Double overlap shear

Fig. 1, Schematic of commonly u.sed methods for testing the strength of adhesive joints, (a) Peel test. Note that the peel angle can be changed depending on the test requirements, (b) Double overlap shear test. In this test, the failure is predominantly mode II. (c) Single overlap shear test. In this test the failure mode is mixture of mode I and mode II. (d) Blister test.

Shear strength 20 °C To survive 10 double overlap joint... 

An alternative form of double overlap joint, which more closely reflects shear stress distributions in service, is shown in Fig. A.7. The dimensions / and d are selected so that the... 

Fatigue test. Fatigue tests should be carried out at a constant frequency between 1 and 25 Hz, with a sine wave form and using TAST or double overlap joints as described above. The joints should be capable of surviving, without failure, 10 cycles of a mean shear stress range between 1.0 and 10 MN at 20 °C for TAST joints... 

Notes Tube shear strength to Boeing BMS 5-90F using 2.54mm film. Notes Tensile lap shear strength and Service temperature - ASTM D 1002, Tensile properties - ASTM D 638. x (wet) double overlap coupon. ... 

The electroviscous effect present with solid particles suspended in ionic liquids, to increase the viscosity over that of the bulk liquid. The primary effect caused by the shear field distorting the electrical double layer surrounding the solid particles in suspension. The secondary effect results from the overlap of the electrical double layers of neighboring particles. The tertiary effect arises from changes in size and shape of the particles caused by the shear field. The primary electroviscous effect has been the subject of much study and has been shown to depend on (a) the size of the Debye length of the electrical double layer compared to the size of the suspended particle (b) the potential at the slipping plane between the particle and the bulk fluid (c) the Peclet number, i.e., diffusive to hydrodynamic forces (d) the Hartmarm number, i.e. electrical to hydrodynamic forces and (e) variations in the Stern layer around the particle (Garcia-Salinas et al. 2000). 

Two other variations are used to avoid the bending forces that occur with simple ASTM D 1002 specimens the laminated lap shear specimen (ASTM D 3165) shown in Fig. 20.6a and the double-lap specimen (ASTM D 3528) shown in Fig. 20.6b. These specimens minimize the joint eccentricity and provide higher strength values than does the singleoverlap specimen. For the specimen in Fig. 20.6a, the overlap joint can be made from saw cuts in the top and bottom substrates of a bonded laminate. This process negates the effects of extruded adhesive at the edges of the lap and the sheared edge of the standard type of lap shear specimen. As a result, the chances of deformation and uneven surface preparation are lessened. 

Monodisperse melts appear to exhibit a plateau region in the stress vs shear rate flow curve [51,62,65]. The capillary flow behavior actually closely resembles the oscillatory shear behavior in the sense that the flow curve essentially overlaps on the absolute value of complex modulus G vs the oscillation frequency (0 [62]. Thus.it appears that the transition-like capillary flow behavior of highly entangled monodisperse melts reflects constitutive bulk properties of the melts and is not interfacial in origin. It remains to be explored whether this plateau indeed manifests a real constitutive instability, i.e., whether it is double-valued. 

The above-described thickeners produce a three-dimensional gel network by the overlap of the polymer coils of H EC or the double helices of xanthan gum. Apart from their effect in reducing creaming and sedimentation by producing a high residual viscosity (at low shear rates), these polymers will also prevent the... 

Electroviscous Effect Any influence of electric double layer(s) on the flow properties of a fluid. The primary electroviscous effect refers to an increase in apparent viscosity when a dispersion of charged colloidal species is sheared. The secondary electroviscous effect refers to the increase in viscosity of a dispersion of charged colloidal species that is caused by their mutual electrostatic repulsion (overlapping of electric double layers). An example of the tertiary electroviscous effect would be for polyelectrolytes in solution where changes in polyelectrolyte molecule conformations and their associated effect on solution apparent viscosity occur. 

A theoretical explanation for the increase of the viscosity t) could be found in the so-called electroviscous effect. It is well known that an electrolyte solution streaming between two charged walls shows an increase of the apparent shear viscosity. Assuming that the results obtained for plane parallel channels in a steady state by Levine et al. " may be used for the film situation, it was found that a maximum increase of about 20% can be expected for the viscosity of the solution inside the film compared to the bulk value. This electroviscous effect is expected to be important only in equilibrium films where an overlap of the electrical double layers occurs but nevertheless this phenomenon cannot explain the full discrepancy between theory and experiment. 

A coarse calibration of the higher frequency loss permittivity data becomes possible by using the overlap with the loss shear modulus values. It seems reasonable to conclude that the loss shear modulus values would reach 5 x 10 Pa or more near 3 kHz. The comparison also suggests that the intensity of the peak in Figure 1A would almost double on continuing from 20 to 40 C. It should also be appreciated that the composition of the elastic protein-based polymer can be chosen such that the temperature interval is below 5 C in which case the intense absorption would exist at temperatures above 5 C. 

The generation of a stable and controllable fluid flow in microfluidic devices is a major issue, and a lot of research work has been put into optimizing the flow driving methods. Not only conventional methods (derived from macroscopic applications) like pressure-driven and electroosmotic flows have been scaled down, but also novel methods like shear-driven flows (SDF) have been introduced. There are several problems associated with the conventional flow driving methods pressure-driven flows suffer from pressure drop limitations, while electroosmotic flows suffer from Joule heating, fluctuations of flow velocity, and double-layer overlap [1]. Therefore, other approaches to evade these problems and limitations have been proposed (centrifugal forces, magnetohydrodynamic forces, etc.). 

Single- and double-lap and single- and double-strap joints have stress concentrations at the ends of the overlap when loaded with in-plane loads. These are the most probable locations for the failure initiation. A t3rpical shear stress distribution is shown in Figure 5.27. 

The temporary maximum joint resistance (bond shear strength) can be calculated by assuming that the adhesive failure shear strain is encountered at the end of the overlap. For a double-lap configuration the maximum load is specified by the lesser of the values given by the following pair of equations (reference 5.30) ... 

In a variant the rotating discs are omitted and the circular filter elements themselves, which are double-sided and mounted on a hollow shaft, are caused to rotate. With some types a second, counter-rotating, set of filter elements overlaps the peripheries of the first set to further enhance shear at the... 

Tapered butt joints and double scarf-lap joints also permit bonding and provide maximum tensile and shear strength. Overlap joints are recommended for bonding cylindrical parts ... 

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