Soren Ostlund

KTH Royal Institute of Technology | KTH · Department of Engineering Mechanics

We introduce a three-dimensional geometrically nonlinear Reissner beam theory with embedded strong discontinuities for the modeling of failure in structures and discuss its finite element implementation. Existing embedded beam theories are geometrically linear or two-dimensional, motivating the need for the present work. We propose a geometrically...

Adhesion is crucial for the development of mechanical properties in fibre-network materials, such as paper or other cellulose fibre biocomposites. The stress transfer within the network is possible through the fibre–fibre joints, which develop their strength during drying. Model surfaces are useful for studying the adhesive strength of joints by ex...

We investigate the compressive failure mechanisms in flax fiber composites, a promising eco-friendly alternative to synthetic composite materials, both numerically and experimentally, and explain their low compressive-compared-to-tensile strength, the compressive-to-tensile strength ratio being 0.28−0.6. We present a novel thermodynamically consist...

The present study investigates torsional and compressive loading of a paperboard package. Finite element (FE) analyses simulating the tests were performed to improve understanding of the stresses and deformations in the paperboard during loading. A simple experimental characterization of the necessary material properties could be performed to repre...

High alkali impregnation (HAI) increases the total yield of softwood pulps following kraft cooking. This yield improvement is also maintained after oxygen delignification. This study evaluates how bleaching with either chlorine dioxide or hydrogen peroxide affects the final yield of samples obtained with standard and HAI. The chemical composition,...

The computational analysis of fiber network fracture is an emerging field with application to paper, rubber-like materials, hydrogels, soft biological tissue, and composites. Fiber networks are often described as probabilistic structures of interacting one-dimensional elements, such as truss-bars and beams. Failure may then be modeled as strong dis...

Hot-pressed, binder-free wood fiber (WF) composites can serve as load-bearing and eco-friendly materials, and the comparison of nanoscale fibril reinforcement with microscale wood fibers is of interest. We investigated property differences and interpret deformation mechanisms with strain field measurements using digital image correlation combined w...

This study investigated whether the yield improvement after high alkali impregnation (HAI) is maintained after oxygen delignification and whether the potential of oxygen delignification to increase the mechanical properties is affected by high alkali impregnation. The yield improvement achieved by high alkali impregnation (1 %) was preserved after...

Little is known about fracture toughness of monomer-impregnated wood biocomposites, with no data for transparent wood. For building applications, toughness is important, but the anisotropic nature of wood generates complex stress distributions that needs to be accounted for. A four-point bending fracture mechanics test is combined with digital imag...

The computational analysis of fiber network fracture is an emerging field with application to paper, rubber-like materials, hydrogels, soft biological tissue, and composites. Fiber networks are often described as probabilistic structures of interacting one-dimensional elements, such as truss-bars and beams. Failure may then be modeled as strong dis...

To model fiber failures in random fiber networks, we have developed an elastoplastic Timoshenko beam finite element with embedded discontinuities. The method is based on the theory of strong discontinuities where the generalized displacement field is enhanced by a jump. The continuum mechanics formulation accounts for a fracture process zone and a...

Creasing is an essential process to convert paperboards into packages since it enables folding along well-defined lines. The creasing process relies on purpose-made damage that is initiated in the paperboard structure: delamination. However, creasing might also cause in-plane cracks, which must be avoided. In this laboratory study, three paperboard...

Large deformations under in-plane compression of paperboard appear in forming processes like hydroforming, pressforming and deep drawing, but the mechanisms of deformation have not been studied on a micromechanical level. A constrained in-plane compression test is presented. This test allows for in-plane compression, buckling, wrinkling and compact...

Charged groups in pulp have been shown to enhance the tensile strength of the paper produced from the pulp. Oxygen delignification introduces charged groups and it is of interest to determine how the delignification should be distributed between the cooking and the oxygen stage with respect to mechanical properties. A number of unbleached kraft coo...

