In table of physical properties of plastics, some terms are often found. Accurate understanding of meaning of these terms will help you better understand properties of plastics. Some terms related to properties of plastics are listed below. for learning you understand property sheet.
1. Tensile Strength
In a tensile test, maximum tensile stress that a sample can withstand before breaking. The result is expressed in kgf/cm2 [Pa], and area used in calculation is original cross-sectional area of the specimen at fracture site.
2. Young's modulus
Tensile modulus, that is, ratio of tensile stress to corresponding strain within Bibian limit.
3. Elasticity limit
The maximum stress that a material can withstand under stress, excluding any permanent deformation. (Note: In actual strain measurement, small loads are often used instead of zero loads as final or initial reference load.)
4. Modulus of elasticity
In limit of proportionality, ratio of stress (such as tension, compression, bending, twisting, shear, etc.) of a material to corresponding stress generated by material.
5. Impact strength
(1) The maximum ability of a material to withstand impact loads.
(2) Under impact loading, ratio of work expended in destruction of material to cross-sectional area of the sample.
6. Flexural strength
The maximum stress a material can withstand when it breaks or reaches a certain deflection under a bending load.
7. Vicat softening point test
Test method for evaluating tendency of thermoplastics to warp at high temperatures. This method consists of placing a flat needle with a given load and a cross-sectional area of 1 square millimeter on sample under condition of a constant increase in temperature, temperature at which flat needle penetrates 1 mm into sample is softening temperature of soft Wick card measured on sample .
Resistance of plastic materials to prints and scratches. (Note: According to different test methods, there are Barcol hardness, Brinell hardness, Rockwell hardness, Shore hardness, Mohs hardness, scratch hardness, Vickers (Vickers) hardness, etc.)
9. Yield strength
Stress at yield point on a stress-strain curve. Stress is force acting per unit area of an object. (Note: if area unit is calculated according to original cross-sectional area, resulting stress is engineering stress; if area unit is calculated according to cross-sectional area at time of deformation, resulting stress is true stress. Stress includes shear stress, stress tensile and compressive stress, etc.)
10. Stress cracking
Prolonged or repeated application of a load below mechanical properties of plastic results in cracks on outside or inside of plastic. (Note: The stress that causes cracking can be internal stress, external stress, or resultant force of these stresses. The rate of stress cracking depends on environment plastic is in.)
11. Internal stress
In absence of an external force, stress that occurs inside material due to improper processing, temperature changes, solvent action, and other causes.
12. Stress-strain curve
When testing a material, stress is expressed on y-axis and stress on abscissa, and a stress-strain curve is drawn.
13. Yield strength
In a stress-strain test, first point on a stress-strain curve at which stress does not increase with increasing strain. At yield point, stressed sample begins to permanently deform. The stress on sample can be any of tensile, compressive, or shear stress.
At constant stress, deformation phenomenon of material changes with time. (Note: transition warp is not included.)
15. Creeping Recovery
An area of a sample whose deformation decreases with time after load is removed.
16, fatigue limit
In a fatigue test, maximum stress when alternating stress cycle reaches infinity and specimen is still intact is called endurance limit. (Note: In fact, many plastics do not have a fatigue limit. For this reason, special number of cycles reaches 107-108 times, and stress of sample is still 50% intact, which indicates endurance limit.)
17. Fatigue life
The number of cycles of stress or strain experienced by sample under action of alternating cyclic stress or strain until failure occurs.
18 years old, hazy
Haze or opacity caused by light scattering in or on a transparent or translucent plastic. It is expressed as a percentage of direct diffused luminous flux and transmitted luminous flux.
19. Light transmission
The ratio of light flux passing through a transparent or translucent body to light flux incident on it.
The property of an object to transmit visible light and scatter less of it.
21. Oil resistance
The ability of plastics to resist dissolution, swelling, cracking, warping, or deterioration in physical properties when exposed to oil.
22. Linear expansion coefficient
Percentage change in material length per degree change in temperature.
Anisotropic materials have different physical property values in all directions. (Extruded films and sheets behave differently in winding direction than in transverse direction, and biaxially oriented films can reduce their anisotropy. Orientation can increase product strength.)
