Ethan Clarke
Testing the durability of plastic is a critical step in the product development process. It helps manufacturers ensure that their products meet the necessary requirements and specifications, and it gives them confidence in their creations. There are a variety of tests that can be carried out to determine durability, including vibration testing, tensile testing, and temperature testing. Accelerated ageing tests are also used to measure the evolution of materials against extreme atmospheric conditions and to calculate shelf life. These tests are essential to ensure products comply with quality requirements and legislation.
| Characteristics | Values |
|---|---|
| Accelerated Ageing Testing | Measure the evolution of materials against extreme atmospheric contexts |
| Temperature Testing | 1800 degrees Fahrenheit |
| Tensile Testing | Measures the strain of the product as pressure is increased |
| Vibration Testing | Conducted on the production floor or within a laboratory setting |
| Weathering Testing | Predict how plastic products will withstand over time |
| Brittleness Temperature | Judge the relative merits of various materials for low-temperature flexing or impact |
| Compressive Strength | Calculated as the psi required to rupture or deform the specimen |
| Deflection Temperature | Temperature at which deflection occurs under established loads |
| Deformation Under Load | Indicates the ability of rigid plastics to withstand continuous short-term compression without yielding |
| Flammability | Specimen is classed as burning, non-burning, or self-extinguishing |
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What You'll Learn
- Accelerated ageing testing: exposing plastic to extreme temperatures to speed up the ageing process
- Weathering testing: determining plastic's resistance to outdoor weather conditions
- Compressive strength testing: measuring the psi required to rupture or deform plastic
- Deflection temperature testing: finding the temperature at which plastic deflects under load
- Flammability testing: testing plastic specimens to determine their resistance to burning
Accelerated ageing testing: exposing plastic to extreme temperatures to speed up the ageing process
Accelerated ageing tests are used to measure how materials withstand extreme atmospheric conditions and predict how plastic products will fare over time. The tests expose the materials to specific climate conditions that usually stimulate the extreme conditions they will suffer during their shelf life.
Extreme temperatures act as an accelerator of the ageing process in materials and products. High temperatures may cause the degradation of plastics, corrosion in metals, or even loss of adhesion in paints and coatings. Low temperatures normally affect polymers due to their fragilizing effect.
During accelerated ageing tests, samples are exposed to repeated cycles of extreme heat and cold, mimicking daily or seasonal temperature fluctuations. This method is often used in the automotive industry to test components like engines and braking systems, simulating real-world conditions such as hot desert climates during the day and freezing temperatures at night.
Thermal shock testing is a type of accelerated ageing test that involves rapid exposure of materials to extreme temperature differences over a short period. This method helps evaluate a product's resistance to cracking, warping, or other forms of failure caused by sudden thermal gradients. Thermal shock chambers are specialized devices with distinct temperature settings—high, low, and sometimes ambient—to facilitate rapid temperature transitions and simulate extreme environments.
Temperature testing is typically conducted in laboratories using a testing machine or furnace to expose the product to elevated temperatures. The product is placed in a testing frame where pressure is applied, and the strain on the product is measured as the pressure increases. The data from these tests help determine the durability and lifespan of the product.
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Weathering testing: determining plastic's resistance to outdoor weather conditions
Weathering testing and ageing testing are used to determine how well plastic products will withstand the test of time. Accelerated ageing tests are used to measure how materials evolve in extreme atmospheric contexts, and specific climate conditions are used to simulate the extreme conditions that materials will face during their shelf life. High temperatures, for example, may cause the degradation of plastic, while low temperatures can affect polymers, making them more fragile. Sudden temperature changes can also cause mechanical problems or cracks.
Temperature testing is typically carried out in laboratories, where a testing machine will measure how materials behave when exposed to extreme temperatures. This can be done by placing the product in a furnace with temperatures of up to 1800 degrees Fahrenheit.
Vibration testing is another method that can be used to test the durability of plastics. This can be conducted on the production floor or in a laboratory, and it involves using a vibration table or a servo-hydraulic shaker to provide shock vibrations to the product.
When it comes to plastics intended for outdoor use, weathering testing is particularly important. Outdoor materials are exposed to weather conditions that can cause them to develop cracks and fade in colour. Plastic, in particular, tends to stretch at elevating temperatures, and poor-quality plastic can generate cracks that disturb the coated layer and affect the overall appearance. Long exposure to UV light from sunlight can also cause the colour of plastic to fade.
To test the weathering resistance of plastics, manufacturers use a UV Weathering Chamber to generate similar weathering conditions, including rain, UV rays, direct sunlight, moisture, and relative humidity. This allows manufacturers to observe how the plastic resists cracking and weakening and how the coating they apply behaves under these conditions.
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Compressive strength testing: measuring the psi required to rupture or deform plastic
Compression testing is a fundamental mechanical testing method used to determine a material's behaviour under applied crushing loads. This type of testing is often performed on finished products to evaluate their compressive strength. It is also used to test the strength of materials with a "sandwich" construction, such as the body panels of the DeLorean DMC-12, which consist of two outer fibrous glass layers that sandwich resin-impregnated inner foam.
