Lap-shear strength measurement

Figure 28 Lap-shear strength versus ageing time in air at 177°C for Ti/Ti specimens bonded with polyimide oligomers 51. Curves (a-c) are lap-shear strength values measured at 25°C for oligomers with n = 3,2 and 1, respectively, whereas curves (a -c ) refer to lap-shear strengths measured at 177°C in the same order of molecular weights.

Figure 30 Variation of the lap-shear strength as a fnnction of the ageing time in flowing air for TU-2 titanium alloy bonded with polyimide precursors 30. Assemblies aged at 260°C lap-shear strength measnred at room temperature (a) and at 260°C (b). Assemblies aged at 300°C lap-shear strength measured at room temperature (c) and at 300°C (d).

We have also looked at the lap shear strength of selected EB-ciirable epoxy adhesives. Because the adhesives being developed were being used for both aluminum-to-aluminum and composite-to-composite applications the lap shear strengths for both adherends was measured. Aluminum adherends were T2024 phosphoric acid anodized according to ASTM 3933. The composite adherends... 

In light of these qualifications, it can only be said that the maximum measured value of 10 kg/mni seems reasonable. It also compares favorably with shear strength measurements derived from epoxy-bonded, lap-shear tests (9). 

Fixed-Position Refill. A process development matrix was obtained with a smooth cylindrical pin and shoulder profile using the fixed-position refill method (Fig. 12.28). The materials used for this study were 3.18 mm (0.13 in.) thick upper and lower sheet 2024-T3 aluminum lap joints. Characteristic measurements were made of surface indentation, effective shear area, void size, and lap-shear strength. 

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. 

Lap shear strength. Tests should be carried out over a range of temperatures, specifically including -25 °C, +20 °C and +45 °C. using bright mild steel adherends. The temperature should be measured by means of a thermocouple attached to the steel surface of the joint. Two alternative forms of lap shear joint may be employed. 

K/95% relative humidity for up to 2000 hours using lap shear (Figs. 15 and 16) and crack extension coupons (Fig. 17). The coupons were tested (lap shear) or measured (crack extension) after 1000 and 2000 hours exposure. Both PPQ and LARC-TPI do not show any shear strength degradation when... 

Frisch and Frisch also measured the critical surface tension on several epoxy/polyurethane SINs. Water-methanol and methanol-ethylene glycol mixtures were employed, using the advancing contact angle method. Interestingly, at the network compositions where the SIN samples possessed maxima in their ultimate mechanical properties, such as lap-shear strength (see Figure 7.17), the critical surface tensions exhibited pronounced minima. 

According to the final use, there exist different methods to measure the adhesive strength of polymeric materials. The island blister test and 90° peel test are particularly suited to determine the level of adhesion of very thin films in electronic applications. In the case of structural adhesives, the lap shear strength of three- or multiple-layer structures is a typical standard. 

Table 1 lists the lap shear strength values measured with Ti/Ti test specimens bonded with these thermoplastic polymers Larc-TPI, Larc TPI-ODA, Larc lA and Larc PI-SO2. The heat resistance of the four polymers in oxidative conditions was determined in an air circulating oven at 204°C for 1000 and 5000 h. 

The lap shear strength values listed in Table 3 show that Larc-IA exhibits the best adhesive properties up to 204°C before and after thermal ageing at that temperature but Larc-TPI remains better when adhesion is measured at 232°C. 

Figure 26 Lap-shear strength versus temperature measured on Al/Al assemblies bonded with (a) American Cyanamid FM 32 [73], (b) Dexter-Hysol EA 9655 and (c) Dexter-Hysol LRlOO-774 [74] BMI adhesives.

Figure 31 Variation of the lap-shear strength as a function of the ageing time in flowing air at 300°C for ZIO CNT 1810 stainless steel conpons bonded with Nolimid 380 polyimide precursor. Curves (a), (b) and (c) fit the lap-shear strength values measured at...

As bonded adhesive joints (see Figure 2) were shear-fractured in tension on an Instron tensile tester at ambient temperature and at a crosshead speed of 5 mm/min. Lap-shear strength a was calculated as fracture load divided by the contact area, averaged from at least 10 measurements. More details of the experimental procedures can be fotmd elsewhere (Boiko et al., 1997,2004). 

In order to find out as whether the lap-shear joint method may be used to measure y surface jn pigurc 7 are plotted the values of the lap-shear strength a for four symmetric polymer-polymer interfaces as a function of healing temperature at a chosen = 1 hr. As follows from Figure 7, the values of o for all the interfaces investigated decrease monotonically with a reduction in T, approaching a very small level of a (some hundredths of MPa) at r ° = 44°C (PS and PMMA), 64 = C (PET), and 90 = C (PPO), and, finally, dropping to o —>0. It means that diffusion did not occur at In terms... 

Lap Shear Strength (LSS) - A form of adhesive bond strength measured by pulling apart, in tension, two overlapped, bonded strips of material. One of the most commonly quoted mechanical properties of adhesives. Unfortunately the precise details of the adherends and conditions used for the test also have a great effect on the results obtained. 

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