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  • 1
    Electronic Resource
    Electronic Resource
    A numerical-experimental method to characterize the non-linear mechanical behaviour of human skin (2003)
    Oxford, UK : Munksgaard International Publishers
    Skin research and technology 9 (2003), S. 0 
    Details
    ISSN: 1600-0846
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background/aims: Human skin is a complex tissue consisting of several distinct layers. Each layer consists of various components with a specific structure. To gain a better insight into the overall mechanical behaviour of the skin, we wish to study the mechanical properties of the different layers. A numerical-experimental method was developed to characterize the non-linear mechanical behaviour of human dermis.Methods: Suction measurements at varying pressures were performed on the volar forearm skin of 10 subjects aged 19–24 years old. Deformation of dermis and fat during suction was measured using ultrasound. The experiment was simulated by a finite element model exhibiting extended Mooney material behaviour to account for the non-linear stress–strain relationship. An identification method is used to compare the experimental and numerical results to identify the parameters of the material model.Results: C 10, dermis was found to be 9.4 ± 3.6 kPa and C11, dermis to be 82 ± 60 kPa. A first rough estimate of C10, fat was 0.02 kPa.Conclusions: The resulting finite element model demonstrated its ability to describe the response of the skin to suction at various pressures. In the future, this method can be used to characterize the mechanical behaviour of different skin layers using various aperture sizes and to characterize the skin behaviour under various loading conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1600-0846.2003.00019.x
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of hydration and experimental length scale on the mechanical response of human skin in vivo, using optical coherence tomography (2004)
    Oxford, UK : Munksgaard International Publishers
    Skin research and technology 10 (2004), S. 0 
    Details
    ISSN: 1600-0846
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Backgrounds/aims: Human skin is a complex tissue consisting of different layers. To gain better insight into the mechanical behaviour of different skin layers, the mechanical response was studied with experiments of various length scales. Also, the influence of (superficial) hydration on the mechanical response is studied. The work is based on the hypothesis that experiments with different length scales represent the mechanical behaviour of different skin layers. For suction, this means that a large aperture diameter reflects the behaviour of mainly dermis, whereas a very small diameter reflects the behaviour of only the top layer of the skin.Methods: Suction measurements at varying pressures and aperture sizes were performed on the volar forearm of 13 subjects aged 29–47 years. The deformation of the skin was visualized using ultrasound (US) (dermis) and optical coherence tomography (OCT) (epidermis and dermis). US measurements were performed on hydrated skin, OCT measurements on dry and hydrated skin. The experiment was simulated by a finite element model (FEM) exhibiting extended Mooney material behaviour. An identification method was used to compare the experimental and numerical results to identify the parameters of the material.Results: The material parameters C10 and C11 were calculated for four subjects: C10=29.6±21.1 kPa and C11=493±613 kPa for 6 mm aperture diameter, C10=11.5±8.7 kPa and C11=18.3±12.6 kPa for 2 mm aperture diameter and C10=10.8±9.5 kPa and C11=9.3±7.7 kPa for 1 mm aperture diameter. Skin hydration caused ambiguous effects on the mechanical response.Conclusions: US and OCT, combined with suction, using varying apertures sizes, proved to be a valuable tool to study the mechanical behaviour of different skin layers. With increasing experimental length scale, increasing values for the parameters of the material model were found. This indicates the need of a multi-layered material layer FEM, which can be used to identify mechanical behaviour of epidermis and dermis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0846.2004.00077.x
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  • 3
    Electronic Resource
    Electronic Resource
    Correlations between small aperture skin suction parameters: statistical analysis and mechanical model (2003)
    Oxford, UK : Munksgaard International Publishers
    Skin research and technology 9 (2003), S. 0 
    Details
    ISSN: 1600-0846
