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(Collection) plastic performance terminology!
In the plastic properties table, often encounter some terms, accurate understanding of the meaning of these terms, will help to better grasp the properties of plastics, the following list of some plastic properties terms, teach you to understand the physical properties table.
The tensile strength
In a tensile test, the maximum tensile stress applied to a specimen up to the point of fracture.
The results are expressed in kilogram force/cm 2[Pa], and the area used in calculation is the original cross-sectional area of the sample at the fracture.
Young's modulus
The modulus of elasticity under tension is the ratio of the tensile stress to the corresponding strain within the limit of comparison.
Elastic limit
The maximum stress that a material can withstand without leaving any permanent deformation.
(Note: In actual strain measurement, a small load is often used rather than zero load as the final or initial reference load.)
Modulus of elasticity
The ratio of the stress (e.g. tension, compression, bending, twisting, shearing, etc.) applied to the material to the corresponding strain produced by the material within the proportional limit.
The impact strength
(1) the maximum capacity of the material to bear the impact load.
(2) Under the impact load, the ratio of the work consumed when the material is destroyed to the cross-sectional area of the sample.
The bending strength
The maximum stress that can be sustained when a material breaks under a bending load or reaches a specified deflection.
Vica softening point test
A test method for evaluating the deformation tendency of thermoplastics at high temperature.
This method is under the condition of constant temperature rise, with a specified load, cross-sectional area of 1 square millimeter flat top needle on the sample, when the flat top needle into the sample 1 millimeter temperature is the degree of the sample measured by the Vica soft card softening temperature.
hardness
Resistance of plastic materials to imprint and scratch.
(Note: according to different test methods, there are Barcol hardness, Brinell hardness, Rockwell hardness, Shore hardness, Mohs hardness, Scratch hardness and Vickers hardness, etc.)
Yield stress
The stress at the yield point on the stress-strain curve.
Stress, the force acting on unit area of an object.
(Note: If the unit area is calculated according to the original cross-sectional area, the stress obtained is the engineering stress;
If the unit area is calculated according to the cross-sectional area at the moment of deformation, the stress obtained is true stress.
The stress is different from shear stress, tensile stress and compressive stress.
Stress cracking
Long time or repeated application of stress lower than the mechanical properties of plastics caused by plastic external or internal crack phenomenon.
(Note: The stress that causes cracking can be internal or external stress, or a combination of these stresses. The rate of stress cracking varies with the environment in which the plastic is placed.)
Internal stress
In the absence of external force, the material due to improper processing and molding, temperature changes, solvent action and other causes of the stress.
Stress-strain curve
A stress-strain curve in material testing in which stress is indicated on the vertical axis and strain is indicated on the abscissa.
The yield point
In a stress-strain test, the first point on the stress-strain curve at which stress does not increase with strain.
At the yield point, the specimen under stress begins to undergo permanent deformation.
The stress to which the specimen is subjected may be any of tensile, compression or shearing stresses.
creep
The change of material strain with time under constant stress.
(Note: Instant strain is not included)
Creep recovery
The part of a specimen whose deformation decreases with time after the load is removed.
Fatigue limit
In the fatigue test, the maximum stress when the stress cycle is infinite and the sample is still not damaged is called the fatigue limit.
(Note: many plastics in fact do not have a fatigue limit, for this purpose, the special use of 107 to 108 cycles and the specimen still 50% of the stress without damage to represent the fatigue limit)
The fatigue life
The number of cycles of stress or strain subjected to alternating cyclic stress or strain until failure occurs.
The fog degree
The misty or cloudy appearance of the interior or surface of a transparent or translucent plastic caused by light scattering.
It is expressed as a percentage of the forward scattered luminous flux and the transmitted flux.
Light transmittance
The percentage of the luminous flux passing through a transparent or translucent body and its incident luminous flux.
transparency
The property of an object that transmits visible light and scatters less.
Oil resistance
The ability of plastics to resist dissolution, swelling, cracking, deformation or physical degradation caused by oils.
Coefficient of linear expansion
Percentage change in material length for 1 degree change in temperature.
The anisotropic
Anisotropic materials have different physical property values in all directions.
Extruded films and sheets behave differently in the coiling direction than in the transverse direction, and the anisotropy can be reduced by biaxial orientation of the films.
The strength of the product can be improved by orientation.)
The density of
Density is the weight of a material per unit volume, usually expressed in g/cm3.
During the injection molding process, the weight of parts can be converted to density, which can be used to check the quality of each molded product, or to evaluate the uniformity between molds during the injection molding process.
Part weight can be used as a checkpoint for quality and process control.
The elastic
Elasticity is a term used to describe the ability of a material to return to its original shape and size after being deformed under stress.
(Plastics show certain elasticity at low tensile strength (≦1%).
Elasticity depends on the amount and type of resin and additive.
Rubber and thermoplastic elastomers have good elasticity over a wide temperature range (50-180F)
The plastic
Plastic material in the force has not reached the destruction before, after the release of force can not return to the original shape of the property called plasticity, but this does not refer to the flow of materials and creep.
