Introduction
In the field of materials science and engineering, composites are widely used in various industries due to their excellent properties. However, during long-term service, these materials will be subject to the synergy of environmental factors such as temperature and humidity, leading to gradual changes in performance, a process commonly known as damp-heat aging. Accurately assessing the moisture-heat aging properties of composites is crucial for predicting their service life and reliability. As an experimental equipment that simulates a specific temperature and humidity environment, the constant temperature and humidity aging chamber provides standardized test conditions for such evaluations.
Test Principle:
The basic principle of constant temperature and humidity aging testing is to create a continuous and stable accelerated aging environment for the specimen by precisely controlling the temperature and relative humidity in the closed chamber. Under high temperature and humidity conditions, water will seep into the composite through diffusion, capillary action and other mechanisms, which may lead to plasticization, hydrolysis or interfacial debonding of the resin matrix, resulting in a decrease in the mechanical, electrical, or physical properties of the material. The water diffusion process can be roughly described by Fick's second law:
∂C/∂t = D (∂²C/∂x²)
where C is the water concentration, t is the time, D is the diffusion coefficient, and x is the distance in the direction of diffusion. The test is designed to simulate and accelerate this natural aging process in order to obtain trend data on changes in material properties in a shorter period of time.
Equipment & Standards
Constant temperature and humidity aging boxes usually have high-precision temperature and humidity control systems to ensure a uniform and stable environment inside the box. When conducting tests, conditions and procedures should be set according to widely recognized technical standards at home and abroad. Common reference standards are shown in the table below:
| Standard system | Standard number and name |
| International standards | ISO 9142 Adhesives - Standard Laboratory Aging Conditions |
| Chinese standard | GB/T 2423.3 Environmental tests for electrical and electronic products - Part 2: Test methods Test Cab |
| Industry Guide | IEC 60068-2-78 Environmental testing - Part 2-78: Testing - Test Cab |
When selecting specific criteria, it is necessary to combine the practical application field of the composite material with the intended service environment.
Testing process
A complete testing process mainly includes the following steps: First, prepare a specimen that meets the dimensional requirements and conduct initial performance tests (such as mechanical strength, weight, size, etc.) as a benchmark. Subsequently, the specimen is placed in an aging chamber, the parameters are set according to the selected criteria (e.g., temperature 85°C, relative humidity 85%) and the test begins. Some specimens are taken out at set cycle points (e.g., 24h, 168h, 1000h), adjusted to equilibrium in a standard laboratory environment, and tested again. Finally, the data before and after aging were compared to analyze the performance attenuation law.
Performance evaluation indicators
To evaluate the performance changes of composite materials after wet heat aging, the following indicators are usually concerned: first, mechanical properties, such as tensile strength, flexural modulus and interlayer shear strength retention; second, physical properties, including weight change rate, dimensional stability and glass transition temperature; The third is microstructure, which can observe the changes in the interface state between the fiber and the matrix through electron microscopy. Through the comprehensive analysis of multiple indicators, the aging mechanism and durability of materials can be comprehensively understood.
Analysis and application of results
The data obtained from the test can be used to plot the change in performance metrics over time or moisture absorption. Analyzing these curves helps to understand the aging dynamics of materials, evaluate the differences in moisture and heat resistance of different material formulations, and inform product design, material selection, and life prediction. For example, a moisture absorption curve can be used to calculate the diffusion coefficient, while a strength retention curve can help determine the performance tipping point. These analysis conclusions have guiding significance for material development and quality control in aerospace, automobile manufacturing, electronics and electrical fields.
Epilogue
The use of constant temperature and humidity aging chambers for the damp heat aging performance test of composite materials is an effective and standardized evaluation method. Through rigorous test design, standardized process operation and comprehensive data analysis, it can deeply reveal the behavior of materials in humid and hot environments, providing key technical support for improving the long-term reliability and safety of composite products. With the advancement of material technology, related testing methods and evaluation systems will continue to improve.
References
1. Introduction and Principles refer to the relevant review literature on the environmental aging mechanism of polymer materials.
2. In the equipment and standards section, the standard documents listed are from the standard texts publicly released by the International Organization for Standardization (ISO), the National Standardization Administration (GB) of China and the International Electrotechnical Commission (IEC).
3. The test process and evaluation index section integrates technical guidelines and common laboratory practices for composite testing in multiple industries.