hot-rolled sheets (from ALCAN), were the main body-panel materials used in the current work. The thickness of the sheets varied from 1 to 3 mm for the 5754-0 alloy and from 1 to 2 mm for the 6111-T6 alloy. For the tapered double-cantilever beam (TDCB) tests, where the substrates should remain within the elastic region, a high yield strength alloy, 2014, was used throughout. The specimens were prepared and pre-treated prior to bonding using the procedures proposed by Blackman et. al. [2], The chemical compositions of the alloys employed are given in Table 1. 

Tapered Double Cantilever Beam (TDCB) Tests... 

With the initial aim of evaluating the applicability of the ISO 15024 standard for fracture toughness testing for non-unidirectional composite laminates, ESIS TC4 has conducted a number of round robin studies on cross-ply laminates with different stacking sequences. We report here the results of two test laboratories from the 3 round robin activity in which double cantilever beam (DCB) specimens made from unidirectional (0°/0°-interface) composite laminates were compared to DCB-specimens with 0°/90°- and 90790° interfaces. In the analysis, correlation with observations from the delamination growth (e.g., deviation from the mid-plane) and post-test (e.g., fracture surface) inspection was attempted. The results are compared with some results in the literature. 

The question rise whether the behaviour described can be evaluated on a fracture mechanics basis. The critical energy release rate associated with the formation of a transverse crack is technically difficult to measure. As a first approximation, it is possible to use the critical energy release rate obtained from a double cantilever beam fracture mechanics test (DCB). This test concerns the growth of a delamination between two layers (mostly oriented ai 0°) in opening mode I. Tests performed on the same carbon-polyetherimide at 0°/0° interface as in this study were reported recently [9] and gave a value of 1200 J/m. ... 

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