Stefan Diebels's research while affiliated with Hochschule für Technik und Wirtschaft des Saarlandes and other places
What is this page?
This page lists the scientific contributions of an author, who either does not have a ResearchGate profile, or has not yet added these contributions to their profile.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
Publications (279)
![Experimental results from Neuhaus et al. [4] showing the damage of a...](publication/369822929/figure/fig2/AS:11431281142641997@1681178545084/Experimental-results-from-Neuhaus-et-al-4-showing-the-damage-of-a-cross-linked_Q320.jpg)
A viscoelastic material which is stretched and is then held at constant elongation, normally results in decreasing stresses till the equilibrium has been reached. With the decreasing stresses a crack propagation is not expected as the energy of the system is decreasing. However, an initial damage could lead to an increase in the mechanical load on...
Despite recent experimental and clinical progress in the treatment of tibial and fibular fractures, in clinical practice rates of delayed bone healing and non-union remain high. The aim of this study was to simulate and compare different mechanical conditions after lower leg fractures to assess the effects of postoperative motion, weight-bearing re...
In various applications, it is common to use thin beam-like structures, made of plastic or fibre-reinforced materials, as well as components such as cables. They are flexible, and the most common form of deformation is bending, but they can also be stretched or torqued. Due to their structural composition, a coupling between the different loading d...
Background:
The mechanical boundary conditions of the non-union and osteosynthetic construct are a key determinant of fracture healing after revision surgery. Aim of this study was to introduce a movement analysis and simulation workflow to determine the mechanical conditions during non-union healing in vivo.
Material and methods:
On an individu...
Cellular materials such as metal foams or auxetic metamaterials are interesting microheterogeneous materials used for lightweight construction and as energy absorbers. Their macroscopic behavior is related to their specific mesoscopic deformation by a strong structure‐property‐relationship. Digital image correlation and infrared thermography are tw...
Nonunion is a complication of long bone fractures that leads to disability, morbidity and high costs. Early detection is difficult and treatment through external stimulation and revision surgery is often a lengthy process. Therefore, alternative diagnostic and therapeutic options are currently being explored, including the use of external and inter...
This paper deals with the mechanical and thermal behavior of aluminium sheets with a rectangular perforation structure exhibiting an auxetic behaviour. The negative Poisson’s ratio is basically achieved by the rigid rotation mechanism of the squares between the perforations. In this work uniaxial quasistatic tensile tests are carried out to charact...
Parameter estimation for generalized Maxwell models for viscoelastic materials can become ill-posed when insufficient experimental data is available. In this article, we introduce a rheological model containing Maxwell elements, define the associated forward operator and the inverse problem in order to determine the number of Maxwell elements and t...
The limited quantity of raw materials leads to application-optimised materials, such as open-cell hybrid foams. A nanocrystalline nickel coating significantly enhances the crash absorber properties of aluminum and PU foams with only a small increase in weight. The coating is applied by an electrodeposition process. Due to mass transport limitations...
Non-union rate after tibial fractures remains high. Apart from largely uncontrollable biologic, injury, and patient-specific factors, the mechanical fracture environment is a key determinant of healing. Our aim was to establish a patient-specific simulation workflow to determine the mechanical fracture environment and allow for an estimation of its...
![SEM image of samples DP2 and DP3 after Beraha etching according to [62]...](publication/349425101/figure/fig5/AS:992789596753923@1613710893949/SEM-image-of-samples-DP2-and-DP3-after-Beraha-etching-according-to-62-in-SE-contrast-to_Q320.jpg)
Dual-phase steel shows a strong connection between its microstructure and its mechanical properties. This structure–property correlation is caused by the composition of the microstructure of a soft ferritic matrix with embedded hard martensite areas, leading to a simultaneous increase in strength and ductility. As a result, dual-phase steels are wi...
The sandwich cladding is a blast mitigation technique well described in the literature. One of the key parameters for its efficiency is a good knowledge on the crushable core placed inside the cladding. This paper focuses on galvanised polyurethane foams, a new family of hybrid materials which can fill the role of a crushable core. The galvanisatio...
