Interpretation of GB/T 6396-2026 Composite Steel Plate Mechanical and Process Performance Test Methods: A complete review of the key points of tensile, shear, and bending tests

In August 2026, the State Administration for Market Regulation approved the release of "GB/T 6396-2026 Composite Steel Plate Mechanical and Process Performance Test Methods" to replace the old version of the standard that had been implemented for many years.As the core testing basis for composite steel plate manufacturers, pressure vessel manufacturing companies, quality inspection agencies and third-party testing laboratories, the new standard has important adjustments in sample preparation, test equipment, data judgment and other aspects.This article starts with the three core tests of tension, shear, and bending, and systematically sorts out the key changes and implementation points of the new standard.

1. Scope of application and core revision direction of the new standard

GB/T 6396-2026 is suitable for mechanical and process performance testing of single-sided and double-sided composite steel plates, covering mainstream categories such as stainless steel composite steel plates, nickel-based alloy composite steel plates, titanium composite steel plates, copper composite steel plates, etc.Compared with the old version, the core revisions of the new standard focus on three aspects:

First, the tolerance requirements for sample preparation are unified.The old version has relatively broad provisions on the length of the parallel section and the radius of the transition arc of the tensile specimen, and the sample preparation varies greatly in different laboratories.The new standard clarifies the dimensional tolerance zone of machined specimens, requiring that the width tolerance of the parallel section be controlled within ±0.1mm. The complete bonding interface between the cladding layer and the base layer must be retained in the thickness direction, and no interface delamination caused by sample preparation is allowed.

Second, the requirements for traceability of force values of test equipment have been strengthened.The new standard clearly requires that the force measurement system of the tensile testing machine should comply with accuracy level 1 and above, and the calibration certificate should be within the validity period.For shear tests, a new requirement is added for the coaxiality of the shear fixture, and the deviation shall not exceed 5% of the specimen thickness.This means that some older equipment that has not been regularly calibrated may need to be upgraded or replaced.

Third, the criteria for determining binding performance are refined.The old version only used "shear strength not less than the specified value" as the criterion for qualification. The new standard adds descriptive requirements for the interface bonding state - if the composite layer is completely separated from the base layer after the test, even if the shear strength value reaches the standard, the interface failure mode must be noted in the report for the client to make a comprehensive judgment.

2. Tensile test: specimen clamping and loading rate are key

The tensile test of composite steel plates is different from that of single metal materials. The core difficulty lies in the large difference in mechanical properties between the cladding layer (usually thin, 1.5~6mm) and the base layer (thick, usually 6~50mm). Improper clamping can easily cause the sample to slip in the clamp or break prematurely at the clamp.

Key points for sample preparation:The new standard recommends the use of rectangular cross-section specimens. For composite steel plates with a total thickness not exceeding 30mm, full-thickness specimens can be used; when the total thickness exceeds 30mm, thinned specimens can be processed, but the thinning should be carried out from the base layer side, and the thickness of the cladding must be completely retained.There must be no scratches, rust, or work-hardened layers within the gauge length section of the specimen.

Clamping solution:It is recommended to use wedge-shaped clamps with toothed clamping surfaces. When clamping, ensure that the cladding and base layers are evenly clamped at the same time to avoid unilateral stress.For stainless steel composite panels with thin cladding, it is recommended to insert gaskets similar to the cladding material at the clamp opening to prevent the clamping teeth from directly damaging the cladding surface and causing early fracture.In our many years of composite steel plate testing services, we have found that using a combination of centered wedge clamps + custom tooth face clamps can reduce the clamp fracture rate from approximately 30% to less than 5%.

Loading rate:The new standard stipulates that strain rate control should be used before yielding, with the rate range being 0.00025/s~0.0025/s; after yielding, it can be switched to displacement control, with the rate not exceeding 1mm/min.The force-displacement curve should be continuously recorded during the test to ensure that complete yield plateau and tensile strength data are obtained.

3. Shear test: Coaxiality control directly affects data validity

Shear test is the core test item to evaluate the interface bonding quality of composite steel plates.The new standard provides more detailed provisions on the fixture design and operating procedures for shear tests.

