JJG 139-2017, “Verification Procedure for Tensile, Compression, and Universal Testing Machines,” has a clear scope of application, covering initial verification, subsequent verification, and in-use inspections of tensile, compression, and universal testing machines. This procedure is crucial for ensuring the accuracy and reliability of testing machines.

In modern industrial production and scientific research, tensile, compression, and universal testing machines are widely used in fields such as material mechanical property testing and product quality inspection. For example, in mechanical property testing such as tension, compression, and bending of metals, non-metallic materials, and composite materials, the accuracy of the test results is directly affected by the precision and stability of the testing machine.

The scope of application of JJG 139-2017 ensures that all types of testing machines receive standardized calibration at different stages. Initial calibration is a comprehensive test of newly manufactured testing machines to determine whether they meet design requirements and relevant standards. Subsequent calibration is conducted after the testing machine has been in use for a certain period of time to ensure that its performance remains within the specified range. In-use inspection monitors the testing machine’s status during daily use to promptly identify and resolve any potential problems.

By clearly defining the scope of application, JJG 139-2017 provides unified standards and specifications for the calibration of testing machines, which helps improve the quality and reliability of testing machines and provide accurate and reliable test data for industrial production and scientific research.

2. Detailed explanation of the regulations

(1) Preparation before verification

Pre-calibration preparation is crucial, as it directly impacts the accuracy and reliability of subsequent calibration results. First, carefully inspect the testing machine’s exterior to ensure it is free of visible damage or deformation. Verify that all components, such as sensors and fixtures, are securely connected. Also, check that auxiliary equipment, such as the power supply, air supply, or hydraulic pressure, is functioning properly.

According to the verification procedures, prepare the necessary tools and equipment, such as standard weights, a dynamometer, a hardness tester, a steel ruler, and a vernier caliper. Inspect the verification standards and samples to ensure they meet the requirements and record the relevant information. Before verification, adjust the testing machine’s zero point and sensitivity to ensure the accuracy of the test results. Prepare the necessary record forms and documentation to record the verification data and results.

(2) Calibration requirements

Calibration is crucial for ensuring the accuracy of testing machines. Testing machines should be accurately calibrated according to specified standards, such as JJG 139-2017, “Verification Procedure for Tensile, Compression, and Universal Testing Machines.” During calibration, the correct test parameters, including loading rate and test temperature, must be used. Appropriate controls must also be implemented to ensure stable operation of the testing machine throughout the test.

For example, universal testing machines with a measurement range of 10N to 3000kN and an accuracy level of Class 1 or below must be calibrated strictly according to verification procedures. Functional testing involves testing various functions of the testing machine, including load capacity, displacement, and deformation. These tests must comply with international standards and relevant regulations. Precision testing involves testing the machine’s accuracy, including control accuracy and load accuracy, to ensure compliance with specified standards.

(3) Error correction

During the calibration process, it is crucial to promptly correct the errors of the universal testing machine. For mechanical errors, such as excessive friction, adjust the guide wheel clearance to eliminate friction and, if necessary, clean the hydraulic cylinder. For electronic component precision errors, such as positive deviations from the indicated value, after confirming that the instrument’s installation level meets regulatory requirements, loosen the fastening screws connecting the rocker arm and push plate in the force measuring section (reading mechanism) to the bushing. Adjust the push plate inward, tighten the fastening screws, and then perform a step-by-step calibration using the small dial. Repeat this process several times until the calibration passes. If the small dial passes but the large and medium dials still exceed tolerance, increase the weight of thallium B and thallium C appropriately until the calibration passes.

If the indicated value is negatively deviating from the tolerance, first check that the force-measuring piston is correctly installed and that the friction is excessive. Once this is eliminated, adjust the push plate outward and adjust the small dial to meet the tolerance. If the large and medium dials are still out of tolerance, appropriately reduce the weight of thalliums B and C until the calibration passes. If the indicated value error appears as “positive in front and negative in back” or “negative in front and positive in back” on the dial, and individual points are out of tolerance, adjust the angle of the contact surface between the push plate and the gear rod head by placing copper or other thin metal sheets between the steel plate and the push plate. Repeat the calibration and adjustment until the calibration passes.

(4) Regular inspection and maintenance

Regular inspections of instrument components are crucial for ensuring proper operation and extending the lifespan of testing machines. Regular inspections include daily inspections, periodic comprehensive inspections, and specialized inspections. Daily checks should be conducted to monitor equipment operating conditions, including appearance, temperature, and sound levels, to promptly identify any abnormalities. Comprehensive inspections should be conducted at prescribed intervals, including internal structure and component wear. Targeted specialized inspections should be conducted based on equipment characteristics and operating conditions. Wearing parts should be inspected and replaced promptly to prevent equipment failure.

