Manufacturing processes shear testing

Shear strength is measured via a simple single overlap shear specimen of standard dimensions (Fig. 9). In contrast to its simple appearance, the forces in a thin-adherend shear specimen can be quite complex due to the inherent offset loading of the specimen and subsequent bending in the substrates. The single overlap shear test is anything but a pure shear test, but the configuration is easy to manufacture, simple to test and is firmly entrenched in the industry as a primary examination technique for materials qualifications, inspection and process control. 

Flat laminated panels are manufactured using fluorinated sheet substrates. The manufacturing of these test panels simulates the production process used to manufacture the fiberglass-reinforced pipes. The BS6464 test prescribes a minimum adhesive shear and peel strength of 7 MPa and 7 N/mm, respectively. Representative values for both tests are given in Tables 16.9 and 16.10 below. 

FIGURE 2.11 Rheometric steady-state test dependence of slurry viscosity rj on shear rate. The test was conducted for seven slurry samples with only subtle differences in slurry compositions and/or manufacturing processes. 

Three basic types of pressure application are used in commercial densification processes (1) Straight compression in a die (2) Extrusion through a constriction and (3) Shear of precompacted material to produce heat and flow under pressure. Approximate energy consumptions supplied by the manufacturers are compared to the laboratory tests reported here in Table IV but it must be stressed that these figures are only approximate, depending critically on type of material, size, temperature, etc. 

Various processability tests are used to predict how well a rubber compound will process. However the process" can vary greatly. Table 1 shows the diverse categories of rubber processes and some of the quality characteristics and concerns associated with each process. The natures of these processes vary because of differences in applied shear rates, temperatures, residence times, etc. Changing a given compound property can improve performance in one or more of these processes but could hurt the performance in another process. This is why it is important to look at all processes in a manufacturing operation when implementing compound changes. 

In the case of bonded composite parts, the standard process inspections are incomplete, in the sense that only lap-shear coupons are mandated. There is rarely any use of a peel test to ensure that the adhesive is stuck properly. In the author s opinion, based on years of observation of manufacturing and in-service experience, there ought to be because there is no other way of discontinuing the use of surface treatments that have been found to be inadequate. This issue is discussed by Hart-Smith (2003). 

---