Thesis (Ph. D.)--Virginia Polytechnic Institute, 1942. / Vita. Abstract. Includes bibliographical references (leaves 54-55). Also available via the Internet.

This master thesis has its main focus within embossing operations and how different factors influence the result. The work was performed at Stora Enso Research Centre in Karlstad, Sweden. Embossing is relatively complex operation to analyze since the paperboard can be exposed of both bending, shear and compression at the same time. The techniques used today for evaluating embossing on paperboard consist of experimental setups. These experimental techniques needed to be complemented in order to simplify the approach for embossing evaluations. The aim of this thesis was to develop a simulation material model, created with Finite Element Method by using Abaqus (2014), which capture the experimental behavior of embossed paperboard. The goals were to understand which material properties that are of high importance in embossing operations, and how sensitive the simulation material model is at small geometry changes of the embossing tool. A three dimensional finite element material model has been created in Abaqus (2014). The analysis was performed as dynamic quasi-static where an implicit solver was used. The simulation material model consisted of a continuum model, which describes the behavior of the plies, and an interface model implemented as cohesive elements, which describes the inelastic delamination between the plies. The continuum model was defined as an anisotropic linear elastic-plastic material model with isotropic linear hardening together with Hill´s yield criterion. The interface model was defined with an anisotropic elastic-plastic traction-separation law and an exponential damage evolution model. The purpose of the experimental tests was to capture the behavior of embossed paperboard and the goal was then to recreate the behavior in the simulation model. The results in this thesis focus on the relationship between the applied force and the displacement. An experimental and numerical study of out-of-plane compression has also been conducted, where the aim was to determine the out-of-plane elastic modulus, EZD. According to embossing results, the embossing results showed an exponential hardening behavior while the numerical results, unfortunately, showed a declining hardening behavior. Despite this, some understanding regarding which parameters that are of utmost importance have been achieved. The material parameters which had the highest influence on embossed paperboards seem to be the out-of-plane shear properties. This thesis also shows that the material model is sensitive of small changes of the tool geometry. The proportion of shear, bending and compression are strongly dependent on if the tool has sharp edges or if the edges are more rounded.

Crosslinked polymers or elastomers are examples of soft, synthetic material that can bend, crease, snap, wrinkle in response to external stimulus like pH, humidity, electric field or swelling. If a droplet of favorable solvent is placed on top of a thin, elastomer beam, it bends drastically to accommodate the excessive swelling stress. Keeping the solvent and its volume constant if we just increase the thickness of the beam, microscopic surface creases appear on the top surface. In this thesis, we experimentally characterize this transition between global bending to surface creasing. Closing of Venus flytrap leaves is a classic example of well known snap-through instability. A knowledge of the timescale of snapping is crucial in designing advanced functional materials. We perform the simplest experiment of poking an soft, elastomer arch at its apex till it snaps. Combining our experiments with analytical model we are able to predict the purely geometric nature of the snapping timescale. We also develop a simple scaling law that captures the dynamics of jumping toy poppers. / Master of Science

The introduction of creases into thin sheets has a dramatic effect on their global mechanical properties. This can be observed by manipulating a crumpled piece of paper which has been unfolded; it no longer deforms in the same way as the original sheet. Creases have typically been modelled as singular hinge lines, often accompanied by a torsional spring to provide some opening resistance; however, the appropriate stiffness of these springs is unclear. In reality, creases have a discrete geometry based on the method they were formed. This dissertation investigates the flexural behaviour of a creased thin metallic strip and the influence of the crease geometry. When a strip is bent perpendicular to the crease, putting the crease region in tension and the strip edges in compression, initially torsional deformations occur which ultimately coalesce into a central localised flattened region. An analytical model of this flexural behaviour is developed, which idealises the crease as an initially circular segment. Predictions show the bending resistance increases as the crease decreases in size. The model predictions are compared to finite element analysis and experimental results showing excellent agreement. When a strip is bent in the opposite direction, with the crease region in compression and the strip edges in tension, a bistable snap-through occurs. The deformed shape is characterised by a sharp vertex on the crease line. An analytical model is developed by generalising a Gauss mapping approach, and used to predict the deformed shape. These predictions match experimental results well. This dissertation provides an understanding of the mechanics of creased thin strips, where the crease is given a discrete geometry, and explores the nature of localisation. It also provides the foundation to explore the mechanics of thin sheets featuring a network of creases. This offers the opportunity to improve the efficiency of thin shell structures by using creasing to optimise the mechanics, leading to reduced material use, more sustainable construction, and fuel savings from lighter vehicles.

