Principles and Applications of Poisson's Ratio Testing

Shanghai Jituo Material Technology Co., Ltd. provides Poisson's Ratio testing

In the field of material mechanics, Poisson's Ratio (symbol: ν) is a key parameter revealing the deformation characteristics of materials under stress. Its core definition is quantified by the formula: ν = - (ε_transverse / ε_axial). Here, ε_transverse refers to the transverse strain (deformation rate) of the material in the direction perpendicular to the load, while ε_axial denotes the axial strain in the direction of the load. The negative sign in the formula ensures ν is a positive value, which exactly corresponds to the intuitive deformation law of "materials contract transversely when stretched and expand transversely when compressed". This ratio is also directly related to the volume change of the material. For isotropic materials, the relationship between volume strain (θ) and axial strain can be expressed by the formula θ = ε_axial (1 - 2ν) — when ν = 0.5, θ = 0, meaning the material is an ideally incompressible substance (e.g., rubber, liquids) whose deformation only changes its shape without altering its volume; when ν < 0.5, θ ≠ 0, and most solid materials expand in volume when stretched and shrink in volume when compressed.

1. Core Principles of Poisson's Ratio Testing

The essence of Poisson's Ratio testing lies in the "synchronous and accurate measurement of axial and transverse strains". Mainstream methods are divided into two categories: static methods and dynamic methods, each corresponding to different calculation logics and standard specifications.

（1）Static Method (Quasi-Static Method)
A material testing machine applies uniaxial tensile or compressive loads to the specimen, while high-precision equipment collects strain data. Traditionally, contact extensometers were used to measure axial and transverse strains separately; nowadays, the Digital Image Correlation (DIC) method is more commonly adopted. This method involves creating a speckle pattern on the specimen surface, using cameras to capture image sequences during the loading process, and calculating full-field displacement and strain via algorithms to directly obtain ε_axial and ε_transverse. These values are then substituted into the basic Poisson's Ratio formula ν = - (ε_transverse / ε_axial) for calculation.
Core Standards:

Metallic Materials: ASTM E132-17 Standard Test Method for Poisson's Ratio at Room Temperature specifies the testing procedure for rectangular cross-section specimens, requiring measurements to be conducted in the elastic deformation stage (where stress does not exceed 50% of the yield strength) and the strain range to be controlled between 0.0005 and 0.002; GB/T 22315-2008 Metallic Materials - Test Methods for Elastic Modulus and Poisson's Ratio emphasizes that the calibration accuracy of strain gauges must reach ±1%.
Composite Materials: ISO 527-4 Plastics - Determination of Tensile Properties - Part 4: Test Conditions for Isotropic and Orthotropic Fibre-Reinforced Plastic Composites specifies that Poisson's Ratio should be calculated within the axial strain range of 0.05% to 0.25%, applicable to orthotropic materials; GB/T 3354-2014 Tensile Properties Test Method for Oriented Fiber Reinforced Polymer Matrix Composites separately defines strain measurement requirements for specimens in the 90° direction.
Concrete: ASTM C469/C469M-22 Standard Test Method for Static Modulus of Elasticity and Poisson's Ratio of Concrete in Compression uses cylindrical specimens, determining Poisson's Ratio at the stress level corresponding to 40% of the compressive strength; GB/T 50081-2019 Standard Test Methods for Physical and Mechanical Properties of Concrete adds a testing protocol for prismatic specimens, requiring the transverse strain measurement accuracy to reach ±0.0001 strain.