Fixture requirements:The shearing fixture should ensure that the shearing surface is perpendicular to the axis of the specimen, and the coaxiality deviation of the upper and lower shearing dies must not exceed 0.05mm.The hardness of the clamp material should be no less than HRC55, the cutting edge should be kept sharp, and should be replaced in time when chipping or wear occurs.Currently, some general-purpose shearing fixtures on the market cannot meet this accuracy requirement. It is recommended to use special shearing fixtures specially designed for composite steel plates.

Sample size:The new standard adjusts the recommended size of shear specimens to 20mm × 20mm (square) and the thickness to the full thickness of the composite steel plate.For specimens with a thickness exceeding 25mm, it can be processed to 25mm, but it needs to be thinned from the base side.

Operation points:Before loading, it should be confirmed that the specimen and the shearing mold are completely fit and there is no hanging or deflection.The loading rate was controlled at 1~2 mm/min, and the shear force-displacement curve was continuously recorded.After the test, the interface failure pattern is observed to distinguish "shear failure" (neat separation along the joint surface) and "tear failure" (the cladding is torn). The latter usually means that the bonding strength is higher than the strength of the cladding itself, which is a sign of good bonding quality.

4. Bending test: match the diameter of the indenter with the radius of the bending center

The bending test of composite steel plates is divided into two types: inner bending (the cladding is under tension) and outer bending (the cladding is under compression). The new standard clearly distinguishes the indenter diameter and bending center radius of the two bending methods.

Inward bending test (tensile side of cladding):The diameter of the indenter should be selected based on the total thickness of the composite steel plate. When the total thickness is ≤20mm, the diameter of the indenter should be 4 times the total thickness; when the total thickness >20mm, the diameter of the indenter should be 3 times the total thickness.The bending center radius is consistent with the diameter of the indenter.The bending angle is 180°, and the cladding shall not have cracks, delamination or peeling after bending.

External bending test (compressed side of cladding):The diameter of the indenter is taken to be 2 times the total thickness, and the radius of the bending center is taken to be 1.5 times the total thickness.The bending angle is also 180°. After bending, the base layer must not have cracks, and the cladding must not have bulges or delaminations.

Equipment requirements:The bending test can be completed on a universal testing machine with a bending tooling. The testing machine should have sufficient stiffness and stroke.For large-thickness composite steel plates, it is recommended to use equipment with a force value of 100kN and above to ensure a smooth and impact-free bending process.

5. Equipment selection and transition period suggestions

The implementation of GB/T 6396-2026 places higher requirements on test equipment.Enterprises should focus on the following points when selecting and upgrading equipment:

1. Force accuracy:Ensure that the testing machine reaches level 1 and above accuracy, perform regular measurement calibration, and retain the calibration certificate.
2. Fixture configuration:Equipped with wedge-shaped tensile fixtures, special shearing fixtures for composite steel plates, and inward/outward bending fixtures to form complete testing capabilities.
3. Software features:The testing software should support real-time display of force-displacement curves, automatic data calculation, one-click generation of test reports, and be able to automatically output pass/fail conclusions in accordance with the judgment rules of the new standard.
4. Extensometer:For scenarios that require accurate measurement of yield strength and elongation, it is recommended to equip an electronic extensometer or video extensometer to improve strain measurement accuracy.

Suggestions for the transition period:There is usually a certain implementation transition period after the release of a new standard. It is recommended that enterprises complete the following tasks during the transition period: ① Organize test personnel to learn the new standard, focusing on mastering changes in sample preparation and operating procedures; ② Evaluate existing equipment to confirm whether it meets the accuracy and fixture requirements; ③ Update internal work instructions and test report templates to align with the new standards; ④ Conduct comparative tests between the old and new standards, accumulate data, and ensure the continuity and traceability of test results.

As a key material in the fields of petrochemical industry, pressure vessels, ocean engineering and other fields, composite steel plates have a direct bearing on the accuracy of mechanical property testing and the safety of engineering structures.Timely follow-up of new standard requirements, configuring compliant testing equipment, and standardizing test operation procedures are compulsory courses for every company that produces and uses composite steel plates.

If you are evaluating the upgrade plan of composite steel plate mechanical testing equipment, or need to build special testing capabilities for new standards, please contact our technical team for one-on-one equipment configuration suggestions and test method guidance.We have focused on the research and development and manufacturing of mechanical testing instruments for many years, and can provide full-process solutions from stand-alone equipment to overall laboratory planning for composite steel plates, metal materials, non-metal materials and other fields.