Structural Integrity (GIE)

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The Structural Integrity Research Group (GIE) at the University of Burgos conducts research in structural assessment and design, particularly focusing on hydrogen applications as an energy vector. Its activities can be summarized in four main areas:

1. Hydrogen Research: This area investigates hydrogen as an energy vector, analysing the behaviour of materials in contact with H₂ and the embrittlement of various alloys.
2. Additive Manufacturing: The group focuses on additive manufacturing using technologies such as FDM, SLS, SLM, and Binder Jetting. This includes optimizing printing parameters, manufacturing lattice structures, and applying thermomechanical post-processing treatments to enhance mechanical properties. The impact of hydrogen on additive manufacturing is also a significant consideration in this area.
3. Material Characterization: This area encompasses characterizing materials and conducting necessary tests to study component failure, improve design, and evaluate structural integrity (including fatigue life, fracture, wear, and corrosion). The GIE group investigates different materials through static and dynamic tests, hydraulic fracture and fatigue tests (up to 6,000 bars), residual stress measurement, and metallographic and fractographic analyses.
4. Modelling Mechanical Behaviour: This area focuses on modeling the mechanical behaviour of materials under various conditions and loads. Damage and multi-physics models are developed in different finite element codes, establishing predictive tools for fracture and fatigue, including phenomena related to hydrogen embrittlement.

High Pressure and Temperature Testing Equipment in Hydrogen Environment The HPHT-H₂ (High Pressure, High Temperature, H₂ ambient) testing system features an integrated autoclave designed for high-pressure and high-temperature hydrogen environments. Its main characteristics include:

• A uniaxial testing machine capable of applying loads up to 50 kN, allowing for cyclic loading under either load or displacement control. High-frequency capacity is not prioritized, as hydrogen embrittlement is more critical at low frequencies.
• An autoclave (HPHT Cell) that can contain gaseous H₂ at pressures up to 300 bar and temperatures up to 300ºC, integrated into the testing machine to facilitate mechanical tests under specified environmental conditions. The autoclave's volume is approximately 3 liters.
• A DCPD (Direct Current Potential Drop) system for measuring deformations inside the autoclave.
• Software and controllers to automate standard tests for mechanical characterization of materials in a hydrogen environment (including Slow Strain Rate Test, Constant Extension Rate Test, Constant Load Test, and Fatigue Test) and to measure crack propagation using the DCPD method. The software also monitors pressure and temperature parameters and controls all safety systems.

Scope of Application The uniqueness of this equipment enables a wide variety of standardized tests to evaluate the mechanical properties of different materials in a high-pressure, high-temperature gaseous hydrogen environment, including tensile tests (with smooth or notched specimens), fracture tests, and fatigue tests. Below are some common tests performed with this equipment along with their corresponding standards:

1. Slow Strain Rate Test (SSRT) in a hydrogen environment (ASTM G129 or ISO 16573-2).
2. Tensile test in high-pressure and/or high-temperature hydrogen (ASTM G142).
3. Constant Load Test (CLT), where tensile specimens are subjected to a constant load until hydrogen diffusion triggers fracture (ISO 16573-1).
4. Slow Strain Rate testing in a hydrogen environment with Compact Tension (CT) specimens (ASTM G129 or ISO 11114:4-method C).
5. Test to determine the threshold for Environment-Assisted Cracking propagation (K₁H or K₁EAC) using load steps with CT specimens (ASTM E1681 or ISO 11114:4-method C).
6. Fracture toughness test (ASTM E1820) adapted for hydrogen environments with CT specimens.
7. Fatigue crack growth rate test (ASTM E647) adapted for hydrogen environments with CT specimens.

Due to the uniqueness of these tests, they must be accompanied by corresponding analyses of composition and microstructure, both before and after testing.