Laboratory X-ray Diffraction Based Instrument for Full field Stress-Strain Measurements in Metals

Development of constitutive laws for elastic–plastic materials traditionally require hundreds of mechanical tests on statically determinate specimens to map their yield surface. Although accurate, this approach is slow and limits the pace of materials discovery, especially as modern alloy design and manufacturing accelerate while mechanical testing remains low throughput. Advanced processes such as additive manufacturing further complicate testing by producing non-uniform stress states even in nominally determinate specimens, making local mechanical response measurements essential, particularly under complex stress state incurred in most engineering applications. Digital Image Correlation (DIC) provides full-field total strain measurements and is valuable for elastic characterisation, but it cannot capture the plastic deformation fields needed to resolve history-dependent plasticity. In other words, understanding plastic behaviour requires access to an internal (history) variable beyond total strain. In this work, we address this longstanding gap by introducing a new laboratory instrument based on Energy-Dispersive X-ray Diffraction (EDXRD) that enables full field measurement of elastic strain field concurrently with DIC based full field strains to regularize the problem of constitutive modelling in metals. Consequently, we can extract local stress-strain responses along diverse loading paths (multi-axial stress states) within a single specimen, yielding dozens of independent measurements from a single test. This capability opens the door to using complex specimens (statically indeterminate) that intentionally generate a wide range of strain paths, allowing the yield surface and its evolution to be characterised from only a few experiments