Polyamide exhibits hygroscopic nature and can absorb up to 10% of moisture relative to its dry weight. The absorbed moisture increases the mobility of the molecular chains and causes a reduction in the glass transition temperature. Thus, depending on the moisture distribution, a polyamide component can show different stiffness and relaxation times....
Mathematical models describing the behavior of viscoelastic materials are often based on evolution equations that measure the change in stress depending on its material parameters such as stiffness, viscosity or relaxation time. In this article, we introduce a Maxwell-based rheological model, define the associated forward operator and the inverse p...
In this study, a model for the cross‐linking of ultra‐high viscous alginate hydrogels is provided. The model consists of four kinetic equations describing the process, including the local accumulation and the depletion of mobile alginate, cross‐linked alginate and cross‐linking cations. For an efficient simulation, finite difference schemes with pr...
Mechanical metamaterials are man‐made designer materials with unusual properties, which are derived from the micro‐structure rather than the base material. Thus, metamaterials are suitable for tailoring and structural optimisation to enhance certain properties. A widely known example for this class of materials are auxetics with a negative Poisson'...
Due to their complex structure cables exhibit an anisotropic behaviour and undergo large deformations in various applications. The large deformations are simulated using blended high order solid elements that can represent large deformations efficiently. To reduce the computational complexity the cross section consisting of many single wires and di...
In this study, we present a novel strategy to the method of finite elements (FEM) of linear elastic problems of very high resolution on graphic processing units (GPU). The approach exploits regularities in the system matrix that occur in regular hexahedral grids to achieve cache-friendly matrix-free FEM. The node-by-node method lies in the class of...
The thread-by-thread tear mending technique for canvas paintings represents an important field of research for the preservation of canvas paintings. This joining technology has been published and has become well established as a minimal invasive alternative for the treatment of local damage in the canvas, in contrast to the application of patches o...
The computer-aided design of individual parts and the desire for weight reduction and material savings require further development of new hybrid materials. Ni/PU hybrid foams as a new hybrid material offer great potential for the production of components that are lightweight and yet can absorb large amounts of energy. The development of this struct...
Hybrid foams are an evolution of classic metal foams. They consist of an open-cell foam template coated with a second material. Thereby, the coating material dominates the material behaviour of the hybrid foams. Ni/PU hybrid foams are a suitable example of hybrid foams. An inexpensive polyurethane (PU) foam is coated with nanocrystalline nickel (Ni...
Metal foams exhibit excellent characteristics suitable for a variety of light weight construction applications, based on outstanding specific mechanical properties and the ability to provide a nearly constant force during energy absorption. All components are subjected to multiaxial stress states during the application. In order to ensure a safe de...
The paper introduces the technique of thread-by-thread tear mending in the conservation of canvas paintings and is dedicated to the investigation of difficulties in the reproducibility of bonding qualities. An insight is given into the basics of the bonding technique as well as the requirements on the adhesives. Based on initial test series, the ca...
Various studies have reported the changes in the mechanical properties and the modification in morphology of polyamide due to the absorption of water. However, the relation between the local water content and the alteration in the properties has not been consolidated in a coupled model yet. In the current work, a simulation model is proposed that c...
Cellular materials, such as open cell metal foams, consist of a complex microstructure effecting the global material behaviour. The characterisation of the macroscopic material behaviour is complex and requires a multitude of different experiments. Material models that treat the metal foam as a continuum can describe the observed behaviour from the...
In stress relaxation experiments the investigated polyurethane exhibits an unexpected, but repeatable failure during the relaxation period. Images, taken by a camera and a high speed camera, displayed crack initiation several minutes before rupture occurred. The crack growth rate then accelerates and leads to failure rapidly. The present investigat...
Closed-cell polyvinylchloride (PVC) foams are widely used as core for sandwich composites for applications, in which multiaxial loads are involved. In the present work a wide range of uniaxial (tension, compression and torsion) and multiaxial experiments (both simultaneous tension-torsion and compression-torsion) were conducted on a high performanc...
