Technical recommendations for metallic C(T) and SEN(B) fracture toughness test specimens: Data-driven insights from literature

• Summarises effects of specimen type, dimension, and orientation on fracture tests. • Compares C(T) and SEN(B) specimens, analysing advantages and limitations. • Analyses specimen dimension distributions and proposes recommended size ranges. The safety assessment of flawed structures is critical to ensuring their reliability and is commonly performed using Engineering Critical Assessment (ECA) or Finite Element Analysis (FEA), both of which rely on experimentally measured fracture toughness. Testing standards provide standardised methods for determining fracture toughness and regulate experimental procedures to ensure accuracy. However, standards mainly focus on procedures and data processing, offering limited guidance on specimen design, including suitability, advantages, and limitations. Although many studies have investigated factors affecting fracture toughness, systematic summaries from an experimental perspective remain limited. This study is the first to comprehensively analyse the effects of specimen type, size, and orientation on fracture toughness testing and results. Specimen orientation can reduce fracture toughness by up to 78%, while cracks in welds show a reduction of approximately 74% compared with the base material. Differences between C(T) and SEN(B) specimens are compared for the first time in terms of preparation, execution, and data processing. Larger specimens are preferable for data processing, whereas smaller specimens offer advantages in test execution, suggesting a balanced choice. A data-driven approach is employed to discuss optimal specimen dimension selection under various experimental conditions. Statistical analysis is employed to propose optimal specimen dimension ranges based on fracture toughness from 0 up to 1200 M P a m and yield strength from 200 to 1000 M P a , supporting both fracture toughness test design and structural integrity assessment.