Density is weight per unit volume of a material, usually expressed in g/cm3. (During injection molding process, weight of part can be converted into density, which can be used to check quality of each molded product, or to evaluate uniformity between shape and shape during injection molding process of product. Part weight can be used as a detection point for inspection quality and process.)
Elasticity is used to describe ability of a material to return to its original shape and size after being deformed by a force. (Plastic exhibits some degree of elasticity at lower tensile strengths (≦1%). The elasticity depends on amount and type of resin and additives. Rubber and thermoplastic elastomers have a wide temperature range (50-180°F), better elasticity .)
Ductile is property whereby plastic materials cannot return to their original shape after application of a force before they are damaged by force, but this does not apply to flow and creep of materials. (Reinforced and filled resins have lower ductility and break at low loads. Thermoplastics will have better ductility at elevated temperatures. At low temperatures, plastics have lower ductility and become very brittle. Elongation is a good indicator of ductility.Thermoplastics, especially phenolic resins, have very low ductility.)
Depending on plasticity of material, stamping allows material to flow under concentrated high pressure. (Stamping can orient material molecules, increasing flexibility and tensile strength in stamping area. Semi-crystalline and crystalline resins are often stamped to form part loops. Plastic materials such as ABS, PVC, and others. Amorphous resins can also be stamped, but they usually have lower flexibility and tensile strength than engineering resins.)
28. Stress whitening effect
Because of excessive local strength of plastic products, stress whitening easily occurs, and over-yield bending without deformation, or other methods that do not cause deformation, also cause stress whitening. (Stress whitening can be used to analyze whether a product is ineffective or likely to be ineffective.)
Pliable materials can be stretched, twisted, or reshaped without compromising integrity of their physical properties. Ductility is property of a material after being stretched, usually rate at which it changes shape when heated. (Injection-molded and extruded products can be assembled with other parts or modified products while still hot due to their malleability. For example, high-filler, high-strength PVC extruded pipes during molding After pipe, expansion port for connection mechanically expanded at one end.)
Strength is ability of a material to absorb physical energy without destruction. (Typically, ductile materials have high elongation and brittle materials have low elongation.)
31. Hammer blow
This is a fast and tough impact test method carried out on a molded disc of a certain thickness. (This is best way to evaluate toughness of a material, but does not test all materials.)
32 Charpy and Izod impact strength
Charpy and Izod impact tests measure ability of a material to absorb impact energy in notched and unnotched specimens on a molded or machined specimen.
33. Impact of tension
Tensile impact test is designed to measure impact strength of plastic materials after a sudden impact under load. The test device is similar to cantilever beam impact strength test device. The impact tensile test tests tensile strength of a material on impact, and sample can be a square, round, or dumbbell-shaped test piece. (Many engineers believe that tensile impact is a better indicator of material strength in practice than Charpy and Izod impact tests.)
34 years old, brittle
Brittle means that resin does not have toughness and ductility, and also has low elongation. (Thermoset plastics, especially phenolic plastics, will exhibit brittleness unless modified with energy-absorbing additives and fillers. Factors affecting material brittleness include molecular weight and modifiers such as plasticizers, carbon black, fillers, rubber and reinforcing materials, etc. .Many base resins are inherently strong and not brittle, such as polyethylene, polypropylene, polyethylene terephthalate, nylon, polyoxymethylene, and PC.
35. Cutout Sensitivity
Notch sensitivity is a term that describes ease with which a crack propagates through a material. High elongation resin is expected to have better notch suppression capability, and notch sensitivity is reported as notched Izod impact data on material data sheet.
36, wear and friction
When mating surfaces of parts, gears, bearings, pulleys, etc. and other components move relative to each other, careful material selection is required to minimize wear. (Material suppliers often provide information on resin wear and friction when applied to various mating materials and surface finishes. To reduce contact wear on moving parts, dissimilar materials are often used. Between materials with similar properties. When friction coefficients are high, wear between dissimilar materials often higher than between different materials.In general, fiber-reinforced plastics have more wear than non-fiber-reinforced materials.Nylon has a natural lubricity and can deform under load.No wear.Plastics do not obey classical laws of friction.Before choose material for abrasive application, determine all factors in final application environment.)