Tailored design of application-optimised foam components requires the prediction of the mechanical properties by a numerical simulation model. Simulations that are able to account for microstructural changes are very time-consuming and not efficient. Hence, scale-bridging must be applied between the application-specific macroscale and the microscal...
Open cell metal foams are interesting lightweight materials, which are used in a variety of applications. Effected by the complex microstructure of open cell metal foams the macroscopic material behaviour cannot be described with a von Mises yield criterion. In comparison to bulk metals, open cell metal foams collapse under hydrostatic compression...
Digital image correlation (DIC) is well known as a contact‐less, full‐field strain and displacement measuring method. The use of the method is widely spread in experimental mechanics. Nevertheless, there are error sources such as light settings, speckle pattern and noisy images, which strongly affect measurement quality, but often stays uninvestiga...
Porous materials such as bones, sponges or cork are used in nature due to their light weight. Metal foams with stochastically distributed pores are such a porous bionic material based on nature. Their low weight and mechanical properties make them perfect for use in aerospace, automotive and building construction industry. To improve the mechanical...
The interfragmentary movement (IFM) is a key determinant for the fracture healing process. Different simulation models allow the prediction of the IFM in the fracture gap based on an estimated ground force. For this purpose, a workflow capable for implementation into the clinical routine workup was developed as a proof of concept based on individua...
The mechanical properties of thermomechanical rolled low alloyed (TM) steels highly depend on their microstructure, which is formed during the production processes of the metal plate. Additionally, an elastic‐plastic anisotropy is encountered in these materials due to the texture of the ferritic grains. Hence, the material exhibits different stress...
Metal foams are a very interesting class of cellular materials which, due to their structure, can be used both for lightweight construction and for the absorption of kinetic energy. They have a microheterogeneous structure, which makes it difficult to simulate these materials efficiently. Although microstructure models are very precise in terms of...
The increasing number of vehicle components and the advancing lightweight construction in manufacturing processes increasingly require a more flexible design of the exhaust tube geometry. The use of process supplementary simulations is necessary, in order to meet these increasing requirements in the future.
The aim of this study is the development...
This paper deals with the formulation and numerical implementation of a coupled continuum model for deformation, diffusion and damage in viscoelastic materials like polymer adhesives to analyze the influence of aging behavior on damage phenomena. The formulation is based on a continuum mechanical model. In order to couple diffusive moisture transpo...
In recent years, the wall thickness of exhaust tubes has been reduced due to lightweight construction, which makes the error-free formability significantly more difficult. Since at the same time the outer diameter has risen, the final assembly has become more complex due to a lack of space, because the exhaust tube is installed as last component in...
Uniaxial and biaxial testing of a three‐dimensional (3D) printed photopolymer (TangoBlackPlus) is performed. The nonlinear material response is studied using specially designed uniaxial and biaxial coupons. Experimental results show a quasi‐isotropic and hyperelastic behavior for longitudinal and transverse directions parallel to the 3D printer bui...
Hammer blows cause serious, often fatal injuries, especially when massive blunt violence is targeted at the head region. The evaluation of the injury potential depends not only on the body region hit, but also on the characteristics of the hammer as a weapon and on the physical characteristics of the attacker.
This study aimed at elucidating the de...
Cellular materials such as foams, honeycombs, or auxetic structures are an interesting type of structural materials for lightweight constructions or dynamic energy absorbers. These microheterogeneous materials consist of a hierarchical structure. Foams can be separated into a macro scale, meso scale, and micro scale dealing with the entire specimen...
Closed-cell polyvinylchlorid foams are among the most used core materials for sandwich composites. Therefore, a deep knowledge of their multiaxial behaviour is fundamental. More precisely, a literature review proves the lack of investigations concerning combined tensile-torsional loadings. In the present work simple tests, namely tension, compressi...
Open-cell metal/polymer hybrid foams are biomimetic open-porous composites, consisting of a polymeric foam electrochemically coated with a metallic layer. Due to their specific pore structure, they can be used in lightweight applications or as crash absorbers. The nanocrystalline coating leads to a strengthening effect and largely improved energy a...