The fiber properties after oxygen delignification and kraft pulping were studied by looking into the chemical characteristics and morphology. The effect of the two processes on the fibers was evaluated and compared over a wider kappa number range (from 62 down to15). Wide-angle X-ray scattering, nuclear magnetic resonance and fiber saturation point...

Finite element (FE) analyses can be used as a powerful tool in the package design process to study for instance stress and strain fields that arise during loading. An orthotropic linear elastic material model with a stress‐based failure criterion was used to simulate box compression tests (BCTs) of a paperboard package in the FE solver LS‐Dyna. Phy...

The potential of modifying pulp and paper properties by oxygen delignification was assessed by looking beyond the ordinary purpose of oxygen delignification. Pulps with the same kappa number were obtained by both pulping and combined pulping and oxygen delignification and the mechanical and chemical properties were compared. The oxidation of pulp c...

To verify a linear relation between normalized mechanical property and moisture ratio, in-plane tensile tests were performed on four types of paperboard from different manufacturers. Tensile properties were normalized with respect to the property at standard climate (50 % RH, 23°C). Short-span Compression Tests were also performed to investigate if...

In this study, the back calculated compressive properties of flax fibers utilizing the Impregnated Fiber Bundle Test (IFBT) were investigated. The back calculated stress-strain response can be described by the Ramberg-Osgood model. The back calculated compressive modulus of the fiber is similar to its back calculated tensile modulus. The compressiv...

Five commercial multiply folding boxboards made on the same paperboard machine have been analyzed. The paperboards were from the same product series but had different grammage (235, 255, 270, 315, 340 g/m2) and different bending stiffness. The paperboards are normally used to make packages, and because the bending stiffness and grammage varies, the...

Transparent wood (TW) based on delignified birch veneer and thermoplastic poly(methyl methacrylate) (PMMA) is investigated by uniaxial tensile tests and full-field strain analyses based on digital image correlation techniques. TW is considered as a composite of unidirectional fibers (wood veneer) in a matrix (PMMA). Four in-plane elastic constants...

Compression failure by fiber kinking limits the structural applications of fiber composites. Fiber kinking is especially prevalent in laminates with holes and cutouts. The latter behavior is characterized by strain localization in the matrix material and fiber rotations. To study fiber kinking on the level of the individual constituents, a homogeni...

Motivated by sustainability arguments there is a recent interest in forming of advanced structures in paper and paperboard. Therefore, in this paper, hydro-forming of papers and the effect of different fibre raw materials, beating, strength additives (PVAm), grammage and wet and dry papers have been investigated experimentally and numerically. The...

There is a large potential for wood-fibre based materials such as paper and board to contribute to lightweight structures in several applications, particularly packaging. Fibre-based packaging materials have important advantages in comparison to fossil-based plastics regarding biodegradability, recyclability and renewability. Individualisation has...

Motivated by sustainability arguments there is a recent interest in forming of advanced structures in paper and paperboard. Therefore, in this paper, hydro-forming of papers and the effect of different fibre raw materials, beating, strength additives (PVAm), grammage and wet and dry papers have been investigated experimentally and numerically. The...

This data article contains the dynamic mechanical thermal analysis (DMTA) results for sheets made from cellulose fibers partially converted to dialcohol cellulose as presented in “Advanced Three-Dimensional Paper Structures: Mechanical Characterization and Forming of Sheets Made from Modified Cellulose Fibers” by Linvill et al. [1]. See Larsson and...

A simple, one-dimensional model for perfectly plastic hinges, utilizing a hinge yield strength, was applied to wrinkled paperboard and validated. The hinge model was incorporated into a three-dimensional constitutive model of paperboard including wrinkle initiation, wrinkle compression, as well as tensile re-loading of wrinkled paperboard. The cons...

Cellulose partially converted to dialcohol cellulose has been identified as a potential breakthrough material for the production of bio-based, complex, double-curved surfaces due to its extensive strain-at-break characteristics (reaching as great as 80 % in tensile loading). Tensile testing of handsheets made from modified cellulose fibers was cond...

