Lap shear samples

Lap shear samples performed according to ASTM-D1002 or D3163. Oily metal was coated with hexadecane. All other substrates were bonded unprepared. 

Figure 5. Graph of shear strength vs. exposure time for lap shear samples constructed from untreated, alkaline cleaned or lubricated ZGUS adherends.

Corrosion Testing. Salt spray testing (ASTM-B-117-52,54) was used to determine durability of adhesive bond in corrosive environment. Lap shear samples were exposed to salt spray for 14 days and then immediately tested for lap shear strength. 

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. 

Specimen Type (3)—Lap shear samples were made by bonding the glass side of 1 in. x 1 in. pieces of silvered glass mirrors to a 1 in. x 6 in. piece of aluminized steel with a common adhesive and then bonding a second 1 in. x 6 in. piece of aluminized steel to the mirrored side with Urethanes A, B, and C. 

Shear strength—measures changes in shear strength by pulling lap shear samples on an Instron. The load at which samples pull apart is designated as the failure load. 

Fig. 32.1 Transparent lap shear sample for photoelastic stress evaluation.

For the adhesive joints which were investigated here, only some aspects wiU be discussed. The general results can be summarized as follows. A one-year exposure of bonded single lap shear samples to European and Californian ch-mates did not show any influence on the static strength of the joints. Higher temperatures (70 °C) reduced the strength by a factor between 0.25 and 0.65. 

Fractured Ti 6-4 lap shear samples were sent from the Boeing Aerospace Company and these panels were used as received. A detailed microscopic/spectroscopic study of similar samples including crack extension measurements has been reported (5). The samples used in this study are described in Table 1. It is noted that these samples are quite interesting because few bond durability studies have... 

Table 1. Description of Boeing Ti 6-4 Fractured Lap Shear Samples ...

Table 2. XPS Analysis of Fractured Boeing Ti 6-4 Lap Shear Samples Bonded with L13...

PPQ-10-46 and PPQ-10-67 - Both of these high strength (2560 and 2850 psi) lap shear samples showed minimal Ti photopeaks. The 0 Is photopeaks both at 532.4 eV are due only to the PPQ adhesive. 

A review of the XPS results in Tables 2 and 3 suggests that for the lOV chromic acid anodized Ti 6-4 adherend, the high Ti surface concentration on the L13-10-50 adhesive failure surface (APS) thermally aged for 10,000 hr is associated with the lowest strength, it is proposed that long-term thermal aging of bonded lap shear samples weakens the surface oxide. The high Ti concentration observed on the L13-10-50 adhesive failure surface (APS) results from the fracture of the surface oxide layer. 

Figure 13. XPS titanium 2p photopeak of failed lap shear sample of titanium alloy bonded with polyimide adhesive solvent cast from (a) DMAC solution and from (b) diglyme solution (22).

Figure 14. Schematic diagrams of the mode of failure of lap shear samples of galvanized steel boned with epoj based on XPS analysis (37).

Relating to the adhesive bond between the pipe and the composite, the most effective method for evaluating fliis interface is by using lap shear samples. In this application, the lap shear testing mediod uses either steel or composite adherends to test the adhesive bond. 

Another test which demonstrates the long-term performance of the adhesively bonded structure is the creep test which has been considered by Brinson et al and Rutherford and Hughes. Creep tests measure the deformation of a material under a constant load for a specified period of time. Measuring the creep resistance of adhesive systems is performed using lap shear type specimens. ASTM D2293-69 and ASTM D2294-69 use lap shear samples to determine creep behavior in compression and tension. 

T. J. St. Clair The optimized (copolymerized 65/35 BTDA/PMDA 3,3 DABP) system mentioned in the talk has been exposed to cyclic 95% relative humidity for 250 hours (at present) and the lap shear samples are essentially the same as before exposure. Testing is continuing. 

Failure of a lap shear sample with a crash-suitable adhesive... 

In the diagram in Fig. 46.21, the strength of spot welded and spot weld bonded lap shear samples with 45 mm width and 16 mm overlap plus one spot weld is shown. It shows that strength level is only determined by adhesive bonding. After the failure of the bond the spot weld can still bear additional load as was shown in the research report from Hahn and his group (Hahn and Wipiing 2007). 

Failure diagram of bonded and spot weld bonded lap shear sample... 

It is recommended to run separate lap shear samples along the whole process which can then be tested separately to have a continuous process survey. But this does not differ from the quality control system of the paint process. 

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