Compressive strength testing for plastic specifically involves applying pressure to a test specimen with a specific geometry using platens or specialised fixtures on a universal testing machine. The specimen's deformation is then measured by a strain gauge or a compressometer, which records the change in distance between two fixed points on the specimen caused by the exerted load.
ASTM standards for compressive testing specify that for isotropic materials, at least five specimens should be tested, while for anisotropic materials, at least ten specimens are required, with five tested normally and five tested in parallel with the principal axis of anisotropy.
The data collected from compressive strength testing helps resin makers, design engineers, and manufacturers ensure their processes are stable and consistent and that the right material is used for the right application. It is also used by quality assurance departments to ensure that finished products meet the required specifications for compressive properties.
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Deflection temperature testing: finding the temperature at which plastic deflects under load
Heat deflection temperature (HDT) is a critical test for determining the durability of plastic products. It is the temperature at which a plastic sample deforms under a specified load and high heat. The HDT test measures the plastic's ability to remain stiff or rigid under these conditions. The standard measuring system for HDT is the American Society for Testing and Materials (ASTM) D 648, comparable to the ISO 75 international standard.
To perform the test, a specimen is loaded in three-point bending in the edgewise direction. The test specimen, a bar measuring 127 x 13 x 12 mm, is subjected to a centered standard flexural stress of either 0.455 MPa or 0.46 MPa (67 psi) for soft plastics. The temperature is then increased at 2 °C/min until the specimen deflects by 0.25 mm, which is considered an arbitrary deflection value with no particular physical significance.
HDT is crucial in the engineering, design, and manufacturing of plastic products. It helps determine the suitability of a plastic for a specific application, particularly if it needs to maintain its shape and size under pressure and high temperatures. For example, a plastic with a higher HDT will be more suitable for applications exposed to higher temperatures, as it will remain rigid for a more extended period.
Additionally, HDT is essential in processes like injection moulding. An injection-moulded plastic part is considered "safe" to remove from its mould once it is near or below the HDT, as this ensures that part deformation will be within acceptable limits.
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Flammability testing: testing plastic specimens to determine their resistance to burning
Plastic is a versatile material used in a wide range of applications, from consumer electronics to textiles. When it comes to determining the durability of plastic, one critical aspect is its flammability or resistance to burning. Flammability testing helps assess the safety and performance of plastic materials when exposed to ignition sources. Here is an overview of flammability testing for plastic specimens:
Test Procedures:
Flammability testing of plastics involves a series of controlled experiments to evaluate the burning behaviour of the material. Specimens are typically moulded from the plastic material being tested and oriented horizontally or vertically, depending on the specific test method. A flame ignition source, such as a Bunsen burner, is then applied to the specimen for a specified duration. The time taken for the flame to extinguish itself, the distance the burn propagates, and the linear burning rate are measured.
Flame Ratings:
Plastic materials are assigned flame ratings based on their performance during flammability tests. The ratings indicate the material's ability to self-extinguish and its behaviour regarding dripping flaming particles. Common flame ratings include V0, V1, and V2 for vertical ratings and HB for horizontal burning. The 5VA and 5VB ratings are for materials subjected to more severe flame ignition sources.
Test Standards:
Several standards have been established to ensure consistent and reliable flammability testing of plastics. UL 94, harmonized with IEC and ISO standards, provides specifications for testing the flammability of plastic materials used in devices and appliances. UL 746A and IEC standards outline test procedures for assessing the ignition resistance of plastics to electrical ignition sources. These standards help classify materials based on their burning characteristics.
Applications:
Flammability testing is crucial for plastics used in various industries, including consumer electronics, textiles, transportation, and construction. In some cases, flammability standards are mandated by legislation and regulations to ensure public safety. For example, flammability testing of textiles became standardised in the UK during the late 1950s, following numerous fire-related fatalities.
Limitations and Considerations:
While flammability testing provides valuable insights into the burning behaviour of plastics, it has limitations. These tests focus on controlled laboratory conditions and may not fully represent real-world scenarios. Additionally, the ageing of plastics over time due to exposure to extreme temperatures, atmospheric conditions, and sudden temperature changes can affect their flammability characteristics. Therefore, accelerated ageing tests are conducted to predict how plastic products will withstand over time and comply with quality and safety requirements.
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Frequently asked questions
Accelerated ageing testing is used to measure how materials react to extreme atmospheric conditions, such as extreme temperatures, to predict their lifespan.
Vibration testing is conducted to determine the durability of a product by exposing it to shock vibrations using an electrodynamic vibration table or a servo-hydraulic shaker.
Deflection temperature is the temperature at which an arbitrary amount of deflection occurs in a plastic specimen under established loads.
The compressive strength of plastic is determined by mounting a specimen in a compression tool between testing machine heads that exert a constant rate of movement until the specimen ruptures or deforms.
Deformation under load indicates the ability of rigid plastics to withstand continuous short-term compression without yielding or loosening when fastened with bolts, rivets, etc.
