1、 Overview of the verification during testing machine

Generally speaking, the effective period of material testing machine verification / calibration is one year. Besides the verification / calibration plan, the intermediate verification plan should be prepared according to the state of the testing machine. For the testing machine which is frequently used, it is recommended to conduct two or more intermediate checks during the verification period. If it is less used, the verification interval can also be extended. In addition, the testing machine with the following characteristics needs to be periodically checked:

(1) For testing machines newly purchased or replaced with main functional modules, intermediate verification shall be conducted between the first and subsequent verification / calibration cycles.

(2) The force value of electronic or microcomputer controlled testing machine drifts, which is quite different from the theoretical judgment.

(3) It is a testing machine with high frequency.

(4) Especially important tests will be carried out, and the results will be measured by the more important testing machine.

2、 Comparison of verification methods

1. Transfer comparison method

Combined with the relevant regulations of the testing machine, the standard dynamometer and force value weight are mainly used to verify the test force.

(1) Force value weight method

This method is mainly used in 5kn and below tensile testing machine. No matter what level the testing machine is, the following points should be considered when selecting force value weight for intermediate verification

① Technical index requirements of special weights MPE: ± 0.1%。

② Whether the structure space of the weight hanging on the testing machine meets the requirements.

③ Whether the weight force value is within the verification / calibration measurement range of the testing machine.

The force value weight method has the advantages of high accuracy, good stability and simple operation, which is suitable for the Period Verification of small force value tensile testing machine.

2. Comparison method

Comparison is a common method for quality control and capability verification in laboratory. Although the purposes of interim verification and result quality control are different, if the stability of the selected test sample / verification standard is good enough, the method of result quality control can be used for interim verification. For the testing machine, it can be divided into the comparison of the testing machine itself, the comparison between multiple testing machines and the comparison between laboratories.

3. Verification standard method

The verification standard of testing machine shall have the following characteristics:

(1) With a certain accuracy level, it is better to select the dynamometer with the same level as the verification testing machine.

(2) It has enough resolution to reflect the change of the last digit of the force value parameter display of the verification testing machine.

(3) Its metrological performance is relatively stable and repeatable.

At present, the accuracy level of domestic material testing machines is mostly level 1, and some of them are level 0.5 in universities and national defense science and engineering fields. Therefore, for the verification standard of testing machine, the working force measuring instrument with accuracy level of 1.0 can be selected, such as force measuring ring, load sensor, etc. According to the economic evaluation, when the range of the verification testing machine is less than 1000KN, the working force measuring ring can be selected; When the testing machine is 1000KN or above, the strain type dynamometer such as load sensor can be selected.

4. Retention sample retest method

The following problems should be paid attention to when selecting retention sample retest method for interim verification:

(1) The selection of retention samples. The mechanical properties of retained samples must be uniform and stable. During the period of verification, all samples in the plan must be the same batch of samples, and the uniformity and stability of samples shall meet the requirements of GB 1499.2-2007 steel for reinforced concrete Part 2 hot rolled ribbed bars. For example, the standard concrete sample (pressing direction) and the standard steel sample (pulling direction) are required to be the same manufacturer, batch and specification, and it is better to take several sections on the same root (section) as the reserved samples.

(2) The environmental conditions for sample preservation must be strictly controlled to ensure that the sample is stable and reliable, and the performance cannot be greatly changed.

(3) The measurement method, personnel, site, equipment and verification items of each interim verification shall be strictly consistent.

(4) After the verification / calibration of the testing machine, the first test of intermediate verification is carried out immediately, and the test value is taken as the reference value.