Лако-красочные материалы — производство

7.3.1 Long-Term Static Tests (e. g. Creep Experiments Under Dead Load) Long-term life prediction for adhesives based on laboratory tests requiring only days, weeks or months remains a demanding challenge. Testing is carried out with the intention of simulating and often accelerating the time-dependent aging effects that may happen to a joint during its lifetime. […]

Peel tests are quite similar to cleavage tests, except that at least one of the adherents is prepared from a flexible material which could be plastically deformed during the measurement. A typical peel test is illustrated in Figure 7.9; this is known as the ‘T-peel test’, and is described in ASTM D1876. Two adherents of […]

Determination of the fracture resistance of structural adhesive joints is typically tested under an applied Mode I opening load, using double cantilever beam (DCB) and tapered double cantilever beam (TDCB) specimens. The resistance to crack initiation can be determined from both a nonadhesive insert placed in the adhesive layer and from a mode I precrack. […]

Wedge and cleavage tests are common test methods applied to assess the quality of surface treatments and provide an estimate of long-term durability. Variations of the test employ thicker and longer adherents to enable longer crack growth and, therefore, more accurate fracture energy calculation and avoid plastic deformation of the adherents. 7.2.4

The true shear strength of an adhesive can be determined only if normal stresses are entirely absent. These conditions can be approached under special conditions, but not in single-lap specimens made with thin adherents, which are normally used in manufacturing and in most standard test specimens (Figure 7.3). Due to the specimen geometry, the application […]

7.2.1 Tensile Stress (e. g. Butt Joints) A tensile test ofan adhesivebond puts the adhesive in a state ofstress inwhich the bond­line is perpendicular to the direction of the force applied to the specimen. A typical sample for evaluating the tensile properties of an adhesive is shown in Figure 7.2. Figure 7.2 The basic geometry […]

The temperature resistance ofpolymer materials is often limited by thermal decom­position at elevated temperatures. However, by using a micro thermobalance the loss in weight of an adhesive sample can be monitored as a function of temperature. ASTM E2550, for example, covers a test method for the assessment of material thermal stability by determining the temperature […]

The CTE describes the temperature-dependent change in length and volume of a material. Various types of instrument can be used to measure the CTE of solid adhesives, including push-rod dilatometers or dilatometers with optical measuring devices. Within the glass transition range the CTE changes rapidly and causes additional internal stress in adhesively bonded joints, depending […]

Thermal analysis provides a rapid method for measuring transitions due to mor­phological or chemical changes (or both) in a polymer as it is heated/cooled through a specified temperature range. For dynamic mechanical thermoanalysis (DMTA; e. g. ASTM D4065), a specimen of known geometry is subjected to mechanical oscillations at fixed or natural resonant frequencies. The […]

7.1.1 Stress-Strain Analysis of Bulk Specimens Tension tests are performed on dog-bone-shaped test specimens (Figure 7.1). This geometry provides for a uniform stress and strain distribution in the central gauge section, where these values are at a maximum. Thus, the specimen extends and fails under well-defined conditions. Some flexible adhesives will sustain large extensions up […]