Interpretation of Performance Requirements and Testing Standards for Composites Used in Ocean Engineering

Ocean engineering is a vital field for global energy development and technological advancement, encompassing various application scenarios such as deep-sea mining, offshore wind power, and floating platforms. Due to the complex and variable marine environment, composites must meet multiple performance requirements such as high strength, corrosion resistance, and lightweighting. They must also endure long-term exposure to salt spray, high humidity, ultraviolet radiation, and temperature differences. This article provides a detailed interpretation of the design and verification logic of composites for ocean engineering from the perspectives of performance requirements and testing standards, offering systematic support for industry development.

Interpretation of Performance Requirements and Testing Standards for Composites Used in Ocean Engineering

1. Core Performance Requirements

The performance requirements for composites in ocean engineering are mainly divided into three dimensions: mechanical properties, environmental durability, and functional characteristics, each encompassing multiple specific indicators. The following is a detailed analysis of each dimension.

1.1 Mechanical Properties

Composites in ocean engineering must withstand extreme mechanical loads, with strength and stiffness being fundamental requirements. The following is an analysis of key mechanical property indicators.

1. Bulk Density

Bulk density directly affects the buoyancy balance and lightweight design capabilities of materials. For marine equipment, bulk density typically needs to be controlled within the range of 0.5-1.8 g/cm³. Lower density allows materials to meet strength requirements while reducing equipment weight. The ASTM D1622-20 testing standard can accurately measure the bulk density of composites and ensure they meet engineering design requirements.

2. Compressive Strength and Compressive Modulus

Compressive strength determines the stability of materials under axial loads, while the compressive modulus reflects their deformation resistance. In deep-sea operations, equipment must withstand high hydrostatic pressure for extended periods, with compressive strength typically requiring over 500 MPa and a compressive modulus of over 40 GPa. ASTM D695-15 provides a standardized testing method to measure the compressive strength and modulus of materials through axial loading, providing a basis for structural design in high-pressure environments.

3. Flexural Modulus

The flexural modulus is an indicator of a material's bending stiffness under complex loading conditions, especially for floating platform support structures and wind turbine blades, where the flexural modulus is required to reach 25-50 GPa. The three-point or four-point bending test method according to ASTM D790-17 can effectively assess the bending performance of composites and verify their structural stability in applications.

1.2 Environmental Durability

The high salinity, high humidity, and intense ultraviolet radiation in the marine environment make environmental durability a core requirement for composite design. The following is an analysis of key environmental performance indicators.

1. Water Absorption

Long-term water absorption can degrade the mechanical properties and structural integrity of composites, so the water absorption rate of materials must be strictly controlled below 0.5%. The MIL-S-2415A standard assesses the water absorption behavior of materials and its impact on performance through constant-temperature seawater immersion tests combined with weight change rates.

2. Salt Spray Resistance

High salt concentrations in the marine environment can accelerate surface corrosion and delamination of materials. The salt spray test (ASTM B117) simulates corrosive environments and combines mechanical performance tests to verify whether the strength retention rate of materials after salt spray exposure is below 5%.

3. UV Aging

Marine facilities are exposed to ultraviolet radiation for extended periods, requiring material surfaces to remain stable without significant degradation. ISO 4892-2 assesses the photodegradation characteristics of composites by simulating UV radiation and combining yellowing index and mechanical property change rates.

1.3 Functional Characteristics

The functional characteristics of composites in ocean engineering must meet specific environmental requirements, including flame retardancy and electrical insulation.

1. Flame Retardancy

In marine platforms and shipping operations, fire risks impose strict requirements on the flame retardancy of materials. UL94 V-0 ensures safety in fire situations by evaluating the flame spread and extinguishment time after ignition.

2. Electrical Insulation

Composites in submarine communication equipment and power transmission devices must exhibit excellent insulation properties. ASTM D257 assesses the electrical safety of materials in humid environments by measuring surface and volume resistivity.

2. Analysis of Testing Standards and Methods

Internationally recognized testing standards provide a scientific basis for the performance verification of composites, with each performance indicator corresponding to specific testing methods. The following provides a detailed analysis from the perspectives of mechanical properties, environmental durability, and functional characteristics.

2.1 Mechanical Property Testing

Mechanical property testing of composites includes bulk density, compressive strength, flexural modulus, and shear strength tests.

1. Bulk Density Testing (ASTM D1622-20)

Bulk density testing calculates the density of materials by precisely measuring the volume and weight of samples. This test is applicable to both single composites and the assessment of the impact of different fiber/matrix ratios on density, serving as a fundamental tool for lightweight design.

2. Compressive Property Testing (ASTM D695-15)

Compressive testing uses cylindrical or cubic samples, applying axial loading until failure to record compressive strength and modulus. This test is widely used for assessing shell materials of deep-sea equipment, simulating actual loading scenarios in operations.

3. Flexural Property Testing (ASTM D790-17)

The three-point or four-point bending loading method is used to determine the flexural strength and modulus of materials. This method is particularly suitable for verifying the bending stiffness of structural materials for wind turbine blades and floating platforms.

2.2 Environmental Adaptability Testing

Environmental adaptability testing assesses the long-term stability of materials in complex marine environments.

1. Water Absorption Testing (MIL-S-2415A)

Material samples are immersed in constant-temperature seawater, with regular weighing to record water absorption, combined with changes in mechanical properties, to assess the impact of water absorption on the overall performance of materials.

2. Salt Spray Corrosion Testing (ASTM B117)

Salt spray corrosion testing exposes materials to high-salt concentration environments and combines subsequent mechanical performance tests to verify their corrosion resistance.

3. UV Aging Testing (ISO 4892-2)

UV aging testing simulates UV radiation using lamps, combining the yellowing index and mechanical property degradation of material surfaces to assess their resistance to photodegradation.

2.3 Functional Performance Testing

Functional performance testing focuses on the adaptability and reliability of materials in specific environments.

1. Flame Retardancy Testing (UL94 V-0)

Vertical burning tests assess the extinguishment time and flame spread rate of materials after ignition, providing fire safety assurance for marine platforms and shipping applications.

2. Electrical Insulation Testing (ASTM D257)

The surface and volume resistivity of materials are measured in humid environments to verify their electrical safety in submarine communication equipment.

3. Conclusion and Outlook

Composites used in ocean engineering must possess excellent mechanical properties, environmental durability, and functional characteristics to meet complex and varied operational requirements. Comprehensive performance assessment and verification of composites through internationally recognized testing standards can effectively guide material design and optimization. In the future, with the intelligent and digital development of testing technology, material performance verification will become more efficient and precise, providing a solid foundation for the sustainable development of ocean engineering.