（2）Dynamic Method (Acoustic/Ultrasonic Method)
Based on the principle that "the propagation speed of elastic waves is related to the elastic constants of materials", this method uses equipment to measure the propagation speeds of longitudinal waves (V_L) and shear waves (V_S) in the specimen. Combined with the material density (ρ), Poisson's Ratio is calculated. The core calculation formula is ν = [1 - 2(V_S / V_L)²] / [2 - 2(V_S / V_L)²]; alternatively, the elastic modulus (E) and shear modulus (G) can first be derived from wave speeds and density, then substituted into the correlation formula ν = (E / (2G)) - 1 for deduction.
Core Standards:

ASTM E494-15 Standard Test Method for Dynamic Young’s Modulus, Shear Modulus, and Poisson’s Ratio by Impulse Excitation of Vibration specifies that the measurement accuracy of longitudinal/shear wave speeds must reach ±0.5%, applicable to homogeneous materials such as metals and ceramics.
GB/T 45598-2025 Fine Ceramics - Test Method for Dynamic Young's Modulus, Shear Modulus and Poisson's Ratio at Elevated Temperatures by Impulse Excitation Method is the first domestically developed standard in China. It adopts high-temperature vibration frequency testing technology (applicable up to 1200°C), calculating Poisson's Ratio based on bending and torsional vibration frequencies, and is particularly suitable for non-destructive testing of ceramic components in aero-engines.

2. Practical Applications of Poisson's Ratio Testing

The value of Poisson's Ratio testing runs through the entire process of material research and development as well as engineering applications, and its calculation results, together with standard specifications, form the basis for decision-making.

（1）Structural Design and Simulation

In Finite Element Analysis (FEA), the standard value of Poisson's Ratio directly affects simulation accuracy. For example:

The design of building steel structures must comply with GB/T 22315 and adopt a steel parameter of ν ≈ 0.3 to ensure the accuracy of lateral expansion simulation for compressed columns;
The simulation of concrete bridges must be based on the Poisson's Ratio of concrete in the elastic stage specified in ASTM C469 (usually ν ≈ 0.2) to avoid overestimating the structural deformation reserve capacity.

（2）Material Selection and Standard Compliance

The requirements for material deformation characteristics in different scenarios are quantified through standard testing:

Gasket materials must meet the testing requirements for rubber-like materials in ISO 527-1 (ν ≈ 0.49) to ensure volume stability during compression;
Aerospace composite components must verify the difference in Poisson's Ratio between orthogonal directions (e.g., ν ≈ 0.2 in the 0° direction, ν ≈ 0.5 in the 90° direction) through GB/T 3354 to optimize the design of laminated structures.

（3）Research on Special Materials and Standard Innovation

Research on "auxetic materials" (ν < 0) has promoted the expansion of testing standards. By improving the strain measurement accuracy of ASTM E132 (up to ±0.00001), accurate characterization of the negative Poisson's Ratio effect in metal matrix composites has been achieved. The application of such materials in intelligent defense skins must simultaneously meet the non-destructive testing requirements of the dynamic method (ASTM E494).

（4）Quality Control and Standard Compliance Verification

The standard deviation of Poisson's Ratio is a sensitive indicator of material defects:

If the measured ν value of a metal plate is more than 5% lower than the value specified in GB/T 22315, it may indicate internal fatigue cracks;
Changes in the ν value of ceramic materials at high temperatures must be monitored using the impulse excitation method in GB/T 45598 to ensure the service safety of turbine blades.

3. Development and Trends of the Standard System

Poisson's Ratio testing standards are evolving toward material specialization and extreme environmental adaptability. At the international level, the ISO 527 series and ASTM standards complement each other (e.g., ISO 527-4 focuses on the anisotropy of composite materials, while ASTM E132 concentrates on the room-temperature performance of metals); domestic standards, on the other hand, emphasize engineering applicability, such as the detailed regulations on the curing conditions of concrete test blocks in GB/T 50081. Emerging fields like 3D printing materials are driving the expansion of dynamic method standards toward non-homogeneous material testing. Through the combination of DIC technology and ultrasonic methods, synchronous characterization of full-field strain and elastic constants has been realized.

In summary, Poisson's Ratio testing standards serve as a key link connecting theoretical formulas and engineering practice. Their accurate application not only ensures the consistency of material performance evaluation but also promotes the standardization process of high-end equipment research and development and new material innovation.