Reinforced and filled resins have low plasticity and will break at low stresses.
Thermoplastics become more plastic as the temperature increases.
Plastics have low ductility and become very brittle at low temperatures.
Elongation is a good measure of plasticity.
Thermosetting plastics, especially phenolic resins, have very low plasticity.
Stamping forming
Depending on the plasticity of the material, stamping can cause the material to flow under concentrated high pressure.
Stamping can Orient the material's molecules, increasing flexibility and tearing strength in the area of the stamping.
Semi-crystalline and crystalline resins are often pressed to form the hinges of parts.
Plastic materials such as ABS, PVC, and other amorphous resins can also be stamped, but their flexibility and tear strength are usually lower than engineering resins.
Stress whitening effect
Because the local force of plastic products is too large, it is easy to produce stress whitening. Under the condition of no deformation, bending to exceed its yield point or other methods that do not lead to its deformation will also produce stress whitening.
Stress whitening can be used to analyze whether or not a product has failed or may fail.
ductility
A malleable material can be stretched, rolled or stretched into another shape without destroying the integrity of its physical properties.
Ductility is the property of a material when it is stretched, usually the rate at which it changes its deformation when it is heated.
Injection and extrusion products use their ductility to assemble or modify products with other parts while they are still very hot.
Such as the extrusion of high hardness and high filling PVC pipe, after forming the pipe, on one end of the mechanical expansion of a connection with the expansion mouth)
toughness
Toughness is the ability of a material to absorb physical energy without failure.
(Usually ductile materials have high elongation and brittle materials have low elongation)
Drop hammer impact
This is a fast, hard impact test done on a molded disk of a specific thickness.
(This is one of the best ways to assess the toughness of a material, but it can't test everything.)
Impact strength of simply supported beam and cantilever beam
The impact strength test of simply supported and cantilever beams is to measure the ability of a material to absorb the impact energy by notched and unnotched splines on a molded or machined sample.
Tensile impact
Tension impact is to measure the toughness of plastic materials under the stress state after sudden impact, the test device is similar to the cantilever impact strength of the test instrument.
The tensile impact test examines the impact tearing strength of the material. The sample may be a square, round, or dumbbell shaped test spline.
(Many engineers believe that tensile impact is a better indicator of the actual toughness of the material than simply supported and cantilever impact tests.)
brittle
Brittleness means that the resin has no toughness and ductility, and has low elongation properties.
(Thermosetting plastics, especially phenolics, exhibit brittleness if they are not modified with energy-absorbing additives and fillers.
The factors that affect the brittleness of materials are molecular weight and modifier, such as plasticizer, carbon black, filler, rubber and reinforcing material.
Many of the substrate resins themselves are tough without brittleness, such as PE, PP, PET, nylon, polyformaldehyde and PC.
Notch sensitivity
Notch sensitivity is the term used to describe the ease with which cracks can propagate along a material.
It is suggested that the resin with high elongation has a better ability to suppress the notch. The notch sensitivity is listed in the data sheet of the material as the impact strength of the notched cantilever beam.
lubricity
Thermoplastics have self-lubricating properties, indicating the properties of materials to bear loads in relative motion.
(Greasily lubricated plastics have a small coefficient of friction in both motion and static tests)
Wear and friction
When the contact surfaces of parts, gears, bearings, pulleys, etc. move relative to other components, careful selection of materials is required to reduce wear.
Material suppliers usually provide information on wear and friction of resins when applied to different mating materials and surface finishes.
In order to reduce the contact wear of parts in motion, dissimilar materials are often used.
High friction rates between materials with similar properties often result in higher wear than between different materials.
In general, fiber-reinforced plastics have greater wear than non-fiber-reinforced materials. Nylon has a natural lubricity and can deform under load without wear.
Plastics do not obey the classical laws of friction.
Before selecting a material for wear application, determine all the factors in the final application environment.
shrinkage
Thermoplastics become a fluid when heated and expand. When cooled, they solidify from their initial molten state and contract. This change in volume and density from liquid to solid is called material or mold shrinkage.
Shrink rates usually provided by suppliers are those measured under optimal injection molding conditions.
This value is an average and is subject to change according to injection molding conditions and orientation.
The shrinkage rate of amorphous resin is smaller than that of crystalline and engineering resin.
During injection molding, the shrinkage is slightly higher in the lateral direction and at a 90° Angle to the direction of flow.
If the thickness of the cross section increases, the shrinkage of the die and material will increase, and even higher in the transverse direction perpendicular to the direction of flow.
The mold designer must adjust the dimensions within the mold cavity for dimensions that cannot be controlled by the mold.
The shrinkage rate of each material, the position of the gate on the part, and the filling position of the material must be adjusted according to the thickness of the section.
Injection molding conditions such as melting temperature, mold temperature, injection temperature, and pressure also help to control shrinkage during production.
