Adaptive Neutron Radiography Correlation for Simultaneous Imaging of Moisture Transport and Deformation in Hygroscopic Materials

Neutron radiography is a key non-destructive testing technology for the investigation of moisture transport in materials. However, quantitative moisture measurements in swelling materials are currently challenging due to the lack of referencing between moist and dry state radiographs. A novel adaptive texture correlation algorithm is presented to simultaneously image inhomogeneous moisture distributions and moisture-induced strain fields. The proposed method provides a valuable tool for the study of time- and position-dependent hygromechanical interactions. Moreover, it requires no modification of existing neutron installations. The method was validated against gravimetric moisture content and optic surface deformation measurements. Its applicability was demonstrated for two actual topics in wood science, the investigation of moisture gradients within the growth ring microstructure and the study of moisture transport processes in wood-fiber composites. The algorithm can be widely used to characterize hygroscopic materials with heterogeneous texture, as frequently found in wood constructions, food industry, engineering and soil science

Adaptive neutron radiography correlation for simultaneous imaging of moisture transport and deformation in hygroscopic materials

Neutron radiography is a key non-destructive testing technology for the investigation of moisture transport in materials. However, quantitative moisture measurements in swelling materials are currently challenging due to the lack of referencing between moist and dry state radiographs. A novel adaptive texture correlation algorithm is presented to simultaneously image inhomogeneous moisture distributions and moisture-induced strain fields. The proposed method provides a valuable tool for the study of time- and position-dependent hygromechanical interactions. Moreover, it requires no modification of existing neutron installations. The method was validated against gravimetric moisture content and optic surface deformation measurements. Its applicability was demonstrated for two actual topics in wood science, the investigation of moisture gradients within the growth ring microstructure and the study of moisture transport processes in wood-fiber composites. The algorithm can be widely used to characterize hygroscopic materials with heterogeneous texture, as frequently found in wood constructions, food industry, engineering and soil science

Hygromorphic response dynamics of oak: towards accelerated material characterization

When a wood board is exposed to a change in relative humidity on only one of its surfaces, e.g. in case of flooring or a panel painting, the resulting asymmetric moisture content profile induces differential expansion over the thickness. Consequently a bending moment causes the board to curve. A theory is presented to describe the bending of a wood board due to a step change in relative humidity. The board is assumed to be homogeneous, isotropic, and linearly elastic. Moisture transport is presumed to obey the diffusion equation with constant coefficients, such that moisture transport can be directly related to the bending of the board. It is shown that the transient deflective behavior provides the diffusion coefficient and the final length change yields the linear hygroscopic expansion coefficient. Derived diffusion coefficients are in good agreement with values in literature. Furthermore, a scaling law for the deflection of the board is proposed, which is seen to be followed qualitatively but not quantitatively by experiments. Finally, by assuming the deflection of the board to be the response of a linear system, the deflective frequency response of the board can be predicted from its step response. The results allow upscaling of deflection and expansion, such that behavior of thick boards can be determined from an experiment using a thin board