Technical Analysis and Industrial Value of Prepreg Performance Testing

1. Introduction

Prepreg, as a crucial raw material for composites, plays a pivotal role in modern industrial manufacturing. It is typically made by impregnating high-performance fibers with a resin matrix, exhibiting excellent processability and stable mechanical properties. It is widely used in aerospace, wind power, automotive, marine, and sporting goods industries. Whether it's manufacturing load-bearing structures for aircraft wings or lightweight designs for wind turbine blades, the quality of prepreg directly affects the mechanical properties, durability, and manufacturing efficiency of the final products. However, due to the diversity of composites and their complex processing techniques, the stability of prepreg performance still faces numerous challenges in practical applications. Therefore, establishing a scientific and systematic set of performance testing standards is of great significance for standardizing industrial production, improving product competitiveness, and promoting technological development in the industry.

The GB/T 32788 series of standards are currently the primary technical specifications for prepreg performance testing in China, covering various indicators from processing performance to mechanical properties and material stability. These standards were formulated with reference to and modifications of ISO international standards to better suit domestic industrial needs. By measuring key properties such as gel time, resin flowability, volatile matter content, tensile strength, resin content, and mass per unit area, this series of standards establishes a comprehensive and systematic testing framework, providing a scientific basis for the production and application of prepreg. Based on the GB/T 32788 series of standards, this paper systematically analyzes the current status, significance, and future development directions of prepreg performance testing, combining testing methods and their application value.

2. Construction of the Testing Method System

The performance testing of prepreg covers multiple dimensions, including processing performance indicators reflecting the chemical behavior of the resin matrix and tests for mechanical and physical properties of the material. The GB/T 32788 series of standards have been modified and locally adapted based on ISO international standards, aiming to provide more applicable testing schemes for domestic production enterprises while ensuring that test results are internationally compatible.

The determination of gel time is an essential part of processing performance testing, directly affecting the time window and process stability of composite molding. By accurately recording the time when the resin loses its fluidity at a specific temperature, this test provides a quantitative basis for the curing process of the material. The resin flowability test evaluates the flow performance of the resin when heated, which is of great guiding significance for the molding of parts with complex geometric shapes. Especially in aerospace and wind power fields, high-flow resin can effectively wet the fibers, improving product quality. The volatile matter content test focuses on the chemical stability of the material, and the measurement results are directly related to the formation of pores during processing and the mechanical properties of the product.

The focus of mechanical performance testing is tensile strength. This indicator not only reflects the bonding strength between the fiber and the resin interface but is also an important engineering parameter in composite material design. For prepreg manufacturers, ensuring the stability of tensile strength is key to assessing product quality. Tests for resin content and mass per unit area pay more attention to the uniformity and consistency of the material, and the measurement of these indicators provides necessary basic data for the manufacture of large-size structural components.

3. Detailed Explanation and Application of Testing Methods

3.1 Determination of Gel Time

Gel time is one of the core indicators of prepreg processing performance, and its test results reflect the process of the material transitioning from a liquid to a solid state. Control of this process directly affects the efficiency and quality of the molding process. According to the GB/T 32788.1-2016 standard, the test method determines gel time by heating the sample and observing changes in its fluidity over time.

In practical applications, the determination of gel time is particularly critical in aerospace and wind power fields. For example, in aircraft skin manufacturing, the time window for the curing process is extremely strict. A too-short gel time may result in incomplete mold filling, while a too-long gel time may extend the production cycle and increase costs. In wind turbine blade manufacturing, the large size and complex shape of the blades place high demands on gel time. Through precise gel time control, manufacturers can optimize process parameters, ensuring no voids within the blades and uniform mechanical properties, thereby reducing waste rates and improving production efficiency.

3.2 Determination of Resin Flowability

Resin flowability is a key indicator reflecting the processing adaptability of prepreg. The GB/T 32788.2-2016 standard evaluates the distribution performance of resin in the mold by measuring the flow range based on the resin's ability to spread under specific temperature and pressure conditions. The test results can guide manufacturers in selecting suitable resin systems and optimizing mold design.

In actual production, the control of resin flowability is crucial for parts with complex geometric shapes. For example, C-shaped beams in the aerospace industry and multi-curved panel parts in the automotive industry require the resin to flow into every detail of the mold before curing, thereby avoiding dry fibers or bubble problems. In sports equipment manufacturing, the molding process of tennis racket frames and bicycle frames also relies on precise control of resin flowability to ensure material uniformity and mechanical properties.

