This standard specifies the method of applying a three-point bending load to the specimen to determine the bending strength, constant deflection bending stress, bending elastic modulus and draw a load-deflection curve. This standard is applicable to castings of resins for fiber reinforced plastics and special casting resins. GB/T 2570-1995 Test method for bending properties of resin castings GB/T2570-1995 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Test method for flexural properties of resin casting body
Subject content and scope of application
GB/T2570-1995
Replaces GB2570-81
This standard specifies the method of applying a three-point bending load to a specimen to determine the bending strength, constant deflection bending stress, bending elastic modulus and draw a load-deflection curve.
This standard applies to castings of resins for fiber-reinforced plastics and special casting resins. 2 Test specimens
2.1 The shape of the bending specimen is shown in Figure 1.
Figure 1 Bending specimen
2.2 Specimen size: The thickness h of the arbitration specimen is 4±0.2mm, and the thickness h of the general specimen is 3~6mm (the thickness tolerance of a group of specimens is ±0.2mm). The width b is 15mm. The length L is not less than 20h. 2.3 The number of specimens shall be in accordance with Chapter 3 of GB/T2567-1995. 3 Test conditions
3.1 Test environment conditions shall be in accordance with Chapter 4 of GB/T2567-1995. 3.2 Test equipment shall be in accordance with Chapter 7 of GB/T2567-1995. 3.3 The schematic diagram of the 3-point bending test device is shown in Figure 2, the span L is (16±1)h, the radius R of the loading upper pressure head is 5±0.1mm, and the radius r of the specimen support circle is 2±0.2mm.
Approved by the State Administration of Technical Supervision on December 20, 1995, 748
Implemented on August 1, 1996bzxz.net
GB/T2570—1995
Figure 2 Schematic diagram of the 3-point bending test device
1~ Sample support, 2-Loading upper pressure head, 3-Sample 3.4 Conventional test speed 2~10mm/min, when measuring the bending elastic modulus, the test speed is 2mm/min; arbitration test speed is 2 mm/min.
4 Test steps
4.1 Sample preparation is in accordance with Chapter 2 of GB/T2567—1995. 4.2 Sample appearance inspection is in accordance with Chapter 3 of GB/T25671995. 4.3 Sample state adjustment is in accordance with Chapter 5 of GB/T2567-1995. 4.4 Number the qualified samples, measure the width and thickness of the three points near the mid-span (center of the span) of the sample, and take the arithmetic mean. The measurement accuracy shall comply with Chapter 6 of GB/T 2567-1995.
4.5 Adjust the span L and the position of the upper pressure head to an accuracy of 0.5mm. The upper pressure head is located in the middle of the support and parallel to the support. 4.6 Place the sample in the middle of the support. The length direction of the sample is perpendicular to the support and the upper pressure head. 4.7 Adjust the loading speed, select the load range of the testing machine and the range of the deformation instrument. 4.8 When measuring the bending strength or bending stress, load uniformly and continuously at the specified speed until failure, and record the failure load value or the maximum load value. For materials that do not show failure at a deflection equal to 1.5 times the thickness of the sample, record the load at the deflection. 4.9 When measuring the elastic modulus or drawing the load-deflection curve, install the deflection measuring device at the bottom of the mid-span of the sample or between the upper pressure head and the lead-out device of the support. Apply initial load (about 5% of the failure load), check and adjust the instrument, start the testing machine and apply load at the specified speed. Within 40% of the failure load, record the load and corresponding deflection value at a certain interval. If there is an automatic recording device, continuous loading can be performed. 4.10 The specimens that fail outside the middle one-third of the span (L) should be discarded and another specimen should be taken to supplement. If there are less than 5 valid specimens in the same batch, the test should be repeated.
5 Calculation
5.1 Flexural strength or flexural stress is calculated according to formula (1): df=
Where: α-
Flexural strength or flexural stress, MPa;
26·h2
P-Failure load or maximum load or load at a certain deflection (deflection equal to 1.5 times the thickness of the specimen), N; L-span, mm;
b-specimen width, mm;
h-----specimen thickness, mm.
（1）
GB/T 2570--1995
If f/L>10%, taking into account the influence of the bending moment caused by the horizontal component of the support under the deflection, the bending strength at can be calculated according to the following formula
Where: 」
Mid-span deflection when the specimen fails, mm.
The rest is the same as formula (1).
5.2 Flexural modulus is calculated according to formula (2)
Flexural modulus, MPa;
Where: E,
[1 ~- 4(f/L)]
26·h2
L'·AP
-corresponds to the load increment value of the initial straight line segment on the load-deflection curve, N; Af---mid-span deflection corresponding to the load increment △P, mm. The rest is the same as formula (1).
5.3 Test results shall be in accordance with Chapter 8 of GB/T2567-1995. 5.4 Test report shall be in accordance with Chapter 9 of GB/T2567-1995. Additional remarks:
This standard was proposed by the State Bureau of Building Materials Industry and is under the jurisdiction of the National Technical Committee for Standardization of Fiber Reinforced Plastics. This standard was drafted by Tianma Group Corporation.
The main drafters of this standard are Wang Yufen and Liang Liusheng. This standard was first issued in 1981.
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.