Tests impact

Impact test can be used to evaluate the fracture characteristics of polyethylene composites. In this test, pendulum with a massive striking edge is allowed to hit the specimen. The mass and the drop height determine the potential energy of the hammer. The impact test can be carried out by using ASTM D-256 method. 

Breakdown of particles on impact can be tested either on single particles or on a quantity of the bulk solid, and the result is a measure of particle friability. The available tests have been well reviewed in the recent attrition report by the Board54 and only a mention of the main methods is given here. 

Leaving aside single particle impact tests which fall into section 6.1, the most common type of multiparticle impact tests are drop shatter tests in which a specified quantity of the test material is dropped through a specified height onto a hard surface or into a container. National and international standards exist on drop shatter tests for coke and coal and similar tests are also applied to iron ores and sinters. Drop shatter tests are in general used on coarser solids than those within the scope of this guide the fine fraction is in fact often removed from the bulk material before the test. 

With harder materials like aggregates, sands and fillers, an impact test machine is used59 which uses a 14 kg hammer to drop from a height of 380 mm onto a specified quantity of the sample in a cup. The amount of fines produced by the impact is an indication of the shatter resistance. 

Plastics products are most likely to fail in a brittle manner under impact conditions, both due to strain rate effects and because large forces can be generated by low energy impacts on stiff structures. A variety of impact tests are used. Usually a weight falls from a height of the order of Im to hit the test specimen with a velocity of about 5ms . This simulates the strain rates that occur when a product is dropped about a metre, but not the higher strain rates in vehicle collisions or ballistic impacts. The uses and limitations of three types of impact tests will be discussed. 

The Izod test is a variant of the notched bending test. A swinging pendulum hits a clamped bar (Fig. 9.16) and loses kinetic energy. The bar has a width of 12.5 mm and a thickness representative of the plastic product considered. The 2.5 mm deep, 45° notch has a tip radius of 0.25 mm. Section 9.3.2 showed that the tensile stress in the yielded zone at the notch tip can exceed the uniaxial tension yield stress by up to 118%. It is common to use 3.2 mm thick specimens, which restricts the value of the data to products of similar thickness. The lower half of the bar is clamped in vice, and the upper part is struck 22 mm above the notch by the pendulum. The results can be quoted as the absorbed energy divided by the specimen thickness, in Jm , or as the absorbed energy divided by the area of one fracture surface, in J m .  

Charpy specimens are also notched in the centre, but the bar is freely supported at the ends, and struck in the centre of the face opposite the 

Variation of the energy absorbed in a Charpy impact test with the radius of the notch tip in 3 mm thick bars (from Ogorkiewicz, R. M., Ed, Thermoplastics—Properties and Design, Wiley, 1974). 

The 5 ms failure time in a Charpy impact test is 2000 times smaller than the 10 s failure time in a slow bend test. This increases the value of the yield stress, without necessarily increasing the stress for crazing. For some polymer/temperature combinations there may be a changeover from yielding to crazing and plane strain fracture. 

---

Component Composition, wt % Heat of reaction, kj/g" Gas volume, cmVg Relative brisance, % TNT Ignition temp, °C Impact test, % TNT... 

ASTM E23-93, "Notched Bar Impact Testing of MetaUic Materials," Annual Book of ASTM Standards, ASTM Puhhcations, Philadelphia, 1993. ASTM D256-92, "Impact Resistance of Plastics and Electrical Materials," Annual Book of ASTM Standards, ASTM Puhhcations, Philadelphia, 1993. A. N. Atiuri and T. Nishioka, Int. / fract. 27, 245 (1985). 

Subsequent to processing, an inspection is made for incomplete bonding, inside dirt, and glass quaUty. In the case of windshields, rigid optical standards must be met, and these must be evaluated for the completed windshield. Extensive test requirements are described in the appropriate codes (11,12,15,18—24), and they include light stabiUty, resistance to optical distortion, humidity, boil test, abrasion resistance, and assorted impact tests. 

Testing of Painted Products. The enhancement of paint adhesion is one of the principal functions of conversion coating (20—22). A group of tests based on product deformation is used to test the painted product. The appHance and cod-coating industries use the mandrel bend, the cross-hatch adhesion test, and the direct and reverse impact tests. Adhesion after a water soak is judged using a cross-hatch test performed on the exposed surface. 

Four modes of characterization are of interest chemical analyses, ie, quaUtative and quantitative analyses of all components mechanical characterization, ie, tensile and impact testing morphology of the mbber phase and rheology at a range of shear rates. Other properties measured are stress crack resistance, heat distortion temperatures, flammabiUty, creep, etc, depending on the particular appHcation (239). 

