Experimentelle Ermittlung von Werkstoffkenngrößen für innovative Leichtbauprodukte – Bauschinger‐Kenngrößen für 54SiCr6 auf Basis von Zug‐/Druckversuchen

Simulation of multiple plastic bending deformations processes with loadings vice versa needs suitable parameters. For high‐strength spring steel there are not enough investigations available. Investigation and comparison of appropriate parameters for 54SiCr6 will be shown. On the one hand the results of tensile/pressure trials at 54SiCr6 shows that Bauschinger‐Effect is existing. Dependence of tangent modulus and plastic reverse deformation to degree of plastic deformation are obvious. Tangent modulus is decreasing according to increasing plastic deformation – plastic reverse deformation increases according to increasing plastic deformation. Investigated parameters probably depend to degree of plastic deformation and do presumable not accord to deformation history.     

Einige Gesichtspunkte für die Auswahl von Stählen in der chemischen Höchstdrucktechnik

Some Aspects of Selecting Materials in the Chemical High Pressure Technology . Steels for chemical industry in the pressure range between 2000 and 3000 bar must have high yield strengths in order to be able to bear the static internal pressure. Even with high yield strengths the wall thickness is so high that steels must be selected which can be thoroughly and evenly quenched and tempered. They should be insensitive to tempering embrittlement. For components stressed by static internal pressure the safety against bursting and the bursting behaviour play a major rǒle. In addition to that, under pulsating pressures, the fatigue characteristics of a component are of importance. Steels with the high fatigue strengths necessary in high pressure application are notch sensitive. It is shown which measures are to be taken from the metallurgical side and in fabrication to increase their fatigue strength. Results of fatigue tests on high pressure tubes with different surface treatment are given. The fatigue strength can be improved by improving tube manufacturing, mechanically or electrochemically smoothening the inner tube surface, nitriding or autofrettage. For special purposes it is sometimes necessary to use steels whose strength is too low for high pressure applications. One must then apply a strength calculation conceding partial plastic deformation. This is illustrated for an age hardening austentitic steel.     

Verifizierung numerischer Verfahren zur Modellierung abrasiver Verschleißprozesse durch Berechnung von Scratchtests

Verification of numerical methods for modeling abrasive wear processes by calculating scratchtests Abrasion is a fundamental wear mechanism. It occurs whenever surfaces are loaded tribologically by hard particles or roughness peaks. The scratch test shows the behavior of a surface during abrasive stress. For that purpose a diamond tip (indenter) moves onto the material with either constant or progressive normal force. At first the material will be deformed elastically; with increasing force plastic deformation occurs till crack‐ and chip‐forming, depending on the ductility of the material. Using elastic and plastic indentation depth, friction, acoustic emission through cracks and the three‐dimensional analysis of the scratch, wear resistance to scratch‐stress can be characterized. The simulation of scratch tests is useful to verify material models comparing the relative easily and quickly accomplishable tests with the simulation results. Based on this verification new or existing material approaches can be adapted even better to applications. The article describes problems and solutions during implementation of the simulation of the scratch test for the steel C45 (normalized). The comparison with experimental results shows that this approach is successful. In the future a closed material model for this type of stress will be developed.     

Vakuumkomponenten für UHV und XHV aus Aluminium

Vacuum components of aluminum for UHV and XHV — weldability and outgassing behavior It has been shown that present‐day aluminum alloys possess sufficient stability to produce aluminum CF flanges for multiple tightening cycles. In order to preserve the mechanical strength it is vitally important that the critical limiting temperature of the materials is not exceeded both during the production process and later in the application. Reproducible welding parameters guarantee vacuum tight welding seams with neat root formation. It could be verified experimentally that critical temperatures in the knife edge area will not be exceeded in case of design according to material properties and special welding parameters. Comparative measurements of identically designed vacuum chambers of stainless steel and aluminum proved that UVH conditions can be achieved much faster and with less energy input (lower bakeout temperature) with aluminum than with stainless steel.     

Versagenskriterien für Kunststoffe. Teil II: Experimentelle Ergebnisse

Failure Criteria for Polymers, Part II: Experimental Results . Using the fracture criteria, which have been analytically derived in the first part of this paper, experimental results from literature and from own experiments are compared with calculated fracture loci for thermoplastic materials, thermosets, and glassfibre-reinforced plastics. It can be shown that the change of dimension of a plastic specimen under load is simulating a higher compressive strength in comparison to the tensile strength (m > 1). Different methods are indicated for evaluating biaxial loading tests. A comparison between the results theoretically and experimentally found marks the parabolic fracture criterion to be suitable. Resins reinforced with chopped strand mats satisfy the maximum stress theory. The fracture behavior of orthotropic materials is accurately described by the fracture criterion of Tsai and Wu and Goldenblat and Kopnov. If normal stresses act parallel to the axis of orthotropy, the fracture behavior of orthogonal isotropic materials can be calculated acc. to the maximum stress theory.     