3.3 Determination of Volatile Matter Content

The volatile matter content test is mainly used to evaluate the content of low-molecular-weight volatile matter in prepreg, and its results are directly related to the formation of pores during processing and the surface quality of the finished product. According to the GB/T 32788.3-2016 standard, the volatile matter content is obtained by calculating the mass loss after subjecting the test specimen to constant temperature treatment.

The volatile matter content has a significant impact on the manufacturing quality of high-performance composites. For example, in satellite antennas and aerospace structural components, high volatile matter content can lead to increased porosity during the curing process, significantly weakening the material's load-bearing capacity and fatigue performance. In automotive manufacturing, excessively high volatile matter content may affect the surface finish of parts, thereby affecting subsequent painting or bonding processes. By precisely controlling the volatile matter content, manufacturers can not only improve the mechanical properties of the product but also meet stricter environmental requirements.

3.4 Determination of Tensile Strength

Tensile strength is an important indicator for measuring the mechanical properties of prepreg. The test applies tensile load to standard-sized specimens, records the maximum stress value at the time of fracture, and operates according to the GB/T 32788.4-2016 standard. The test results provide basic data for the design and practical application of composites.

This indicator has broad significance in practical applications. For example, primary load-bearing components in the aerospace industry (such as wing beams and landing gear covers) require high tensile strength to ensure the safety and stability of components under extreme operating conditions. In the wind power industry, tensile strength data for blade structures provides theoretical support for their ability to operate long-term in strong wind environments. In the automotive industry, tensile strength testing is used to optimize crash energy absorption structural design, ensuring effective occupant protection during collisions.

3.5 Determination of Resin Content

Resin content is an important parameter determining the bonding quality between the prepreg matrix and fibers. According to the GB/T 32788.5-2016 standard, the ratio of fibers and resin is calculated by removing the resin through high-temperature burning to assess the uniformity and stability of the material.

In practical applications, the uniformity of resin content is crucial for the performance of large-size structural components. For example, in wind turbine blade manufacturing, excessively high resin content may result in insufficient local toughness, while too low resin content may affect the complete wetting of fibers, increasing the risk of blade damage. In the production of ship decks, uniform resin content can effectively prevent local stress concentration, improving component durability and fatigue resistance.

3.6 Determination of Mass Per Unit Area

Mass per unit area is an important indicator for measuring the uniformity of prepreg, and its testing is based on the GB/T 32788.6-2016 standard, which evaluates the mass distribution of prepreg by measuring the mass of a sample of a specific area. Uniform mass per unit area is crucial for the manufacture of large-size composite components.

In the aerospace industry, large skin components need to ensure the stability of mass per unit area to avoid vibration or fatigue problems caused by uneven mass distribution. In wind turbine blades, the control of mass per unit area of surface materials not only affects the overall aerodynamic performance of the blades but also determines their durability and corrosion resistance. Through testing of this indicator, manufacturers can improve the processing stability of materials, providing a guarantee for the quality of the final components.

4. Standardized Industry Value and Future Development

The GB/T 32788 series of standards provides a systematic approach to quality control for the domestic prepreg industry. By incorporating international standards, they not only meet the practical needs of the domestic industry but also lay the foundation for the international development of products. In practice, these standards have driven technological advancements among domestic prepreg manufacturers and enhanced the international competitiveness of their products. However, with the continuous progress of new material technologies and the expanding application fields, the existing standards still need further improvement in certain aspects. For instance, testing methods for thermoplastic prepregs are not yet comprehensively covered, and more sophisticated testing methods need to be developed for the performance evaluation of novel composites.

In the future, the development of prepreg performance testing will increasingly focus on automation and intelligence, with online real-time monitoring technology emerging as a trend. Additionally, with the heightened awareness of environmental protection, green testing methods and the development of low-volatility resins will also become significant directions for industry development.

5. Conclusion

The GB/T 32788 series of standards provides a scientific and systematic framework for prepreg performance testing, with the covered testing methods comprehensively reflecting key indicators from processing performance to mechanical properties of prepregs. These standards have not only played a crucial role in regulating domestic industry production but also provided strong support for the competitiveness of products in the international market. By continuously optimizing testing methods and enhancing testing accuracy and efficiency, prepreg performance testing will continue to lead the composite materials industry towards a new stage of high-quality development.