Impact resistance is determined usiag flyer plate impact tests, long rod impact tests, Hopkinson bar tests (50), and the Hquid jet technique (51). Impact damage resistance is often quantified by measuring the postimpact strength of the ceramic. 

Certain forms of this material, as stated in Table 10-57, must be impact-tested to qualify for service below -29 C (-20 F). Alternatively, if provisions for impact testing are included in the material specification as supplementary requirements and are invoked, the material may be used down to the temperature at which die test was conducted in accordance with the specification. 

The minimum temperahire shown is tliat design minimum temperature for which the material is normally suitable without impact testing otlier tlian that required by the material specification. However, the use of a material at a design minimum temperature below -29 C (-20 F) is established by rides elsewhere in the code, including any necessary impact-test requirements. 

This material when used below -29 C (-20 F) requires impact testing if the carbon content is above 0.10 percent. 

AU other carbon steel, low-intermediate, and high-aUoy steels, ferritic steels Base metal Deposited weld metal and heat-affected zone (See Note 1) 2. Except when conchtions conform to Note 2, the material shall be heat-treated to control its microstructure by a method appropriate to the material as outlined in the specification applicable to the product form and then impact-tested. (See Note 1.) Deposited weld metal and heat-affected zone shall be impact-tested. 

Austenitic stainless steel 3(3. If (1) the carbon content by analysis is greater than 0.10 percent or (2) the material is not in the solution-heat-treated conchtion, then impact testing is required for design temperatures below-29 C (-20 F). See Note 2. ib. When materials are fabricated or assembled by wel(hng, the deposited weld metal shall be impact-tested for design temperature below —29 C (—20 F) unless cou(htious conform to Note 2. 3. The material shall be impact-tested. See Note 2. 

Austenitic ductile iron, ASTM A571 4(3. No ad(htional requirements. 4b. Wel(hng not permitted. 4. The material shall be impact-tested. This material shall not be used at design minimum temperatures lower than —196 C (—320 F). Wel(hug is not permitted. 

Impact testing is not required if the design temperature is helow —29 C (—20 F) hut at or above —46 C (—50 F) and the maximum operating pressure of the fabricated or assembled components will not exceed 25 percent of the maximum allowable design pressure at ambient temperature and the combined longitudinal stress due to pressure, deadweight, and displacement strain (see Par. 319.2.1) does not exceed 41 MPa (6000 Ibfiin ). 

Impact Testing Materials conforming to ASTM specifications listed in the code may generally be used at temperatures down to the lowest temperature listed for that material in the stress table without additional testing. When welding or other operations are performed on these materi s, additional low-temperature toughness tests may be reqiiired. The code requirements are listed in Table 10-57. 

Fabrication tolerances are covered in this subsection. The tolerances permitted for shells for external pressure are much closer than those for internal pressure because the stability of the structure is dependent on the symmetry. Other paragraphs cover repair of defects during fabrication, material identification, heat treatment, and impact testing. 

Low-temperature service is defined as being below—29°C (—20°F), and impact testing of many materials is required. The code is restrictive in the type or welding permitted. 

Figure 9.20. Experimental setup for symmetric plate impact test.

Figure 9.21. Comparison of calculational and experimental results for plate impact test.

Figure 9.20 shows the setup for a symmetric plate impact test. The projectile here has a facing plate of ceramic and is backed with a low-density foam, for support of the ceramic during launch. The facing plate of the target is also made of ceramic. The lithium fluoride slab, which backs the target sample, serves as a window for the laser velocity interferometer (VISAR) that measures the time-resolved particle velocity at the sample/window interface. 

Temper 650/1100°F Very low impact test Heat treated alloy Heat treated alloy Slow cooling Add about. 50%... 

It is probably most useful to consider toughness as a property of a plastics part under some specified conditions of service. Whilst it is possible to devise impact tests and to rank a series of plastics materials according to the results obtained in such tests it remains almost impossible to use such tests to try to predict whether or not an article made from a specific material will or will not be satisfactory in service. 

Impact tests are, however, used to try to compare the impact strength of different materials. Of these tests four require specific mention. These are the Izod test, the Charpy test, the falling weight tests and the tensile impact test. 

Other impact tests widely used are the falling weight tests where a weight is allowed to fall onto a supported flat or domed surface and tensile impact tests in which a sample is subjected to a sudden shock in tension. Whilst the... 

VINCENT, p. I., Impact Tests and Service Performance of Plastics, Plastics Institute, London (1971)... 

---