The issue of low-temperature impact strength

Generally speaking, after adjustment to standard conditions, it can be placed in a low-temperature environment for more than 1 hour.

In a low-temperature environment for 4 hours, it is generally required that the impact test be completed within 10 seconds of leaving that low-temperature environment.

Thank you for letting me know. However, the duration required in low-temperature environments seems to vary according to different sources – some say half an hour, while others say several hours. What determines this?

This post was last edited by QXZ-1966 on 2009-7-31 08:55. The standard is 4 hours, as specified by both the automotive industry standards and the building materials industry standards. Half an hour is not enough to bring the entire experimental material to a low temperature. The requirement is that the entire experimental material be in the low-temperature state you specified; for the high and low temperature cycling experiment, the low-temperature state is required for 3 hours.

Are there different standards for different materials?

It seems that the time requirements are the same, with only a difference in the low-temperature environment temperature.

This post was last edited by leonqin on 2009-7-31 14:10. I have a different opinion on this. Regarding LZ’s question, as for the Charpy and Izod impact tests on plastics at low temperatures, the holding time at such low temperatures is not specified in either ISO 179-1 (Charpy) or ISO 180 (Izod). The standard ISO 291, which governs the condition of plastic test specimens, also does not specify any holding time for specimens used in low-temperature tests. It only specifies that in the standard environments of 23°C/50% R.H. and 27°C/65% R.H., the duration must be at least 88 hours; and in a room temperature range of 18–28°C, the duration must be at least 4 hours. ASTM D618, the standard for conditioning plastic specimens referenced by ASTM D6110 (Charpy) and ASTM D256 (Izod), provides many more options for specimen conditioning. However, regarding the holding time during low-temperature tests, it only specifies an upper limit (not more than 5 hours), while stating that equilibrium is sufficient as the lower limit. Therefore, although many plastic datasheets provide Charpy and Izod values at -30°C and cite the aforementioned standards, there is no clear standard regarding this holding time; different organizations and studies employ different procedures. For example, a related article titled \"Low Temperature Impact Strength of Cellulosic Plastics\" describes that the conditioning procedures and low-temperature testing procedures specified by ASTM were not fully standardized. In these tests, the test specimens were first conditioned at 70 degrees F and 50% relative humidity for 24 hours before being subjected to low-temperature conditioning at -20 degrees F. The specimens were then held at that low temperature for at least 2 hours, after which they were placed in a Charpy testing machine set at 70 degrees F, and testing was carried out within 15 seconds. According to GB/T 9979 \"Test Methods for Mechanical Properties of Fiber-Reinforced Plastics at High and Low Temperatures\", this standard applies to mechanical property tests of unidirectionally fiber-reinforced plastics at high and low temperatures ranging from -150°C to 200°C; it can also be used as a reference for testing the mechanical properties of resins and other types of reinforced plastics, even outside this temperature range. Additionally, for the 5.5 installation specimens, at the test temperature, the holding time is as follows: 15 minutes for carbon fiber reinforced plastics ； Glass fiber reinforced plastic is 20 min. Refer to GB/T 2423.22 Environmental testing of electrical and electronic products – Part 2: Test methods – Test N: Temperature cycling (equivalent to IEC 60068-2-14). This standard specifies the holding time of the sample at high and low temperatures during the temperature cycling test. Among them, for 1.6.2, the length of each exposure test time t1 at both low and high temperatures depends on the heat capacity of the test sample. According to relevant specifications, the exposure time should be 3 hours, 2 hours, 1 hour, 30 minutes, or 10 minutes. It can be seen that here, by taking into account both the sample size and thermal equilibrium, a standard time is provided. Given that electronic products are generally composed of various materials such as plastic and metal, their heat diffusion efficiency is not as high as that of pure plastic; therefore, pure plastic reaches temperature equilibrium in less time. The standard specimens for Charpy and Izod impact tests are actually quite small, so keeping them at that temperature for 1 hour is sufficient overall. I’m not sure what specific standards the moderator is referring to in the automotive and construction materials industries As far as I know, in the test standards for various specific materials in the automotive industry, impact tests often refer to the aforementioned ISO/ASTM standards. In the test standards for automotive electronic products established by vehicle manufacturers, such as GMW3172 General Specification Electrical/Electronic, the holding times at high and low temperatures during temperature cycling are specified as 20 minutes, 40 minutes, 60 minutes, or 90 minutes, depending on the size and properties of the DUT. This means that the time required to reach thermal equilibrium will not be as long as 4 hours; generally, 30 minutes to 1 hour is sufficient, and it is reasonable to set it at 1 hour as a precaution.