Paperboard is oftentimes subjected to biaxial in-plane stress and strain states, although very few experimental studies of the biaxial in-plane yield and failure of paperboard have been conducted. A new biaxial testing method to determine the in-plane stress- and strain-based yield and failure surface of paperboard was proposed and implemented. The...

High density cellulose-based materials have been widely used for electrical insulation and (interior) construction or structural material. Similar to typical paper/board materials, the microstructure of high-density fibre mats consists of a porous network of cellulose fibres, which contributes to its highly non-linear mechanical response. Such fibr...

A moisture-dependent and temperature-dependent constitutive model for paper materials was proposed and implemented into a finite element model of the paper hydroforming process. Experimental hydroforming was conducted at temperatures of 23°C and 110 °C and moisture contents of 6.9 and 10.6 (respectively corresponding to 50 and 80% relative humidity...

Explicit finite element simulations have been utilized to identify key parameters in various 3-D forming methods for paper and paperboard. In order to compete with plastic-based packaging, new manufacturing methods (including both sliding blank and fixed blank methods) are being introduced to form complex, 3-D, paperboard shapes, including hydrofor...

Abstract An explicit finite element model of the deep-drawing of paperboard has been developed utilizing a custom yet simple material model which describes the anisotropy and plasticity of paperboard. The model was verified with a variety of tests and was then utilized to compare the punch force that was measured during the deep-drawing experiments...

A continuum material model is developed for simulating the mechanical response of high-density cellulose-based materials subjected to stationary and transient loading. The model is formulated in an infinitesimal strain framework, where the total strain is decomposed into elastic and plastic parts. The model adopts a standard linear viscoelastic sol...

To model advanced 3-D forming strategies for paper materials, the effects of environmental conditions on the mechanical behavior must be quantitatively and qualitatively understood. A tensile test method has been created, verified, and implemented to test paper at various moisture content and temperature levels. Testing results for one type of pape...

Corrugated package designers are focused on balancing the need for product protection, material use efficiency and the packaging material's impact on the environment in the supply chain. The purpose of this paper is to develop a conceptual sustainable packaging model that integrates the variables of technical design, supply chain systems and enviro...

High density (HD) pressboard is an essential element in power transformers combining good electrical insulation properties with effective mechanical characteristics that well suit design requirements of power transformers. In order to ensure a correctly functioning transformer, it is very important to characterize and to understand the mechanical p...

This book describes an approach to engineering education that integrates a comprehensive set of personal, interpersonal, and professional engineering skills with engineering disciplinary knowledge in order to prepare innovative and entrepreneurial engineers. The education of engineers is set in the context of engineering practice, that is, Conceivi...

The last three chapters have discussed answers to the second of the two questions central to the reform of engineering education: How can we do better at ensuring that students learn these skills? Integrated curriculum, design-implement experiences, integrated learning, and active and experiential learning are the main components of a reformed engi...

The purpose of engineering education is to provide the learning required by students to become successful engineers—technical expertise, social awareness, and a bias toward innovation. This combined set of knowledge, skills, and attitudes is essential to strengthening productivity, entrepreneurship, and excellence in an environment that is increasi...

The CDIO approach responds in an integrated and pragmatic way to the historical context in which engineering education finds itself and to the challenges that lie in the future. We call the collaboration of universities with at least one engineering program that has adopted a CDIO approach to engineering education the CDIO Initiative. The collabora...

In this chapter, we continue our discussion of the resolution of the second question central to the improvement of engineering education—How can we do better at ensuring that students learn these skills? In Chap. 4, we examined how the curriculum can be restructured and re-tasked in order to strengthen the links between the disciplines and weave th...

The objective of engineering education is to educate students who are “ready to engineer,” that is, broadly prepared with both pre-professional engineering skills and deep knowledge of the technical fundamentals. It is the task of engineering educators to continuously improve the quality of undergraduate engineering education in order to meet this...

Adapting and implementing a CDIO approach can be of great value to educational programs and the students they serve. However, that means change—an inherently challenging endeavor, especially at a university. Program leaders are more likely to succeed in this change process if faculty are equipped with an understanding of how to bring about change a...