Damaged or deteriorated parts should be promptly replaced to maintain the proper function of the instrument. Contamination and wear should also be prevented, for example, by keeping the testing machine’s operating environment clean and free from dust, oil, and other contaminants. The sensors in the rubber pad static stiffness test equipment should be regularly calibrated to ensure accuracy. Standard force gauges should also be subject to enhanced supervision and maintenance, including confirmation after each handling, regular and irregular inspections, and annual repeatability and stability testing in accordance with the 1033 Metrology Standard Assessment Specifications to ensure the accuracy and reliability of metrological verification data.

3. Differences from the old version

(1) Scope of application

The previous version of the regulations had a relatively narrow scope of application, primarily targeting specific types of tensile, compressive, and universal testing machines. JJG 139-2017, on the other hand, has a broader scope, encompassing not only the testing machines defined in the previous version but also small-load material testing machines and micro-force testing machines covered by the previous version of JJG 157-2008, as well as testing machines for leather, paper, rubber, plastics, and fibers. Furthermore, electronic tensile and compressive testing machines and electro-hydraulic servo tensile and compressive testing machines with closed-loop control are calibrated according to specialized regulations, while this regulation applies to testing machines with open-loop control.

(2) Definition of terms

JJG 139-2017 has made some adjustments and improvements to terminology. For example, the definitions of “suspended glass curtain wall” and “hanging clamp” have been revised, and mechanical properties have been added. It is now clarified that hanging clamps for suspended glass curtain walls are composite components used to hang and install glass panels or ribs, transferring the gravity load of the glass panels or ribs to the supporting structure or main structure.

(3) Inspection items

In the old version of the regulations, the technical requirements for pendulum force testing machines were gradually phased out. With the introduction of electronic force measurement, JJG 139-2017 added requirements for zero drift. Given that some testing machines use the displacement of a moving crossbeam to indicate specimen deformation when testing non-metallic materials, the new version of the regulations adds requirements for displacement measurement. Furthermore, while some current testing machines utilize open-loop control, they also include deformation measurement devices. For testing machines equipped with extensometers, extensometer calibration is conducted in accordance with JJG 762. Test force retention is no longer based on the testing machine’s classification requirements, but is now standardized at 0.2% FS. Requirements for friction between the cylinder and piston of hydraulic testing machines have been added to the general technical requirements. In accordance with GBT 3159-2008, the insulation resistance requirement has been changed from no less than 2 MΩ to no less than 1 MΩ. The coaxiality requirement has been updated to include a method for measuring geometric coaxiality for forces below 30 kN. The requirement for a force threshold for testing machines has been removed. Added requirements for selecting force verification points for testing machines without gears.

(4) Quality assurance information

JJG 139-2017 also introduces some changes to quality assurance documentation. For example, product inspection is divided into factory inspection and type inspection. Factory inspection items include appearance, dimensions, and allowable deviations. Products from the same batch of raw materials, specifications, and models are considered a batch of 1,000 sets. Quantities less than 1,000 sets are counted as one batch. Appearance inspection is performed on all units. Units that fail to meet the requirements are deemed unqualified. The normal inspection secondary sampling plan outlined in GB/T 2828.1-2012 is adopted, with an inspection level of I and an acceptance quality limit (AQL) of 6.5. Screw quality inspection should be conducted in accordance with CBT 93, G+6, and 197-2003. Surface corrosion resistance testing should be conducted in accordance with GB/T 0125. The test method for perforated lifting clamps should be conducted in accordance with Appendix D.

4. Interpretation of Important Terms

(1) Surface roughness requirements

In JJG 139-2017, surface roughness requirements significantly impact the performance and accuracy of testing machines. Typical coating systems typically require a roughness of 40 to 75 microns (Rz). Surface roughness after blast cleaning of steel can be qualitatively characterized by shape and size. Surface roughness assessment criteria include hy (maximum height from peak to valley within the sampling length, ISO 8503-3), Ry (maximum height from peak to valley within the sampling length, ISO 8503-4), and Ra (average distance from peaks and valleys to an imaginary centerline, ISO 3274). An appropriate surface roughness increases the surface area of ​​the testing machine, providing more anchor points for the coating system. However, a higher surface roughness is not necessarily better, as the coating must be able to cover these roughness peaks. Excessive roughness increases coating consumption.

(2) Contact area requirements between the clamp plate and the glass

JJG 139-2017 also specifies the contact surface area between the clamp plate and the glass. Specifically, the contact area between a single backing plate of a clamp-type clamp and the glass must be no less than 48mm x 160mm; the notch depth of a perforated clamp must be no less than 95mm. These requirements ensure that the clamp can stably clamp the glass panel or rib during use, effectively transferring gravity loads to the supporting structure or main structure. Strict adherence to these contact surface area requirements improves the load-bearing capacity and safety of the clamp, reducing the occurrence of problems such as localized excessive stress and glass breakage caused by insufficient contact area.

In short, JJG 139-2017 has important significance and value in the field of testing machine calibration. In the future, it will play a greater role in intelligence, new materials, etc., and provide more accurate and reliable test data for industrial production and scientific research.