Reply to Leonqin on floor 8: The data you provided refer to spline impacts, whereas many products have requirements regarding resistance to low-temperature impacts; such requirements fall outside the standards you listed and are instead part of the product standards. Check the low-temperature test for plastic-steel doors and windows: it requires maintaining a temperature of -10°C for 4 hours, with the impact test to be carried out within 10 minutes after leaving that temperature ； Check QC/T15, the general test methods for automotive plastic products; it specifies that the low-temperature exposure time must be no less than 4 hours.

The last edit to this post was made by leonqin on 2009-7-31 at 17:00. In LZ’s question regarding \"the impact strength of low-temperature materials,\" my understanding is that it refers to the notched/uncnotched impact strength of the materials using the Charpy/Izod tests; therefore, standard specimens must be prepared, following the relevant ISO/ASTM standards I mentioned earlier. I couldn’t find the low-temperature testing standards for plastic-steel doors and windows mentioned by the moderator. I took a look at QC/T 15; this standard deals with testing methods for finished products, and its impact resistance test is not the same as the material impact strength test mentioned earlier. Moreover, I think the moderator probably misinterpreted this standard, as there are two places in it that mention the requirement of “not less than 4 hours”. First, under ‘4.3 Sample Pretreatment’: Samples shall be randomly selected from products that have been stored for at least 24 hours since manufacturing. Before testing, the samples must be placed in the environment specified in 4.1 for no less than 4 hours, and then the testing can proceed. ”The “environment specified in 4.1” here refers to “Standard environment in 4.1: The standard environment for testing shall comply with the relevant provisions of GB 2918”. GB 2918 is the national standard equivalent to the ISO 291 standard I mentioned earlier, which deals with the conditioning of plastic test specimens. The standard conditions specified here are two: 23°C/50% R.H. for a period of not less than 88 hours, and 27°C/65% R.H. for the same duration; in addition, the specimens must be kept at a room temperature of 18–28°C for at least 4 hours. There is no low-temperature holding time. Secondly, under ‘5.1.4.3 Cold resistance test’: Adjust the temperature of the low-temperature chamber to the value specified in Table 4. Once the desired temperature is reached, place the sample in the chamber for at least 4 hours, then remove it and conduct inspections according to the items specified in Article 6. ”This is a dedicated cold resistance test. The low-temperature holding time in such a test must not be construed as the time during which the sample is kept at low temperature prior to undergoing other performance tests; moreover, the low-temperature holding time in a cold resistance test is usually much longer than the time it takes for the sample to reach thermal equilibrium. The impact resistance test in this standard also does not specify the holding time under low-temperature conditions. Tables 4 and 15 cited therein only provide some recommended temperatures, including -30°C and -40°C, without any information on insulation time. Incidentally, manufacturers’ standards are usually higher than industry standards; the GMW3172 standard mentioned by me earlier by General Motors is considered one of the most stringent standards around. This standard is a test standard for products, not a test standard for standard specimens of materials. The reason I cite this standard is that the ISO/ASTM test standards for reference specimens of materials do not specify a holding time under low-temperature conditions. The IEC 60068-2 series standards cited in GMW3172 are commonly used environmental testing standards in the electronics/automotive industries; IEC 60068-2-14 specifies the holding time of specimens at high and low temperatures during temperature variation tests. By holding time, I mean a period longer than the time it takes for the specimen to reach thermal equilibrium, as in temperature cycling tests, the specimen is required to remain at that temperature for a certain period after its core temperature reaches the ambient temperature.

I hope the LZ can describe in detail which specific test needs to be carried out.