The theoretical results presented in the previous chapters are based on experimental investigations. Therefore, in this chapter, the experimental characterisation of the short fibre-reinforced composite is presented. The performed experiments increase in complexity, starting from uniaxial tensile tests at different strain rates up to multiaxial tes...
In this study, several mappings for material parameters based on computed tomography image data are tested with respect to their influence on the result of personalized finite element simulations (FEM). Therefore, a standard workflow was implemented including (1) segmentation of routinely acquired clinical tomogram data, (2) definition of several m...
The complex microstructure of open cell metal foams results in beneficial global material properties like a good weight to stiffness ratio, which makes this special group of cellular materials interesting for several applications. Open cell metal foams are suitable for lightweight applications as well as for energy absorbing systems. The dependency...
Based on an increasing demand of energy and raw materials, resources should be used more efficiently. Therefore, multifunctional materials and lighter constructions, which can endure higher payloads, are needed. Cellular materials like metal foams are bionic, multifunctional materials, which can be optimised by a coating of the foam structure. Due...
This paper deals with the auxetic deformation behavior of periodically perforated aluminum sheets and their application for lightweight design. If commercially available metal sheets are provided with perforations, this can significantly change the mechanical properties of the sheets. For example, with certain perforation patterns, it is possible t...
Chapter B.6 discussed the extension of visco‐elastic adhesive models to account for different spatially varying influence factors, for example the local concentration of water in the adhesive. While this kind of extension offers the potential to improve the modelling, it seems to imply a large increase of effort in the simulation of the behaviour o...
In this chapter a detailed model for adhesive joints is presented. The model is based on a three‐dimensional continuum mechanical framework. The visco elastic properties are coupled to further effects which are required to describe the evolving mechanical properties during aging. Based on the experimental investigations on polyurethane and epoxy jo...
The basic principles of continuum mechanics are presented. The three essential aspects of kinematics, balance equations and constitutive modelling are introduced. This framework allows for the modelling of thermomechanically coupled problems. Modern multi‐physics problems require further effects to be included. Therefore, the continuum mechanical c...
Open-cell metal foams are biomimetic open-porous materials mimicking the construction elements of bones. Based on their special porous microstructure, they are used as lightweight construction elements and for crash energy absorbers. Ni/Al hybrid foams are aluminium (Al) foams electrochemically coated with nanocrystalline nickel (Ni) leading to enh...
In this study, the concept of applied clinical mechanics is used to present first steps in the direction of personalized orthopedic trauma surgery. As example process, a complex distal tibia fracture treated with an implant is chosen. Based on an automated workflow, routinely acquired tomographic data is segmented, assigned with material parameters...
Metal foams are cellular materials, offering a strong structure-property relationship. Their global properties are strongly connected to the local micromechanical properties of the struts and to the microstructure of the foams. The mechanical properties of individual struts differ widely from the bulk matrix material as a result of differences in s...
For studying the interaction of displacements, stresses, and acting forces for elastic and viscoelastic materials, it is of utmost importance to have a decent mathematical model available. Usually such a model consists of a coupled set of nonlinear differential equations together with appropriate boundary conditions. However, since the different ma...
This chapter deals with the deformation behavior of flexible slender structures such as cables or hoses. In addition to their main functions, conducting electric current or other media, their mechanical properties gain importance, since the number of applications where cables are loaded mechanically increases. The first section of this chapter deal...
Metal foams are an interesting class of biomimetic materials that are used as lightweight construction elements or as energy absorbers. Foams are micro heterogeneous materials, and the global mechanical properties of a component are strongly affected by the local micro mechanical properties due to a complex structure-property relationship. The pres...
In this study, a workflow is presented for a personalized simulation of a bone–implant–system of a fractured tibia during a step forward. The workflow is based on routinely acquired tomographic data, segmentation, material assignment, mesh generation, setup of realistic boundary conditions and a finite element simulation (FEM). In the absence of pa...
