Water resistance refers to the ability of the material to resist water damageSoftening coefficientIt indicates the water resistance of materials. The mechanical properties of materials with strong water resistance are not easy to reduce.
Chinese name
Water resistance
Foreign name
water resistance
Definition
Material resistance to water damage
Represent
Softening coefficient
Test
Water resistance test, water resistance accelerated test
Water resistance refers to the ability of materials to resist water damage.The damage of water to material performance is reflected in different aspects, the most obvious performance is the reduction of mechanical properties of materials.Water resistance is usually expressed by softening coefficient, which is calculated as follows:
Where, Kf——Softening coefficient of materials;fone——Compressive strength of material under water absorption saturation state, MPa; fzero——Compressive strength of materials in dry state, MPa.
After the material absorbs water, the bonding force between its internal particles is weakened, which leads to the decrease of material strength in varying degrees.The larger the softening coefficient is, the stronger the material's resistance to water damage is, that is, the stronger the water resistance is.The softening coefficient is between 0 and 1.
Softening coefficient is an important basis for selecting water resistant materials.For materials directly used in water or seriously damped, the softening coefficient should not be less than 0.85;The softening coefficient of lightly damped materials should not be less than 0.75.It is generally considered that materials with softening coefficient greater than 0.85 are water resistant materials.[1]
Water Resistance Test
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Test principle: measure the changes of appearance, physical or mechanical properties of soaked parts after the specified test soaking cycle under the condition of water medium.
Immersed parts: 1) Immersed parts include samples, test samples and real objects.2) The sample size shall be determined according to the measured performance and relevant standards.The size and number of test panels cut from the real object shall be determined according to the measured performance and the provisions of relevant standards.3) In order to determine the initial performance, the sample plate with the same process as the real object shall be prepared in advance.4) Immersed parts shall be randomly sampled and grouped with the same batch.There are generally no less than 5 samples in each group.
Test conditions:
(1) The immersion condition medium of the sample is distilled water, and the water temperature is 23 ℃± 2 ℃ or 40 ℃± 2 ℃.The water temperature for arbitration test shall be 23 ℃ ± 2 ℃.Other different test water temperatures may also be used with the consent of the parties concerned.
The water resistance test period is 30 days. For materials with good water resistance, the test period can be extended appropriately.
When determining the wet ultimate bending strength, the test cycle is 14 days.Take a group of samples for testing every week untilbending strength It ends when the rate of change over time approaches zero.If necessary, use other test cycles.
(2) Immersion conditions of the test sample The test sample is fixed and then put into the river, river, lake or sea without serious pollution, or put into the actual water area for immersion.The sample plate shall not contact the sludge at the bottom of the water, but shall be deep enough to avoid exposing the water surface due to the change of the water level of the network.
There are two methods for fixing the sample plate, either of which can be selected.
1) The test sample plate is fixed on the floating boat with a frame.Frame material can be made of glass fiber reinforced materialGlass fiber reinforced plasticsWood or steel coated with waterproof paint.
2) The frame shall be made of steel and the surface shall be coated with waterproof paint.Fix the two ends of the sample (not exceeding the sampling position) on the frame. The sample plates do not contact each other, and then lift the frame into the water with wire rope.The test period of sample soaked in water is generally not less than 5 years, and samples can be taken according to the following periods (years): 0.5, 1, 2, 3, 5, 7, 10, etc.
(3) Soaking test shall be carried out according to the actual use conditions of the real object.When the sample is taken back from the place where the object is located (river, lake or sea), it shall be placed in the water immersion state of the object.
Test procedure
(1) Test initial performance: according to the tested performance, test according to the relevant standards.
(2) Place immersion pieces: ① Soak the samples that have been cleaned of surface dust and oil stains in water, and the samples shall not contact each other, or between the samples and the container wall; ②Soak the test sample according to the soaking conditions, clean the test sample every 3-6 months, maintain the frame, observe the appearance change of the test sample and whether the number falls off, and if it falls off, make up in time; ③Soak the object according to the soaking conditions.
(3) After the sampling test reaches the specified test immersion period, take out the sample, without state adjustment, and complete the test within 30 minutes according to the measured performance according to the relevant standards.
The sample plate shall be processed and tested immediately after being taken out, or it shall be placed in a container soaked in water first, taken out during processing, and tested immediately after processing.The test sample shall not be taken out for more than 3 days until the test is completed.
The material object shall be processed and tested immediately after being taken out, and the longest time shall not exceed 3 days.When the surface of the object is immersed in water on one side, measurebending strength The immersion surface shall be under pressure or determined according to the use of the product.[2]
Accelerated water resistance test
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Test principle: measure the change of appearance, physical or mechanical properties of the sample after the specified test immersion period under the water medium condition of the specified temperature.
2) The sample size shall be determined according to the measured performance and relevant standards.
3) The samples shall be randomly sampled and grouped with the same batch.In addition to a group of samples for determining the initial performance, the number of sample groups shall be determined according to the number of test cycles and test requirements, and each group of samples shall not be less than 5.
4) The sample number shall be clear and durable, and shall not affect the test results.
Test conditions:
1) The medium is distilled water orDeionized water。During arbitration test, the resistivity of water shall not be less than 500 Ω· m.
2) Soak in 80 ℃± 2 ℃ water.Materials with good temperature resistance can be soaked in water at 95 ℃± 2 ℃;Materials with poor temperature resistance can be soaked in 60 ℃± 2 ℃ water.
3) Unless otherwise specified, boiling in distilled water for 2h shall be adopted for screening test.
4) Soak the sample for 24h as a cycle.The sample shall be put in when the water temperature reaches the specified value, and the timing shall be started.
5) Unless otherwise specified, it can generally be selected from the following cycles: ① epoxy resin based or phenolic resin basedGlass fiber reinforced plasticsNumber of cycles: 1, 2, 6; ②polyester resinThe number of cycles of glass fiber reinforced plastics is 1/3, 1/2, 1, 2, 3, 6.
Test steps:
(1) The initial performance of the test shall be tested according to the measured performance and relevant standards.
(2) Place the sample. The sample whose surface has been cleaned of dust and oil stain shall be immersed in a water bath device at the specified temperature. The samples shall not contact each other, the container wall and the heating pipe.
(3) After the sampling test reaches the specified test immersion period, take out the sample to check its appearance, and test the performance according to one of the following two methods.
1) After the sample is conditioned as required, it shall be tested according to the measured performance and the relevant standards.
2) The sample does not need state adjustment. Take it out of the water bath and put it into room temperature distilled water or deionized water for cooling. The water immersion time shall not be less than 15min. The sample taken out of the water bath shall be tested within 30min.[2]