Crease-resistance is a very greatly desirable property in textile fibers. Of the natural fibers, wool exhibits this property to the greatest degree, followed by silk, cotton, and flax, which has a very low crease-resistance. The artificial cellulose fibers fall considerably below wool and silk in this respect. The improvement of the crease-resistance of rayon and other fibers has been sought in various after-treatment processes, in which substances are either deposited within the fiber, or react with it. There are numerous patents (22) for such methods of imparting crease-resistance. It would be highly desirable if the crease-resisting powers could be achieved "by a modification of the intrinsic properties of a fiber, that is, by producing a fiber which already is crease-resistant. The purpose of the work reported here was to attempt to produce a viscose rayon fiber with better crease-resisting properties, and to study the effect of a variation in the cellulose chain length distribution in the rayon upon this property. This work was done under a Fellowship of the Behr-Manning Corporation, Troy, New York. / Ph. D.

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (MScAgric (Horticulture))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Creasing, also known as albedo breakdown, is a preharvest disorder that affects the albedo of citrus fruit causing creases on the surface of the fruit. It is a recurrent problem in Navel and Valencia oranges and can cause individual orchard losses which often exceed 50%. Although the contributing factors are known, the physiological basis of creasing development is unresolved and the current control measures do not prevent creasing satisfactory. Hence, better control measures and further understanding of the physiology of creasing development is required. The objective of this two-year study was to determine if the position of fruit in a tree, light and carbohydrate manipulation techniques, and albedo mineral nutrients influence creasing development. Furthermore, the most effective application timing of gibberellic acid (GA3) with the least negative effect on fruit rind colour development and the effectiveness of cytokinins, other products and different root biostimulants to reduce creasing incidence were evaluated. The position of fruit in the tree and light influenced the development of creasing and the distribution of mineral nutrients in the albedo. Creasing incidence was higher on the south side than on the north side of the tree and fruit from the inside sub-sectors had a greater creasing incidence compared to fruit from the outside sub-sectors. The shady part of outside fruit was more creased compared to the sunny part of the fruit and covering fruit with brown paper bags increased creasing severity. The light manipulation techniques used on the leaves and fruit increased the nitrogen (N), phosphorus (P), potassium (K) and manganese (Mn) concentrations in the albedo and differences in the albedo mineral nutrients amongst the sub-sectors evaluated were observed, but creasing severity or creasing incidence was not significantly correlated with the albedo mineral concentrations at harvest. Albedo mineral concentrations earlier in the season may play a role in creasing development, as creasing severity was significantly correlated with copper (Cu), K, and Mn concentrations in the albedo during stage II of fruit development. Creasing incidence and albedo mineral concentrations were not affected by any of the carbohydrate manipulation techniques used in this study. The incidence and severity of creasing was significantly reduced, with a minor negative effect on fruit rind colour development, by the application of GA3, from mid November to mid January. Localised fruit application of CPPU [N-(2-chloro-4-pyridyl)-N-phenylurea], MaxCel (6- Benzyladenine) and CPPU in combination with calcium after physiological fruit drop reduced the incidence and severity of creasing, although creasing incidence was not significantly different from the control. The application of Messenger®, AVG (aminoethoxyvinylglycine) and different root biostimulants did not reduce creasing incidence. The results showed that cytokinins could reduce creasing incidence and justify further studies on application and uptake efficiency. The use of different root biostimulants are not recommended, but it is suggested that treatment effects may be more pronounced over a longer period. / AFRIKAANSE OPSOMMING: Kraakskil is ‘n vooroes abnormalitiet wat die albedo van sitrusvrugte affekteer, deur krake op die oppervlak van vrugte te veroorsaak. Dit is ‘n algemene probleem in Navel en Valencia lemoene en kan boordverliese van tot 50% of soms hoër veroorsaak. Alhoewel die bydraende faktore bekend is, is die fisiologiese basis van kraakskil ontwikkeling onopgelos en die beskikbare beheermaatreëls is nie bevredigend nie. Dus, beter beheermaatreëls en ‘n beter begrip van die fisiologie van kraakskil ontwikkeling is nodig. Die doel van die twee-jaar studie was om te bepaal of die posisie van vrugte in ‘n boom, lig en koolhidraat manipulasie tegnieke en minerale elemente in die albedo, kraakskil ontwikkeling beïnvloed. Die mees effektiewe toedieningstyd van gibberelliensuur (GA3) sonder ‘n negatiewe effek op vrugkleur is bepaal en die effektiwiteit van sitokiniene, ander produkte en verskillende wortel biostimulante om kraakskil voorkoms te verminder, is geëvalueer. Die posisie van vrugte in ‘n boom en lig het kraakskil ontwikkeling en die verspreiding van minerale element in die albedo beïnvloed. Kraakskil voorkoms was hoër aan die suidekant van die boom as aan die noordekant en vrugte in die binnekant van die boom het ‘n groter kraakskil voorkoms as vrugte in die buitekant van die boom gehad. Die skadukant van buitevrugte het meer kraakskil gehad as die sonkant en die toemaak van vrugte met ‘n bruin papiersak het die graad van kraaksil verhoog. Die lig manipulasie tegnieke wat op die blare en vrugte gebruik is, het die stikstof (N), fosfaat (P), kalium (K) en mangaan (Mn) konsentasies in die albedo verhoog en verskille in die albedo minerale elemente tussen sub-sektore is waargeneem, maar betekenisvolle korrelasies is nie tussen die graad en voorkoms van kraakskil en die albedo minerale element konsentrasies by oestyd waargeneem nie. Albedo minerale element konsentrasies vroeër in die seisoen mag ‘n rol speel by kraakskil ontwikkeling, omdat die graad van kraakskil betekenisvol gekorreleer was met albedo koper (Cu), K, en Mn konsentrasies tydens fase II van vrugontwikkeling. Kraakskil voorkoms en albedo minerale element konsentrasies is nie deur enige van die koolhidraat manipulasie tegnieke geaffekteer nie. Die voorkoms en graad van kraakskil is betekenisvol verlaag, met ‘n geringe negatiewe effek op vrugkleur, deur die toediening van GA3 vanaf mid November tot mid Januarie. Gelokaliseerde vrugtoedienings van CPPU [N-(2-chloro-4-piridiel)-N-phenielureum], MaxCel (6- Bensieladenien) en CPPU saam met kalsium na fisiologiese vrugval het die voorkoms en graad van kraakskil verlaag, alhoewel kraakskil voorkoms nie betekenisvol van die kontrole verskil het nie. Die toediening van Messenger®, AVG (amino etoksievinielglisien) en veskillende wortel biostimulante het nie kraakskil voorkoms verlaag nie. Die resultate het getoon dat sitokiniene kraakskil voorkoms kan verlaag en verdere studies op die toediening en opname effektiwiteit word aanbeveel. Die gebruik van verskillende wortel biostimulante word nie aanbeveel nie, maar die effek behoort meer sigbaar te wees na ‘n langer periode van behandeling.

