Double lap shear

Forced sinusoidal uniaxial tension and shear imposed by mechanical drive to tensile bar or double-lap shear specimen... 

D 3528 Test Method for Strength Properties of Double Lap Shear Adhesive Joints by... 

The measurement method described in this article is an embodiment of the non-resonance, direct-force-excitation approach that subjects a double-lap shear sample of damping polymer to force from a vibration shaker. In concept this approach can be applied irrespective of whether the material is in a rubbery, glassy, or intermediate state. Each material specimen is small in size and behaves as a damped spring over the entire frequency range. The small specimen size is in contrast with some alternate approaches in which the specimens have sufficiently large dimensions to be wave-bearing. 

The paper is presented in three parts. First, the tests employed to determine the mixed mode fracture envelope of a glass fibre reinforced epoxy composite adhesively bonded with either a brittle or a ductile adhesive are briefly described. These include mode I (DCB), and mixed mode (MMB) with various mixed mode (I/II) ratios. In the second part of the paper different structural joints will be discussed. These include single and double lap shear and L-specimens. In a recent European thematic network lap shear and double lap shear composite joints were tested, and predictions of failure load were made by different academic and industrial partners [9,10]. It was apparent that considerable differences existed between different analytical predictions and FE analyses, and correlation with tests proved complex. In particular, the progressive damage development in assemblies bonded with a ductile adhesive was not treated adequately. A more detailed study of damage mechanisms was therefore undertaken, using image analysis combined with microscopy to examine the crack tip strain fields and measure adherend displacements. This is described below and correlation is made between predicted displacements and failure loads, based on the mixed mode envelope determined previously, and measured values. 

In order to examine the application of this approach to composite assemblie.-, tests were performed on single and double lap shear specimens as shown in Table 1. Test results were compared with predictions based on reference [5]. Figure 3 shows representative results for both adhesives. 

Figure 7.6 Schematic of the double lap shear test speoimen.

Table 7.4. Bond Strength of Plasma-Treated ETFE Using a Double Lap Shear Test and Epoxy Adhesives ...

Fig. 4a and b must distort, so that the forces applied to the sample fall on the same line of action. This induces cleavage stresses in the adhesive near the bond termini. Double lap shear specimens described in ASTM D-3528 are proposed as a means of alleviating this problem (see Fig. 4c). However, based on our computer analysis and experimental studies, we feel that failure of double lap joints is still dominated by cleavage stresses [5].

Lap shear tests are close to peel tests however, this method is more quantitative in the base. Two sheets are bonded to each other by toughened adhesives (acrylic) in the test configuration and tensile tester applies load at a rate of usually 1 mm/min [96]. The lap shear specimen represents the most utilized geometry for studies of adhesive bonding because specimens as single- or double-lap shears (Fig. 8.13a, b) are easy for the measmement [97]. 

ASTM D3528-96 (2002) Standard test method for strength properties of double lap shear adhesive joints by tension loading. 

Basic metal-to-metal double-lap joint test giving the double-lap-shear strength ... 

D-3165 Strength properties of double-lap shear by tension loading of laminated assemblies. 

The key requirement for a well-configured adhesive joint (i.e. attaining optimum ultimate capacity) is to minimize any direct or induced peel stresses. Therefore, it should be arranged to transfer the applied load mainly in shear, since adhesively bonded joints can be strong in shear but are inevitably weak in peel (Hart-Smith, 2001). To this effect, peel stresses detract from the overall joint shear strength, hence were attributed as bad in the prelude to this section. Consequently, the double-lap shear bond configuration is... 

In the early 1970s, Hart-Smith (1973) managed to embrace most of the influential parameters mentioned earlier in this chapter into his renowned ID, non-linear, double lap-shear model. Addressing adhesive plasticity in his solutions is an improvement of prime significance, compared with his... 

ASTM (2004), D3528-96 (reapproved 2002), Standard test method for Strength properties of double lap shear adhesive joints by tension loading , in Annual Book of ASTM Standards, 2004 edn. West Conshohocken, PA ASTM International. 

Eawzia S, AI-Mahaidi R and Zhao X L (2006), Experimental and finite element analysis of a double lap shear connection between steel plates and CFRP , Compos Struct, 75(1-4), 156-162. 

The commercially available MTS Laboratory Automation System was the major tool used in mechanical characterization.The MTS system, as shown in Figure 7, is equipped with a computer-controlled servohydraulic capability. It is a very versatile mechanical tester which can be used to test specimens of a variety of geometries under a broad range of conditions of temperature, frequency, and strain. The double lap shear specimen used to obtain dynamic mechanical properties data is shown in Figure 8. 

Fig. 10. Double-lap shear adhesive specimen configurations (ASTM D3528).

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