Standard Test Specimen

It is very desirable to fabricate a standard test specimen in the dame cycle as the part being bonded. This specimen should be designed for a test method that is indicative of the prime structural loading requirement. For example, if the critical item is normally loaded in tensile shear, the specimen should be of the lap-shear type. 

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A number of thermal stability tests arc available, some of which have developed into national (DIN) or international industrial standards (ISO). Pigments in thermoplastic systems, for instance, are studied under heat extrusion conditions [110]. The colorant to be tested, possibly together with titanium dioxide, is dispersed in the thermoplastic, using a mixer and a granulating extruder (Sec. 1.8.3). The pigmented test pellets are then fed into a screw extruder which ejects a standardized test specimen with defined dimensions [111]. Starting at the lowest possible temperature level, the extrusion temperature is increased by intervals of 10 or 20°C between samples. 

The Intermediate-Scale Calorimeter (ICAL), described in ASTM E 1623, is essentially a scaled-up version of the Cone Calorimeter. The apparatus consists of a vertical gas-fired radiant panel with a height of approximately 1.33m and width of approximately 1.54m. The standard test specimen measures lxlm, and is positioned parallel to the radiant panel. The heat flux to the specimen is preset in the range of 10-60kW/m2 by adjusting the distance to the panel. The products of pyrolysis from the specimen are ignited with hot wires located near the top and bottom of the specimen. The specimen is placed on a load cell to measure mass loss during testing. Panel and specimen are positioned beneath the ISO 9705 hood and exhaust duct. 

TESTS ON THE BONDED PRODUCT (STANDARD TEST SPECIMENS AND PROTOTYPE JOINTS)... 

A number of tests on finished bonds are useful in checking the assembly processes and in determining the adequacy of a specific adhesive for an application. These tests are generally in the form of standard test specimens or on prototype joints of the actual product. 

The cleavage test utilizes a specimen where the load is intentionally placed on one edge of the bonded area. The test method is described in ASTM D 1062. The specimen is usually loaded at a rate of 0.05 in/min until failure occurs. The failing load is reported as breaking load per unit area in pounds per square inch. A standard test specimen is illustrated in Fig. 20.9. Because cleavage test specimens involve considerable machining, peel tests are usually preferred where possible. 

The ASTM test describes in detail the apparatus for measuring compressive properties, preparation of test specimens, conditioning, and procedures. The standard test specimen is recommended to be in the form of a right cylinder or prism whose length... 

Other important features of the ASTM procedure are that the standard test specimen is a minimum of 12 in. in length, and the measurements are conducted at three temperatures, -30°F, 73°F, and 140°F (-34°C, 23°C, and 60°C), no more than 1 min after removal from the temperatnre chamber. 

Standard test specimen dimensions 80 X 10 0.5 X 4 0.2 mm. Length is20 times the thickness and width is between 10 and 25 mm. Length is 20 times the thickness and width is between 20 and 50 mm. 

The ASTM test follows the same principles but differs in certain details. The standard test specimen is based on imperial units, so that the preferred test piece is 127 mm long by 12.7 mm wide by a thickness of 12.7. 6.4, or 3.2 mm. The details of the apparatus used are the same as for the Izod test, which is covered in the nc.xi section but the form of expressing the result is different, being based on the energy normalized with respect to the length of the notch only, and not on the area behind the notch. This only serves to add to the difficulty in making comparisons between data obtained by the ASTM standard, with its dilTcrcnt test piece sizes and impact conditions, to that of the ISO standard. 

ISO 5659-2 [108] determines the optical density of smoke generated and measured in a single test chamber. The test cabinet and smoke tneasuring equipment is that of the earlier NBS test defined as ASTM E662 and BS 6401. This ISO test uses a horizontal fire model in which the standard test specimen (75 mm square) is supported on a load cell. The specimen is exposed to radiant heat from a conical radiator positioned above the specimen holder see Fig. 19. Although a range of heat flux values can be used, the standard specifies that tests should be carried out at 25 kW.nr with and without a pilot ignition flame, at 50 kW m without a pilot flame. Calculation of results is by the method defined in the earlier tests. 

