Plastics, mechanical properties tests

Mechanical properties of plastics can be determined by short, single-point quaUty control tests and longer, generally multipoint or multiple condition procedures that relate to fundamental polymer properties. Single-point tests iaclude tensile, compressive, flexural, shear, and impact properties of plastics creep, heat aging, creep mpture, and environmental stress-crackiag tests usually result ia multipoint curves or tables for comparison of the original response to post-exposure response. 

Strength and Stiffness. Thermoplastic materials are viscoelastic which means that their mechanical properties reflect the characteristics of both viscous liquids and elastic solids. Thus when a thermoplastic is stressed it responds by exhibiting viscous flow (which dissipates energy) and by elastic displacement (which stores energy). The properties of viscoelastic materials are time, temperature and strain rate dependent. Nevertheless the conventional stress-strain test is frequently used to describe the (short-term) mechanical properties of plastics. It must be remembered, however, that as described in detail in Chapter 2 the information obtained from such tests may only be used for an initial sorting of materials. It is not suitable, or intended, to provide design data which must usually be obtained from long term tests. 

The mechanical properties of plastics enable them to perform in a wide variety of end uses and environments, often at lower cost than other design materials such as metal or wood. This section reviews the static property tests. Chapter 5 provides more information on the meaning of these type data. 

Torsion property As noted, the shear modulus is usually obtained by using pendulum and oscillatory rheometer techniques. The torsional pendulum (ASTM D 2236 Dynamic Mechanical Properties of Plastics by Means of a Torsional Pendulum Test Procedure) is a popular test, since it is applicable to virtually all plastics and uses a simple specimen readily fabricated by all commercial processes or easily cut from fabricated products. 

Mechanical properties testing, for plastics, 19 579-582. See also Mechanical testing... 

ASTM D 5026-95a, Standard Test Method for Measuring the Dynamic Mechanical Properties of Plastics in Tension, ASTM, West Conshohocken, PA, 1997. 

Note of the author This procedure was one of the most widely used of the mechanical property tests for wood-plastic composite (WPC) materials, as the specimen geometry is very simple as well as the testing equipment. However, it became more and more obvious that material properties, tested by this method, were not necessarily corresponding to the product properties, such as composite deck board. 

Mechanical Properties 1. Plastic properties 2. Tests on the failed material, e.g., tensile and environmental stress crack resistance (ESC)... 

Evaluation of chemical resistance may establish the potential for extraction of plasticizer incorporated in the material as well as an effect of plasticizer on durability of tested material. The standard contains information on testing chemical resistance with 50 test liquids using two methods immersion test and test under mechanical stress. The list of test liquids includes white oil which may be regarded as the only example of plasticizer among test liquids. Samples of known dimensions and weights are immersed in selected liquids for 168 h at room temperature. Containers are stirred every 24 h. Changes in appearance are recorded and samples can be subjected to mechanical property testing. Tensile properties of immersed samples are most frequently compared with control samples but other mechanical tests may also be used. 

Solid-state polymerization of crystalline monomer without any intermediate loss of order. The topotactic oligomers have been produced, but the order is lost as the polymerization progresses beyond a low degree of polymerization. Test equipment used for determining the dynamic mechanical properties of plastics. 

Dynamic mechanical analyzer n. An instrument that can test in an oscillating-flexural mode over a range of temperature and frequency to provide estimates of the real , i.e., in-phase, and imaginary , i.e., out-of-phase parts of the complex modulus. The real part is the elastic component, the imaginary part is the loss component. The square root of the sum of their squares is the complex modulus. With polymers, the components and the modulus are usually dependent on both temperature and frequency. ASTM D 4065 spells out the standard practice for reporting dynamic mechanical properties of plastics. An example of a DMA thermogram of different Perkin-Elmer Inc., manufactures the Diamond DMA instrument. Polymer films is shown. Sepe MP (1998) Dynamic mechanical analysis. Plastics Design Library, Norwich, New York. 

Mechanical property n. Any property of a material that defines its response to a particular mode of stress or strain. Such properties include elastic moduli, strength, and ultimate strain in several modes, impact strength, abrasion resistance, creep, ductility, coefficient of friction, hardness, cychc fatigue strength, tear strength, and ma-chinability. Many ASTM tests in Section 08 are devoted to the mechanical properties of plastics. 

ASTM D5023-01 (ISO 6721-3), Standard Test Measuring the Dynamic Mechanical Properties of Plastics in Flexure Using Three Point Bendingf ... 

Standard Test Method for Dynamic Mechanical Properties of Plastics by Metals of a Torsional Pendulum... 

Even though torsion pendulum tests run at elevated temperatures provide very useful information regarding the dynamic mechanical properties of plastics, one must not forget that it is, nevertheless, a short-term test. The data obtained from creep modulus and creep rupture tests conducted at elevated temperatures must be relied on for long-term effects. 

Test method for dynamic mechanical properties of plastics by means of a torsional pendulum Practice for determining resistance of synthetic polymer material to fungi. Practice for determining resistance of plastics to bacteria... 

The radiation and temperature dependent mechanical properties of viscoelastic materials (modulus and loss) are of great interest throughout the plastics, polymer, and rubber from initial design to routine production. There are a number of laboratory research instruments are available to determine these properties. All these hardness tests conducted on polymeric materials involve the penetration of the sample under consideration by loaded spheres or other geometric shapes [1]. Most of these tests are to some extent arbitrary because the penetration of an indenter into viscoelastic material increases with time. For example, standard durometer test (the "Shore A") is widely used to measure the static "hardness" or resistance to indentation. However, it does not measure basic material properties, and its results depend on the specimen geometry (it is difficult to make available the identity of the initial position of the devices on cylinder or spherical surfaces while measuring) and test conditions, and some arbitrary time must be selected to compare different materials. 

---