This contribution deals with the experimental investigation of cables showing inelastic behavior under bending deformation. A new experimental device, which enables the direct measurement of the quantities entering the constitutive law for bending, i.e. the bending moment and bending curvature, is introduced. Results from advanced cyclic experiment...
In general, mechanical properties of Al-Si alloys strongly depend on the morphology and arrangement of microconstituents, such as primary aluminium dendrites, silicon particles, etc. Therefore, a detailed characterization of morphological and mechanical properties of the alloys is necessary to better understand the relations between the underlined...
Composite materials are of great interest for industrial applications because of their outstanding properties. Each composite material has its own characteristics due to the large number of possible combinations of matrix and filler. As a result of their compounding, composites usually show a complex material behavior. This work is focused on the e...
The field of nanocrystalline coated metal foams and nano hybrid foams respectively is a very new research area, in which various studies still have to be performed to earn a better understanding of the highly innovative materials. In the case of nano-coated hybrid metal foams, nanoindentation is the only method to determine the exact micromechanica...
In this study, a new approach to model the system of dimples on the fracture surface of Al-Si alloys using the weighted Voronoi tessellation is proposed. The tessellation model is applied to metallographic images of the eutectic phase to simulate a fracture surface appearance (as projected on a fractograph) that would potentially exhibit this struc...
Metal foams are bio-inspired microheterogeneous materials, which exhibit a strong structure-property relationship. Their global mechanical properties depend strongly on the local micromechanical properties of the struts and on the pore geometry of the foams. A solid micromechanical and macromechanical understanding of the yield behaviour of the foa...
This contribution presents a possibility how to characterize composite materials with respect to experimental testing. Furthermore a modeling approach is presented based on the experimental results. Composite materials, like short fiber reinforced polymers, are of great interest because of their good properties for industrial applications. In this...
Modern dual-phase (DP) steels are widely used in industry due to their favorable material behavior based on the complex microstructure. In the presented work, a microstructure based FEM model for the elasto-plastic deformation of DP steels is developed in order to accomplish a deeper understanding of the structure-property correlation. The underlyi...
Open cell aluminum metal foams are a new kind of material that are used in composite structures to reduce their weight, to increase their sound or energy absorption capability or to decrease their thermal conductivity. The design and analysis of such structures requires a macroscopic constitutive model of the foam that has to be determined by vario...
This contribution presents the characterisation of an incompressible carbon black-filled elastomer as one characteristical example for highly filled rubber material. The material model is developed with respect to uniaxial tension data. The experiments show that a strongly pronounced non-linear viscoelastic material behavior is present and the most...
Refractory materials such as magnesium oxide carbon (MgO-C) composites are used in the steel-making industry for furnaces, ladles or oxygen converters. A new class of composites are cellular MgO-C materials, consisting of carbon foams filled with magnesium oxide and inclusions of gas filled pores. Cellular MgO-C composites have the advantage of sig...
This contribution discusses an experimental possibility to characterise a cellular rubber in terms of the influence of multiaxiality, rate dependency under environmental temperature and its behaviour under hydrostatic pressure. In this context, a mixed open and closed cell rubber based on an ethylene propylene diene monomer is investigated exemplar...
Metal foams are bio-inspired microheterogeneous materials with great potential for application in lightweight construction or as kinetic energy absorbers. Based on their complex microstructure, the global properties depend strongly on the local properties of the microstructure. According to the compressible behaviour of metal foams, there is a loca...
Flexible, slender structures like cables, hoses or wires can be described by the geometrically exact Cosserat rod theory. Due to their complex multilayer structure, consisting of various materials, viscoplastic behavior has to be expected for cables under load. Classical experiments like uniaxial tension, torsion or three-point bending already show...
The relationship between microstructure and mechanical behavior of the eutectic phase in hypoeutectic Al-Si alloys is analyzed empirically using two experimental and thirteen synthetic microstructures. For all microstructures, a morphological analysis is combined with mechanical stress-strain simulations performed via finite element method (FEM). T...