The purpose of this work was to investigate to what extent it is possible to improve the thermoplastic properties of paper materials so that 3D-shapeable paper products can be manufactured. For that purpose, the addition of various chemical adjuvants, known to improve both tensile strength index and strain at break, was investigated. Adding polylac...

The strength properties of interfibre bonds play a vital role in the response of fibrous materials, such as paper and paperboard, under mechanical loading. To help tailor the properties of such materials by chemical or mechanical treatments of the fibre wall and fibre surfaces, improved understanding of the microscopic damage and failure mechanisms...

Cellulose-based components constitute the bulk of the current insulation for transformers. Cellulose is an organic polymer material which combines excellent electrical properties and good mechanical performance. As a polymeric material, cellulose is very sensitive to moisture and temperature. These factors can influence the electrical and mechanica...

The mechanical properties of interfibre joints are essential for the load carrying capacity of fibre network materials such as paper and board. Mechanical measurements of fibre–fibre crosses can been used to characterize the strength of these interfibre joints in order to obtain knowledge on how these hierarchical network materials behave at the mi...

We are presenting a coherent theoretical concept as well as empirical evidence suggesting that there is a high degree of molecular contact in fiber-fiber bonds, the surfaces might even be in full contact. Fundamental theoretical relations from contact mechanics governing the area in molecular contact between surfaces are reviewed and proposed for t...

The interfibre joint is one of the key elements in creating the strength of self-binding fibrous materials such as paper and board. In order evaluate the strength properties of interfibre joints using direct measurements, a greater understanding on how the mode of loading influences the results is desirable. The methods reported in the literature d...

The Scott bond test is the most commonly used test method for quantifying the delamination resistance of paper and board. The objective of this investigation was to validate the hypothesis that the Scott bond value would be dominated by the total energy under the force elongation curve in a z-directional tensile test. The investigation comprised th...

The crack tip region in notched structures generally exhibit damage evolution before ultimate failure occurs. In some materials, the damaged regions may reach considerable sizes prior to structural collapse. In this work, a cohesive crack model suitable for static fracture mechanics analysis of thin sheet materials exhibiting anisotropy, plasticity...

This graduate level textbook focuses on the mechanical properties and performance of products made of fiber-based materials such as paper and board. The book aims to help students develop effective skills for solving problems of product performance and engineering challenges in new product development. Therefore the material is organized with a pro...

This paper summarizes the dynamic analysis of the interaction of corrugated boxes in transport using a pressure‐mapping system. The dynamic contact forces on the contact area between boxes in both vertical and horizontal directions were measured, and the position of the instantaneous centre of force was traced, from which the pitch motion of boxes...

Experiments were made with a laboratory apparatus for forming paper sheets into double-curved structures. The purpose was to learn more about the design criteria for forming of paper materials into complex shapes. The influence of forming parameters such as moisture and temperature was studied, and the performance of some common pulps as raw materi...

Experiments were made with a laboratory apparatus for forming paper sheets into double‐curved structures. The purpose was to learn more about the design criteria for forming of paper materials into complex shapes. The influence of forming parameters such as moisture and temperature was studied, and the performance of some common pulps as raw materi...

Residual stresses are the stresses remaining in a material when all external forces are removed. Residual stresses in paper can influence the converting and end-use performance. There are wellestablished methods for determining residual stresses in paper, and some knowledge exists of how to control and tailor the residual stresses. However, there i...

During transportation from the manufacturer to the retailer packages are affected by vibrations, shocks, static and dynamic loads, as well as by changes in temperature and humidity. In order to improve the quality of the packaging to withstand stresses during transportation it is important to know the parameters that characterize the deformation st...

The Scott bond test method has been used extensively in the paper industry over the years as a means to assess the bond strength of paper. The method has been a subject of some controversy lately since it does not always correlate to the sensitivity of the material to fracture by delamination. To gain some further insight into which parameters gove...