This work resulted in a simulation platform and a validated numerical framework, which can precisely model the packaging material that are made of complex paperboard composite laminates and predict the material behaviour when it undergo es processing and converting procedures. Due to their specific advantages such as flexibility, hygiene, cost-effectiveness and environmental compatibility, paperboard composite materials are widely us ed for food and beverage packaging. The packaging materials are made of multi-layer sandwich laminates and mainly consists of several carton plies, a thin aluminium foil and several polyethylene layers. Compared to other conventional composite structures, such as carbon fibre composites, carton-based packages have an extremely thin composite structure with significantly softer material properties. To obtain a robust and well-formed commercial packaging, many manufacturing processes are usually carried out, for instance creasing, folding or bottom and gable sealing. In addition to the structural and architectural aspects, various technical requirements must b e met regarding functionality, rigidity and robustness of the packaging. During the converting procedures; especially at higher production speeds, unexpected operational flaws might b e observed often for material rupture and inter-layer delamination influencing the quality of a package performance. Furthermore, to examine the new paperboard material generations and operational developments, it is necessary to characterize and predict materials behaviour and packaging process if higher converting speeds, extended performance and efficiency are demanded. To satisfy the above-mentioned technical requirements, mathematical modelling and simulation methods are an appropriated way to formulate the paperboard material characteristics and analyse converting processes such as creasing and folding. A series of quasi-static and high-speed tensile tests were carried out to determine the mechanical properties of the highly anisotropic carton material. In addition to the classical tensile test, improved tests were also conducted specifically to measure the shear strength of the paperboard plies. Tests such as the Rigid Block Shear Test (RST) and the Double Notches Shear Test (DNST) were performed to obtain the shear stress curve and maximum shear strength across the paperboard thickness, respectively. Furthermore, the z-directional tensile test (ZDT) was also employed to identify the paperboard interfacial characteristics in terms of traction-separation curves. A mathematical model based on the finite element method (FEM) has been develop ed and implemented in the commercial ABAQUS software to simulate material behaviour under highly dynamic loads. The simulation model includes both constitutive elasticplastic formulation of packaging composite structure and a description of interlayer interaction and delamination between the composite plies as well. A formulation according to the Hill ´criteria has been used to formulate the anisotropic elastic-plastic behaviour of the material based on its rate-dependent characteristics. The interaction between the paperboard layers and the corresponding delamination during the creasing and folding processes have been implemented using an anisotropic traction separation model in respect to the relative sliding and opening of the adjacent interfaces. The most important simulation parameters have been comprehensively investigated and optimized regarding the calculation accuracy, simulation costs and efficiency. Subsequently, the obtained numerical results were successfully validated with available experimental data for practical static and dynamic creasing and folding processes.:1. Introduction 2. The State of the Art 2.1 Introduction 2.2 Paperboard and packaging composites manufacturing process 2.3 Paperboard converting process: creasing and folding 2.4 Analyzing of existing models for packaging materials and packaging procedures 2.5 Conclusions 3 Objective and Research Program 3.1 Objective 3.2 Research Program 4 Continuum Mechanics and Modeling of Packaging Process 4.1 Introduction 4.2 Continuum mechanics 4.2.1 Deformation gradient 4.2.2 Finite strain equations 4.2.3 Constitutive model and stress decomposition 4.2.4 Velocity gradient and rate of deformation 4.2.5 Yield criteria 4.2.6 Hardening law and plastic flow 0 4.3 Analytical model for paperboard material characterization 4.3.1 Constitutive equations 4.3.2 Elasticity 4.3.3 In-plane plasticity 4.3.4 Out-of-plane plasticity 4.4 Contact and interfacial formulation 4.4.1 Normal contact analysis 4.4.2 Tangential contact analysis 4.4.3 Interface model 4.5 Conclusions 5 Development of Experimental Methods for Paperboard Material Identification 5.1 Introduction 5.2 Quasi-static tensile test 5.3 Shear and interfacial experiments 5.3.1 Rigid block shear test (RST) 5.3.2 Double notched shear test (DNST) 5.3.3 Z-directional tensile test (ZDT) 5.4 Paperboard dynamic material characterizations 5.4.1 Dynamic test set-up and measurement 5.4.2 Dynamic material calibration and parameter identification 5.5 Conclusions 6 Paperboard Composites Converting Process Experiments and Finite Element Modeling 6.1 Introduction 6.2 Material and interfacial numerical modeling 6.3 Punching creasing 6.3.1 Punching creasing experiment 6.3.2 Punching creasing FE simulation 6.4 Dynamic creasing 6.4.1 Dynamic creasing experiments 6.4.2 Dynamic creasing simulation 6.5 Folding model 6.5.1 Folding experiment 6.5.2 Folding simulation 6.6 Conclusions 7 Results and Discussion 7.1 Introduction 7.2 FE results and validation 7.2.1 Quasi-static punching creasing process 7.2.2 High speed rotating dynamic creasing process 7.2.3 High speed folding process 7.3 Conclusions 8 Potential Analysis of Material and Process Optimization 8.1 Introduction 8.2 Material optimization 8.2.1 Material continuum characterization 8.2.2 Material interface characterization 8.2.3 Material shear characterization 8.3 Conclusion 9 Summary and Outlook