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background/aims: Skin suction experiments are widely used in order to evaluate the effects of skin treatments, both for cosmetic and for dermatological purposes. Classically, the elevation of the skin is measured at different discrete time instances after the pressure has been changed. Relations between the classical parameters – Uv, Ur, Ue and Uf – have been investigated and used in order to develop a new model for interpreting the mechanical properties of the skin.Methods: Within a group of 68 female subjects – aged between 37 and 68 – a Cutometer has been used in order to determine classical skin suction parameters on the female facial skin. Each skin suction measurement consists of three consecutive underpressure cycles. Within the resulting parameter set, a statistical analysis has been performed to investigate interparameter relations.Results: Strong interparameter correlations have been found within a set of 12 classical skin suction parameters. The set contains three independent groups of interrelated parameters. Based on this observation, a one-dimensional mechanical model – consisting of springs and dampers – is constructed. When two extra independent parameters are included in the model, the elevation versus time curves as recorded during three consecutive underpressure cycles can be fully described. The model reveals that typical skin suction data can be described in terms of a quick and a slow deformation process. The two characteristic time scales are 0.1 and 7 s approximately. The 0.1 s-value matches the response time of the device used. In reality, the quick deformation process in the skin may have a shorter time scale.Conclusions: In skin suction data, each underpressure cycle is usually characterized by four classical parameters – Uv, Ur, Ue and Uf. Within the 12 parameters of a three-cycle measurement, three independent groups of interrelated parameters have been found. These groups can be represented by the parameters Uv1, Ur1 and Uf1 of the first underpressure cycle.A model that is based on these three independent groups and two other independent parameters is proposed. The model provides an accurate description of the skin deformation as recorded during a measurement involving three underpressure cycles. The model is an improvement over classical interpretations of skin suction data where interrelated parameters are used. Moreover, the five-parameter model accounts for well-known mechanical characteristics of the skin such as preconditioning and visco-elastic behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1600-0846.2003.00016.x
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Discrete ductile fracture modelling for the metal blanking process (2000)
    Springer
    Computational mechanics 26 (2000), S. 104-114 
    Details
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Design and realisation of a metal blanking process in current industrial practice are mainly based on empirical knowledge. For more sophisticated applications, involving high accuracy geometry specifications, or non-standard materials and product shapes, this empirical approach often fails. This paper presents a set of interrelated numerical techniques resulting in a finite element model of the metal blanking process, focusing on the prediction of the shape of the cut edge of a blanked product. The large, localised deformations are handled by an Operator Split Arbitrary Lagrange Euler (OS-ALE) method supplemented by full remeshing. Transport of the state variables between subsequent meshes for the OS-ALE and remeshing methods is accomplished by the Discontinous Galerkin (DG) method and an interpolation procedure, respectively. Ductile fracture is incorporated using a discrete cracking approach, which is shown to generate mesh independent results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004660000158
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    A two-dimensional paving mesh generator for triangles with controllable aspect ratio and quadrilaterals with high quality (1998)
    Springer
    Engineering with computers 14 (1998), S. 248-259 
    Details
    ISSN: 1435-5663
    Keywords: Conversion ; High Aspect Ratio ; Mesh generation ; Paving ; Plastering ; Quadrilaterals ; Triangles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Certain classes of problems result in solution fields of which the characteristic length scales vary with the orientation. Often the orientation of these length scales is related to the orientation of the boundaries. Such solution fields can be captured by the finite element method, using a mesh that is refined in the direction of the short length scales and coarse in the other directions. These meshes contain elements with high aspect ratios in a predefined pattern. The mesh generator presented here can render triangles with high aspect ratios through a paving algorithm. The paving algorithm that is employed applies both triangles and quadrilaterals, combining the advantages of both to render a qualitatively good, oriented triangular mesh, with a concentration of elements in the direction where the internal length scales of the solution field are the shortest. The mesh generator produces triangles with one (almost) orthogonal corner. When low aspect ratio triangles are generated, these are well suited for conversion to quadrilateral elements. Test results indicate that quadrilateral meshes converted from the mesh generator introduced here have a considerably better quality than those converted from several other triangular mesh generators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01215978
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    Paper (German National Licenses)
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