High-Strength Plastics – 4 Ways To Measure Strength
One of best test methods which are used to verify the quality of the plastics is Tensile Test. The Tensile Test is usually performed in the plastic industries to measure the tensile strength of the plastic materials. This test can be carried out with the help of a tensile testing machine. Using the tensile testing machine, the manufacturer can accurately determine the strength of the material that how much tensile force a . Measuring High-Strength Plastics. Flexural strength. How well does the material resist deformation under load? This number indicates the load required to cause a given test sample to show a 5% deformation/strain of its outer surface. Some of the best plastics for flexural strength .
When evaluating a material for use in a particular application, engineers usually look first at the material properties data sheet or material data sheet for short. These are available on-line for most plastic materials. This sheet will give typical values for a variety of properties. Usually it will include values for physical properties and mechanical properties as well as thermal and how to build a toolshed properties.
Typically, the material properties data sheet will include what ASTMISO or UL test was used at to arrive at the value and the units srrength value is given in as well as the data. Here we will take a closer look at some of the mechanical properties used to evaluate material strength. Let me know in the comments section below.
Looking for more information on material properties? Download our free Plastic Manufacturing Glossary. Your email address will not be published. The term refers to the maximum stress a particular plastic can withstand while hpw pulled or stretched without breaking. The highest point of the stress strain curve is the UTS. Other materials, such as most metals, will experience some plastic deformation before fracture. The values are most important in brittle materials as there is no yield point.
Tensile Stress at Break or Ultimate Tensile Stress refers to the elongation of a material that is plasitc to tension until it breaks. It is commonly expressed in MPa or psi.
Flexural Modulus, sometimes referred to as the bending modulus, is the tendency of a material to bend. It is the ratio stress to strain in a flexural deformation and is expressed in units of force per area. It was named after the 19 th century British scientist Thomas Young. It is often referred to as the Modulus of Elasticity. It is a ratio of the stress along an axis to the strain along sttrength axis.
Shear Strength is the force per unit area at failure divided by tsst density. Shear forces are unaligned forces pushing one part of an object in one direction but another part of that body in another direction. Rockwell Hardness refers to a method of testing the hardness of materials. In this case hardness is defined as the resistance of a polymer to penetration. The Rockwell scales are the most widely how to upload a photo on twitter tests for hardness.
The ASTM test determines the energy per unit thickness required to break a test specimen under flexural impact. The test specimen is held as a vertical cantilevered beam and is impacted by a swinging pendulum. The energy lost by the pendulum is equal to plastc energy absorbed by the test specimen.
Elongation at Break is the ratio hw the initial length and tthe changed length after breakage of the test specimen. Leave a Reply Cancel reply Plashic email address will not be published.
Flexural Strength Testing of Plastics
Apr 11, · Why and how to test the tensile strength of plastic?Importers and manufacturers of plastic products need to understand the results of this common mechanical. When the indenter is pressed into the plastic specimen so that the base rests on the plastic surface, the amount of indentation registers on the dial indicator. This test measures the indentation into the plastic of the indenter under load, according to a scale of 0 to There is no unit of measurement. Jul 04, · Change the plastic properties and the resulting product might have serious issues or the mold can simply no longer be used! A simple way of identifying what type of plastic was used is outlined in this article. Quite useful. It is also important to confirm the properties of the plastic used. We made some videos on the way to test plastic.
Artificial Weathering has been defined by ASTM as "The exposure of plastics to cyclic laboratory conditions involving changes in temperature, relative humidity and ultraviolet UV radiant energy, with or without direct water spray, in an attempt to produce changes in the material similar to those observed after long-term continuous outdoor exposure. Because weather varies from day to day, year to year, and place to place, no precise correlation exists between artificial laboratory weathering and natural outdoor weathering.
However, standard laboratory test conditions produce results with acceptable reproducibility and which are in general agreement with data obtained from outdoor exposures. Fairly rapid indications of weatherability are therefore obtainable on samples of known plastics which through testing experience over a period of time, have general correlations established.
There is no artificial substitute for predicting outdoor weatherability on plastics with no previous outdoor history. ASTM E Brittleness Temperature is of some use in judging the relative merits of various materials for low temperature flexing or impact.
However, it is specifically relevant only for materials and conditions specified in the test and the values cannot be applied directly to other shapes and conditions.
The brittleness temperature does not put any lower limit on service temperature for end-use products. Brittleness temperature is sometimes used in specifications. Conditioned specimens are cantilevered from the sample holder in the test apparatus which has been brought to a low temperature that at which specimens would be expected to fail.
When the specimens have been in the test medium for 3 minutes, a single impact is administered and the samples are examined for failure. Failures are total breaks, partial breaks, or any visible cracks. The test is conducted at a range of temperatures producing varying percentages of breaks. ASTM D Compressive properties are obtained by mounting in a compression tool between testing machine heads which exert constant rate of movement. The compressive strength of a material is calculated as the psi required to rupture the specimen or deform the specimen a given percent age of its height.
It can be expressed as psi either at rupture or at a given percentage of deformation. The compressive strength of plastics is of limited design value, since plastic products except foams seldom fail from compressive loading alone. The compressive strength figures, however, may be useful in specifications for distinguishing between different grades of a material, and also for assessing, along with other property data, the over-all strength of different kinds of materials.
Deflection Temperature shows the temperature at which an arbitrary amount of deflection occurs under established loads. It is not intended to be a direct guide to high temperature limits for specific applications. It may be useful in comparing the relative behavior of various materials in these test conditions, but it is primarily useful for control and development purposes. A specimen is placed on supports 4 inches apart and a load of 66 or psi is placed on the center.