ISO standards Standard test specimen dimensions 80 X 10 0.5 X 4 0.2 mm For single-phase materials... 

BS 2782 Method 335A Method 336B It tanploys cantilevCT-btaiding mode. Standard test specimen (molded) dimensions are 70 x 25.4 x 1.5 mm. A hole of diameter 2.0-2.02 mm is to be drilled centrally ... 

In the case of filled or reinforced plastics, the effect of anisotropy is usually magnified, often with significant differences in properties between flow and the transverse directions and the properties measured from large molded parts generally differ from those obtained with standard test specimens. It is, therefore, essential to evaluate the properties in tension, creep, and coefficient of linear thermal expansion, etc., in both directions for the filled or reinforced materials. 

The standard test specimen for this test consists of a strip of laminate material 152.4 mm (6 in.) long and 12.7 mm (0.5 in.) wide. A minimum of 10 samples should be prepared and all copper must be removed before testing. It is important that only samples with identical thickness and glass stack-up be tested, as this will allow a meaningful comparison of the materials in the test. The test engineer also must ensure that both the warp and fill direction of the laminate composite are measured and documented separately. 

For comparisons, the relatively small British Standard specimen was used rather than those cut by the larger ASTM tensile die. This was because of limitations in the amounts of material which were available with each mix. The British Standard test specimens were also tested by using a Monsanto Tensometer 10 tensile tester with a jaw separation rate of 50 cm/min, whereas. the special test specimens were tested with a jaw separation rate of... 

More important, however, is the performance of the adhesive in an actual joint. Standard test specimens are bonded under standard conditions and subjected to destructive tests. The load values of these tests give information on the adhesive strength between two bonded substrates. Standard destructive test methods are ... 

ISO 75 An International Organization for Standardization (ISO) standard test method for determination of heat deflection temperature (HDT) and deflection temperature under load (DTUL). HDT is a relative measure of a materials ability to perform for a short time at elevated temperatures while supporting a load. The test measures the effect of temperature on stiffiiess a standard test specimen is given a defined surface stress and the temperature is raised at a uniform rate. Alternate test methods for HDT and DTUL are DIN 53461 and ASTM D648. 

Resilience ri- zil-yan(t)s n (1824) (1) The degree to which a hody can quickly resume its original shape after removal of a deforming stress. When the body is a standard test specimen, the resilience, expressed as the percentage recovery from a stated maximum strain, may be attributed to the material from which R the specimen was made. ASTM Tests D 926 and D 945 (section 09.01) describes compression and shear tests for resilience of rubber and foam rubber. 

Lap-shear tests. The lap-shear or tensUe-shear test measures the strength of the adhesive in shear. It is the most common adhesive test because the specimens are inexpensive, easy to fabricate, and simple to test. This method is described in ASTM D 1002, and the standard test specimen is shown in Fig. 7.20a. The specimen is loaded in tension, causing the adhesive to be stressed in shear until failure occurs. Since the test calls for a sample population of five, specimens can be made and cut from large test panels, illustrated in Fig. 1.20b. 

To facilitate the inclusion of bonded joints within an engineering structure, several stages of suitability must be demonstrated. First the mechanical properties of the adhesive itself must be satisfactory and these are quantified by bulk materials tests. Once knowledge of the material itself is gained, then some idea of how well it performs in a bonded joint is required. This is most often achieved via standard test specimens such as the single or double lap joints. 

The standardized test specimens were done by the extrusion technology with simultaneous compression. The obtained composites are shown in Table 4.2. All composites were prepared in one extrusion step. 

The simplest geometric configuration of adhesively bonded structures is probably the single lap joint (SLJ), which has been widely used as a standard test specimen to calibrate adhesive properties and has been shown to be representative and challenging in identifying fundamental characteristics and key parameters in bonded lap joints. 

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