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Register a new userFull-field moisture induced deformation in Norway spruce: intra-ring variation of transverse swelling
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The transverse hygro-expansion of the Norway spruce wood is studied on the growth ring level using digital image correlation. This non-destructive technique offers the possibility to contactless study deformation fields of relatively large areas. The measured full-field strains are segmented into individual growth rings. Whereas radial strains closely follow the density progression with the maximum in the dense latewood, tangential and shear strain remain constant except for positions around the edges of the sample. A simple FE three phase growth ring model is in good agreement with the experimental values. The selective activation of individual phases like earlywood, transitionwood and latewood demonstrates that the radial hygro-expansion is dominated by the earlywood deformation, whereas tangential deformation is a complex interplay of expansion and compression that needs all tissues to fully develop.
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The alternating earlywood and latewood growth ring structure has a strong influence on the mechanical performance of Norway spruce. In the current study, tensile tests in the longitudinal and tangential directions were performed on a series of specimens representing one growth ring at varying relative humidities. All tested mechanical parameters, namely modulus of elasticity and ultimate tensile stress, followed the density distribution in the growth ring, with the minimum values in earlywood and the maximum values in latewood. The samples were conditioned at three the relative humidities 50%, 65% and 95%. With increasing relative humidity, the values of the mechanical parameters were found to decrease. However, due to the high local variability, this decrease was not statistically significant. The test in the tangential direction on a set of earlywood and latewood specimens at 65% relative humidity revealed a similar limit of linear elasticity for both early- and latewood. Where the strength of both tissues was equal, the strain at failure was significantly greater for earlywood. Furthermore, the portion of the non-linear stress/strain behavior for earlywood was significantly greater. A Weibull analysis on the ultimate tensile strength revealed a tissue-independent Weibull modulus, which indicates similar defect distributions. For both, the failure occurred in the middle lamella.
Ion implantation is widely used as a surrogate for neutron irradiation in the investigation of radiation damage on the properties of materials. Due to the small depth of damage, micromechanical methods must be used to extract material properties. In this work, nanoindentation has been applied to ion irradiated silicon carbide to extract radiation-induced hardening. Residual stress is evaluated using HR-EBSD, AFM swelling measurements, and a novel microcantilever relaxation technique coupled with finite element modelling. Large compressive residual stresses of several GPa are found in the irradiated material, which contribute to the significant hardening observed in nanoindentation measurements. The origin of these residual stresses and the associated hardening is the unirradiated substrate which constrains radiation swelling. Comparisons with other materials susceptible to irradiation swelling show that this effect should not be neglected in studying the effects of ion irradiation damage on mechanical properties. This constraint may also be influencing fundamental radiation defects. This has significant implications for the suitability of ion implantation as a surrogate for neutron irradiations. These results demonstrate the significance of swelling-induced residual stresses in nuclear reactor components, and the impact on structural integrity of reactor components.
The mass transfer of interstitial impurities in a crystalline lattice under the influence of the fast-moving deformation disturbance of the type of a shock wave is considered. The velocity of the movement of the disturbance is supposed to be compared with the characteristic velocity of the relaxation of the diffusion flux to its local equilibrium value determined by the Ficks law. The similar situation occurs in a number of experiments on the exposure of a solid to dynamical external loads giving rise to such fast hydrodynamical processes in a sample that the local equilibrium assumption, normally assumed for the macroscopic description of transport processes, is no longer valid. Considering the diffusion flux among the set of independent variables we have derived a set of coupled hydrodynamic equations describing nonequilibrium behavior of a solid in the absence of local equilibrium in the system. Within the scope of the proposed model it has been shown that in comparison with the local equilibrium system an enhanced mass transfer occurs under local nonequilibrium conditions.
We have performed simulations to study how increasing humidity affects the structure of Nafion-like ionomers under conditions of low sulfonate concentration and low humidity. At the onset of membrane hydration, the clusters split into smaller parts. These subsequently swell, but then maintain constant the number of sulfonates per cluster. We find that the distribution of water in low-sulfonate membranes depends strongly on the sulfonate concentration. For a relatively low sulfonate concentration, nearly all the side-chain terminal groups are within cluster formations, and the average water loading per cluster matches the water content of membrane. However, for a relatively higher sulfonate concentration the water-to-sulfonate ratio becomes non-uniform. The clusters become wetter, while the inter-cluster bridges become drier. We note the formation of unusual shells of water-rich material that surround the sulfonate clusters.
An analytical model was developped to describe the current induced DW dynamics of a Bloch DW in the presence of an external transverse magnetic field. The model takes into account the DW deformation and the magnetization tilting in the domain. The model is compared to the results of micromagnetic simulation and an excellent agreement is obtained. In the steady state regime, the model shows that the domain tilting does not change the DW mobility. An external or current induced transverse magnetic field such as the Oersted or Rashba field can prevent the Walker breakdown leading to a higher domain wall velocity.
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