The temperature at which the bar has deflected 0. Deformation Under Load indicates the ability of rigid plastics to withstand continuous short-term compression without yielding and loosening when fastened as in insulators or other assemblies by bolts, rivets, etc. It does not indicate the creep resistance of a particular plastic for long periods of time. It is also a measure of rigidity at service temperatures and can be used as identification for procurement.
The specimen is placed between the anvils of the testing machine, and loaded at psi. Sometimes other loadings may be specified. The gauge is read 10 seconds after loading, and again 24 hours later. The deflection is recorded in mils. The original height is calculated after the specimen is removed from the testing machine by adding the change in height to the height after testing.
By dividing the change in height by the original height and multiplying by , the percent deformation is calculated. This test may be run at Durometer Hardness instrument has a pointed indenter projecting below the base face of the pressure foot. When the indenter is pressed into the plastic specimen so that the base rests on the plastic surface, the amount of indentation registers on the dial indicator.
This test measures the indentation into the plastic of the indenter under load, according to a scale of 0 to There is no unit of measurement. Readings taken immediately after application may vary from those taken after pressure has been held for a time, because of creep. This test is preferred for polyethylene, because the Rockwell test loses meaning when excessive creep is encountered.
For other materials acetate, acetal, etc. Flammability for plastics thicker than 0. If the specimen continues to burn, it is timed until it stops or a 4 in. A specimen which burns to the 4 in. If the specimen does not continue burning to the 4 in. A Bunsen burner, placed so the flame contacts the end of the specimen, is held 30 seconds and then removed. If the specimen does not ignite, the burner is returned for another second attempt.
The burning is measured along the lower edge of the specimen. Flexural properties of plastics are obtained by placing a specimen on two supports spaced 4 in. A load is applied in the center at a specified rate and the loading at failure psi is the flexural strength. In bending, a beam is subject to both tensile and compressive stresses.
Because most thermoplastics do not break in this test even after being greatly deflected, the flexural strength cannot be calculated. Haze and Luminous Transmittance of transparent plastics. In this test, haze of a specimen is defined as the percentage of transmitted light which, in passing through the specimen, deviates more than 2.
Luminous transmittance is defined as the ratio of transmitted to incident light. These qualities are considered in most applications for transparent plastics. They form a basis for directly comparing the transparency of various grades and types of plastics.
Izod Impact testing is done by clamping a specimen in the base of a pendulum testing machine so that it is cantilevered upward with the notch facing the direction of impact. The pendulum is released, and the force consumed in breaking the sample is calculated from the height the pendulum reaches on the follow-through.
The Izod impact test indicates the energy required to break notched specimens under standard conditions. It is calculated as ft. The Izod value is useful in comparing various types of grades of a plastic. In comparing one plastic with another, however, the Izod impact test should not be considered a reliable indicator of overall toughness or impact strength. Some materials are notch-sensitive and derive greater concentrations of stress from the notching operation.
The Izod impact test may indicate the need for avoiding sharp corners in parts made of such materials. For example, nylon and acetal-type plastics, which in molded parts are among the toughest materials, are notch sensitive and register relatively low values on the Izod impact test.
Luminous Reflectance, transmittance and color. This test is the primary method to obtain colorimetric data. Properties determined include: 1 total luminous reflectance or luminous directional reflectance; 2 luminous transmittance; and 3 chromaticity coordinates x and y color. A specimen is mounted in a special device and along with it a comparison surface white chalk. The specimens are placed in the device and light of different wave-length intervals is impinged against the surface.
Reflected or transmitted light is then measured to obtain property values. Permanent Effect of Heat is of particular value in connection with established or potential applications which involve service at elevated temperatures. It permits comparison of various plastics and grades on one plastic in the form of test specimens, as well as molded parts in finished form. Rockwell hardness can differentaite relative hardness of different types of a given plastic.
But since elastic recovery is not involved as well as hardness, it is not valid to compare hardness of various kinds of plastic entirely on the basis of this test. Rockwell hardness is not an index of wear qualities or abrasion resistance. For example, polystyrenes have high Rockwell hardness values but poor scratch reistance. A steel ball under a minor load is applied to the surface of the specimen. This indents slighly and assures good contact.
The gauge is then set to zero. The major load is applied for 15 seconds and removed, leaving the minor load still applied. The indentation remaining after 15 seconds is read directly off the dial. The size of the balls and the loadings vary, and values obtained with one set cannot be correlated with values from another set. Shear Strength data is obtained by mounting a specimen in a punch type shear fixture and the punch 1 in.
D is pushed down at a rate of 0. Shear strength is particularly important in film and sheet products where failures from this type load may often occur. For the design of molded and extruded products it would seldom be a factor. Plastic sheets or molded plastic discs measuring 0. Specific Gravity is a strong element in the price factor and thus has great importance. Polyethylenes, for example, may have density variation, depending upon the degree of "packing" during molding, or the rate of quench during extrusion.
Although specific gravity and density are frequently used interchangeably, there is a very slight difference in their meaning. Specific gravity is the ratio of the weight of a given volume of material at The deflection scale is set at zero. The motor is engaged and the loading increased, with deflection and loading figures recorded at intervals. A curve is drawn of deflection versus load, and from this is calculated stiffness in flexure in pounds per square inch.
This test does not distinguish the plastic and elastic elements involved in the measurement and therefore a true elastic modulus is not calculable. Instead, an apparent value is obtained and called "stiffness in flexure.