Test, testing shear

Shaving products Shaw process Shear breeding Shear energy Shearlings Shearometer Shear plane Shear rate Shear stresses Shear test Shear thinning behavior Shear viscosity Sheath-core fiber... 

Table 1 contains the metal-to-metal engineering property requirements for Boeing Material Specification (BMS) 5-101, a structural film adhesive for metal to metal and honeycomb sandwich use in areas with normal temperature exposure. The requirements are dominated by shear strength tests. Shear strength is the most critical engineering property for structural adhesives, at least for the simplistic joint analysis that is commonly used for metal-to-metal secondary structure on commercial aircraft. Adhesive Joints are purposefully loaded primarily in shear as opposed to tension or peel modes as adhesives are typically stronger in shear than in Mode I (load normal to the plane of the bond) loading. 

Lap shear testing Shear can be applied in a number of ways cyclic, intermittent, static (or constant), or increasing. A simple overlap shear test is described in ASTM-D-1002. This can be illustrated again using two strong microscope slides. Here, the microscope slides are adhered in parallel to one another except offset. After the appropriate set-up time, the top and bottom of the slide combination are attached to the shear tensile-measuring device and the experiment is carried out. 

In the Jenike shear cell, the failure is forced to be in a lenticular space around the horizontal shear plane rather than throughout the whole sample and shear strains cannot therefore be determined. This disadvantage is overcome to some extent in the simple shear apparatus which confines the powder specimen in a rubber membrane or a hinged box, thereby allowing the failure to occur in the whole of the sample. As the whole thing distorts during test, shear strains can be evaluated. The shear stresses are not, however, uniformly distributed and the method has not been widely used other than in research. 

Apart from the impact and vibration tests dealt with previously, there are several other tests of friability, some of which appear in British Standards dealing with specific materials. Such tests include mixer tests, jet impingement tests, shear tests, tumbler tests and fluidized bed tests. Of these, the shear tests and tumbler tests are only considered worth mentioning here, with more details available from another BMHB publication54. 

The parameters measured arc the shear modulus and the shear strength, but not necessarily both in the same test. Shear modulus is usually measured at relatively modest strains where the stress-strain relationship is essentially linear. 

Ideally, if very soft soils are to be tested, shear strength, excess ambient pore pressure, and the bulk density (saturated density) all need to be measured in situ. If less easily disturbed marine soils are to be tested, it may be possible to both test in situ and obtain the bulk density from onboard ship measurements of good-quality cores. 

Deformation behaviour Biaxial, parallel thread tests Shear behaviour Determination of shear modulus Relaxation behaviour... 

MOR MOE Shear strength in dry test Shear strength in wet test... 

Many widely used Tests of adhesion can be applied to the rubber to metal bonds Blister test. Fracture-mechanics test specimens. Non-destructive testing of adhesively-bonded structures. Peel tests. Shear tests. Tensile tests and Wedge test. This particular article is concerned with those aspects that are of practical concern in the rubber-processing industry. 

Specific tests of adhesion are described in more detail under the following articles Blister test, Climbing drum peel test, Fracture mechanics. Napkin ring test. Peel tests. Rubber to metal bonding - testing. Shear tests. Tensile tests. Wedge test and in Refs. [1-5] see also Standards for adhesives and adhesion and Appendix. 

The industry has established three standard test shear rates based on the shear rates generated from the 100,... 

In plastics testing, shear strength (ASTM D732) is determined with a 2-in.-diameter or 2-in.-square test specimen, ranging in thickness from 0.005 to 0.500 in. placed in a punch type shear fixture. Pressure is applied to the punch at the rate of 0.005 in./min until the moving part of the sample clears the stationary portion. The force divided by the area sheared determines the shear strength. 

Shear properties of structural adhesives by the modified rail test. Shear strength and shear modulus of structural adhesives. 

As with other pressure-sensitive adhesive tests, the temperature is an important variable and tests are typically carried out at room temperature. A variation on this method is the SAFT test (shear-adhesion-failure temperature) in which the test apparatus is placed in an oven where the temperature is set to rise at 4.5°C/min. The temperature at which the tape fails is recorded as the SAFT value. 

Rheological characterization of pharmaceutical powders using tap testing, shear cell and mercury porosimeter. Int. J. Pharm., 189, 91-103. 

Flow Curves. In this type of testing, shear stress or shear rate is changed as a function of time and resulting shear rate or shear stress is measured. This type of test is generally used to survey flow behavior over one to two orders of magnitude of shear rate range. Thixotropic behavior of pastes can be determined from the hysteresis in shear stress-shear rate plots. There are several phenomenological models available to curve-fit the experimental data. Flow curves for various thick-film pastes are shown in Fig. 8.81. 

Young s Modulus at very small deformations Young s Modulus at 50 /o of the failure stress Friction Ratio CPT test Shear Modulus... 

Cone penetration test Dilatometer test Shear wave velocity Small strain shear modulus Standard penetration test... 

As with tensile tests, shear tests can be divided into bulk and joint tests. The adhesive displacement in joint tests is very small and it is therefore more difficult to measure accurately. Bulk specimens give more accurate results because the gauge length is higher. However, it can be argued that the size and thickness of the specimens used are not representative of the adhesive properties in a joint. The National Physical Laboratory and other British laboratories (Dean et al. 1996) have carried out an extensive theoretical and experimental study on various shear test methods. Many of their findings are well accepted by the adhesive community and are also presented here. 

Sealants work under the same principles as adhesives, hut their main objectives are to bond two surfaces and to fill the gap between them forming a barrier or protective layer against water, air, and so on. Elastomeric foam adhesives are another type of adhesive, but share a common feature that such adhesives are often used in thick film conditions. Here, the tensile test, shear test, and tensile adhesion tests relevant to such materials are explained. 

Since creep is considered as a key weaknesses of pressure sensitive adhesives, various specific test methods and standards have been developed to evaluate the creep resistance of pressure sensitive adhesives like, for example, in the European Standard EN 1943 ( Self adhesive tapes-Measurement of static shear adhesion ), FINAT (Federation Internationale des Fabricants et Transformateurs d Adhesives et ThermocoUants sur Papier et autres Supports), test method FTM 8 (Resistance to shear from a standard surface), or the Pressure Sensitive Tape Councils test method PSTC 107 (International Standard for Shear Adhesion of Pressure Sensitive Tape) by either monitoring the time- and load-dependent displacement of an adhesive specimen under shear load or simply recording the time to failure. The result of the so called SAFT-test ( Shear Adhesion Failure Temperature ) indicates the temperature at which a sample that has been subjected to an environment with steadily rising temperature under static shear load has failed. 

In testing shear resistance, one always looks for cohesive failure. As the temperature increases, shear resistance goes down as the adhesive mass softens. This reduction in shear resistance will be fairly slow and steady, to the point where the mass is so soft that it will not support a load for any appreciable time. 

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