Judgment Criteria and Technical Specification for Validity of Tensile Test Data
Sep 17, 2026
Judgment Criteria and Technical Specification for Validity of Tensile Test Data
Tensile test is the most fundamental and authoritative method for evaluating mechanical properties of metallic and non-metallic materials, which obtains core indexes including yield strength, tensile strength, elongation and elastic modulus. The validity of tensile test data directly determines the accuracy of material performance evaluation, structural design basis and factory quality acceptance results. Affected by testing equipment status, specimen processing quality, operating specification, environmental fluctuation and data acquisition stability, invalid test data frequently appears in routine testing. Based on ISO 6892-1:2019, ASTM E8/E8M and domestic industrial standard systems, this document systematically defines the full-process validity judgment criteria for tensile tests, covering equipment calibration validity, specimen qualification, standardized test procedure, qualified curve characteristics, abnormal data elimination and final result confirmation, forming a standardized and executable technical judgment system for laboratory tensile data quality control.
1. General Validity Principle of Tensile Test Data
Effective tensile test data must meet the core principle of full-process standardization and true structural reflection. The test results should truly reflect the inherent mechanical properties of the material, without artificial interference, equipment deviation, specimen defects and operational errors. Any link failure including unqualified equipment, non-standard specimens, irregular operation and distorted curves will lead to data invalidation. Data validity judgment runs through the whole process of pre-test preparation, in-test execution and post-test analysis, which is a necessary procedure for test report output and quality traceability.
2. Pre-Test Validity Judgment (Basic Premise)
2.1 Testing Equipment Validity
The tensile testing machine and supporting measuring systems must be within the valid calibration period. The force measurement system shall meet Class 1 accuracy requirements specified in ISO 7500-1, with force measurement error controlled within ±1% of the indicated value; the extensometer strain measurement accuracy shall comply with ISO 9513 standard, with error not exceeding ±0.5% to ensure high-precision strain data collection . The testing machine shall complete routine verification, stiffness check and software algorithm calibration before formal testing. Equipment with overdue calibration, unstable force holding and abnormal data drift is prohibited from collecting valid test data.
2.2 Environmental Condition Compliance
Room temperature tensile tests shall be carried out under standard ambient conditions: temperature 10 ℃～35 ℃, stable humidity, no severe air flow and vibration interference. Special material tests shall strictly follow specified temperature and humidity requirements. Excessively high or low ambient temperature and continuous external vibration will cause fluctuation of test force and strain data, resulting in invalid index deviation.
2.3 Specimen Processing and Appearance Qualification
The geometric size, surface finish and machining tolerance of the test specimen shall comply with standard requirements. No obvious scratches, cracks, burrs, oxidation corrosion and processing deformation are allowed on the working section. The gauge length, width and thickness deviation shall be within the standard tolerance range. Specimens with serious surface defects, dimensional out-of-tolerance and eccentric machining cannot be used for valid data testing, as they will cause stress concentration and uneven stress distribution, leading to distorted mechanical indexes.
3. In-Test Process Validity Judgment (Core Control)
3.1 Standardized Loading Rate Control
The tensile loading rate shall be strictly implemented in accordance with ISO 6892-1 and ASTM E8 specifications. The strain rate shall be kept stable during elastic stage, yield stage and strengthening stage without sudden acceleration or deceleration. Abnormal rate fluctuation will change the material yield response and tensile fracture state, resulting in untrue strength and ductility data. Tests with irregular loading speed are automatically judged as invalid data.
3.2 Specimen Clamping and Axial Alignment
The specimen shall be clamped concentrically without obvious eccentricity, inclination and slipping during the test. Axial eccentric tension will produce additional bending stress, reduce the measured strength value and cause uneven strain distribution. Slipping between the fixture and the specimen will lead to discontinuous force values and false elongation data. Tests with eccentricity, slipping and misalignment during loading are invalid and need to be retested.
3.3 Complete Test Process
Valid tests must complete the full loading process from elastic deformation, yielding, work hardening to necking and fracture. Terminated tests due to accidental equipment failure, power failure, human collision and abnormal pause in the middle of loading are invalid. The fracture position must be located in the middle 1/3 section of the specimen gauge length; fracture near the fixture clamping section is regarded as ineffective fracture, and the data shall be eliminated.
