Christian Lanvermann

Bio: Christian Lanvermann is an academic researcher from ETH Zurich. The author has contributed to research in topics: Moisture & Ultimate tensile strength. The author has an hindex of 8, co-authored 9 publications receiving 118 citations.

Combination of X-ray and digital image correlation for the analysis of moisture-induced strain in wood: opportunities and challenges

Abstract: In this present study, the moisture-induced deformation behaviour of a spruce sample was analysed one- and two-dimensionally with high resolution on the radial-tangential surface. For this purpose, an artificial speckle pattern was applied to the surface which was then recorded by a CCD camera during the deformation. The generated TIF images were analysed with a strain mapping software (VIC 2D) that computed the two-dimensional strain field from the surface deformation. Selected options to evaluate two-dimensional data generated with X-ray imaging and digital image correlation are presented. Combining and correlating these techniques enables detailed analysis of structure-function relationships during swelling (and shrinkage) processes in wood. However, several issues still have to be solved to enhance effectiveness and user-friendliness of such investigations, as elucidated in detail in this paper.

Full-field moisture induced deformation in Norway spruce: intra-ring variation of transverse swelling

Abstract: The transverse hygro-expansion of Norway spruce wood is studied on the growth ring level using digital image correlation. This non-destructive technique offers the possibility for a contactless study of 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 (LW), 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 (EW), transition wood and LW demonstrates that the radial hygro-expansion is dominated by the EW deformation, whereas tangential deformation is a complex interplay of expansion and compression that needs all tissues to fully develop.

The role of water in the behavior of wood

Abstract: Wood, due to its biological origin, has the capacity to interact with water. Sorption/desorption of moisture is accompanied with swelling/shrinkage and softening/hardening of its stiffness. The correct prediction of the behavior of wood components undergoing environmental loading requires that the moisture behavior and mechanical behavior of wood are considered in a coupled manner. We propose a comprehensive framework using a fully coupled poromechanical approach, where its multiscale implementation provides the capacity to take into account, directly, the exact geometry of the wood cellular structure, using computational homogenization. A hierarchical model is used to take into account the subcellular composite-like organization of the material. Such advanced modeling requires high resolution experimental data for the appropriate determination of inputs and for its validation. High-resolution x-ray tomography, digital image correlation, and neutron imaging are presented as valuable methods to provide the required information.

Distribution of structure and lignin within growth rings of Norway spruce

Abstract: A radial core from a Norway spruce (Picea abies (L.) Karst.) estimated to be about 107 years old was cut from a board and was analyzed for density and microfibril angle (MFA). Furthermore, cell geometry, wall thickness and lignin distribution were analyzed on three selected growth rings in detail. Intra-ring differences in the density profiles are also true for cell wall thicknesses as well as radial and tangential lumen diameters. A higher MFA was found for earlywood with a slow decrease toward the latewood region. The lignin was found to remain rather constant throughout the growth rings, which suggests a constant chemical composition of the cell wall material within the growth ring. From the recorded datasets on a cellular level, it can be concluded that the main adaptation regarding structure–property relationships toward the optimization of water transport and mechanical stability is mainly achieved at the cell level.

Combination of neutron imaging (NI) and digital image correlation (DIC) to determine intra-ring moisture variation in Norway spruce

Abstract: The hygroscopic behavior of wood has a strong influence on its mechanical performance, yet the moisture gradients within the growth ring structure have not been sufficiently investigated. The main challenge is that moisture variations are coupled with strong sample deformation, which complicates the spatial referencing of moist and dry states. In this work, neutron imaging (NI) for the detection of water and digital image correlation (DIC) for the detection of local deformation were combined to calculate the local gravimetric moisture content (MCgrav) and the volumetric moisture content (MCvol) within single growth rings. Specimens of Norway spruce [Picea abies (L.) Karst.] were exposed to an adsorption-desorption cycle, with relative humidity (RH) steps varying from 0% (oven dry) up to 95% RH. After each acclimatization step, neutron transmission and DIC images were acquired. The local deformations determined by DIC were used to assign the corresponding dry density in the undeformed state to the compartment in a moist state and thus to calculate its MC by NI. No significant MC gradients could be found between earlywood (EW) and latewood (LW) within ±0.5% accuracy. However, strong density gradients between EW and LW can be directly correlated with MCvol. It appears that the MC in the cell wall is constant regardless of the particular growth ring position.

Factors affecting the hygroexpansion of paper

Abstract: Paper is a widely used packaging material and is nowadays regaining importance, e.g., as bio-based and biodegradable material. Moreover, new technologies such as polymer–fiber composites, printed electronics and the deep drawing of paper are developing. The process stability and also the resulting quality of paper converting processes such as coating, metallization, printing, and the printing of electronics are highly affected by the hygroexpansion of paper. In order to reduce production instability and to choose and develop paper substrates with ideal characteristics, critical parameters need to be known. This paper offers an extensive overview of those parameters, starting at a molecular and microscopic level with the effect of the constituents and morphology of single fibers, before moving on to paper contents, chemical modifications and additives and finally concluding with paper production and fiber network modification. It was found that the major influences are single fiber sorption, inter-fiber contacts, microfibril angle, fiber morphology (length, width, curliness) and fiber orientation. This review gives new ideas and insights for technologists working in research, development and production optimization of paper-based products.

Non-Destructive Evaluation Techniques and What They Tell Us about Wood Property Variation

Abstract: To maximize utilization of our forest resources, detailed knowledge of wood property variation and the impacts this has on end-product performance is required at multiple scales (within and among trees, regionally). As many wood properties are difficult and time-consuming to measure our knowledge regarding their variation is often inadequate as is our understanding of their responses to genetic and silvicultural manipulation. The emergence of many non-destructive evaluation (NDE) methodologies offers the potential to greatly enhance our understanding of the forest resource; however, it is critical to recognize that any technique has its limitations and it is important to select the appropriate technique for a given application. In this review, we will discuss the following technologies for assessing wood properties both in the field: acoustics, Pilodyn, Resistograph and Rigidimeter and the lab: computer tomography (CT) scanning, DiscBot, near infrared (NIR) spectroscopy, radial sample acoustics and SilviScan. We will discuss these techniques, explore their utilization, and list applications that best suit each methodology. As an end goal, NDE technologies will help researchers worldwide characterize wood properties, develop accurate models for prediction, and utilize field equipment that can validate the predictions. The continued advancement of NDE technologies will also allow researchers to better understand the impact on wood properties on product performance.