Analysis of steel‐reinforced masonry walls regarding maximum shear loads / Traglastberechnung von vertikal bewehrten Mauerwerksscheiben

Loadings on masonry for the earthquake case pose particular challenges for the material. In order to improve the load‐bearing and deformation behaviour, masonry building elements can be strengthened with reinforcement. This article presents an analytical model for the calculation of the load‐bearing capacity of vertically reinforced masonry panels. The masonry is modelled as a homogeneous and anisotropic material and failure conditions are based on the plastic theory. Using uniaxially loaded stress fields and considering the structural constraints, a lower load‐bearing threshold can be given. In order to verify the model, three shear tests on reinforced sand‐lime block masonry were recalculated regarding their load‐bearing capacity. The test panels each contained vertical steel reinforcement in the blocks. The blocks were laid in thin bed mortar.     

Anstrengungshypothese für Metallklebverbindungen

Macroscopic Failure Criterion for Metal-to-Metal Bonds In order to judge the load limit of metal-to-metal bonds, one needs, on one hand, characteristic values of strength which can obtained by experimentation with a defined state of stress, and on the other hand, failure criteria which determine stressability caused by any multidimensional state of stress in comparison to the strength characteristics obtained. Starting from the theory of the plastic potential for polymers, a failure criterion is formulated for metal-to-metal bonds. It is assumed that the adhesive-bonded joint is an homogeneous isotropic body. The evalution of some of the experimental results given in the literature on the subject show that the failure criterion for quasistatic loaded metal-to-metal bonds can be applied.     

Ventilwerkstoffe für Verbrennungsmotoren

Valve Materials for Combustion Engines An overview is being given on production numbers, requirements and properties of valve materials. Their development from the beginning till today's state of the art is reviewed with a focus on Chromium-Manganese-Nitrogen-alloys. Valve materials are grouped by the criteria of density – heavy, lightweight – and alloying elements. The multiple stresses of the material in the valve are being met with a few standardised grades and specific ways of manufacture. The path of the material from bar stock to the finished valve is being followed. Engine development in the past decades increased the load on the valves which could be met by continuously developing their structural strength. Also the strength of all valve materials could be raised to nominal strength above 1100 Mpa by applying specific methods. Higher strength at the surface is being effectuated by work hardening effects. The technology to increase reliability of hollow valves and new aspects of valve seat facing including residual stress is explicitly discussed. General aspects of alloy utilisation is followed by a discussion of lightweight valve materials as Titanium alloys, intermetallic Titaniumaluminide alloys and ceramic materials, spec. Silicon Nitride, which all have a potential as forthcoming valve materials capable of reducing fuel consumption of the engines.     

Local limit loads in components with competing failure locations

The plastic limit load is an important feature of the S‐N curve. The classical way of plastic limit load calculation using elastic‐ideal plastic material behaviour is restricted to one location of the component. Complex components normally have several fatigue critical locations, for all of them the local plastic limit loads has to be determined. By the classical way the plastic limit load can be evaluated only for one of them. A new method is presented. The local plastic notch factor K_p and the corresponding plastic limit loads are calculated applying Neuber's rule to FE calculations with plastic hardening material. The new method is validated on the basis of six different notched specimens. The need and capability is exemplarily shown on a specimen with two competing failure locations.     

Statistischer Größeneinfluß unter mehrachsiger Wechselbelastung

Statistical Size Effect Under Alternating Load The results of 41 series of tests with smooth cylindrical and notched specimens, subjected to uni- and multiaxial alternating loads (tensioncompression, torsion, rotating bending and combined torsion and bending), are compared with theoretically predicted data. The prediction are based on the ?Weakest-Link-Concept”?. Multiaxial stresses are included either by means of suitable strength criteria, or by a fracturemechanical consideration of a crack in a multidimensional stress field. For the evaluation of the experimental data the 2-parametric Weibull's equation was used. The experimental and theoretical results may deviate by less than 20%, when the ratio between the strength at cyclic torsion and cyclic bending ist taken into account in the function of survival probability [eqns. (2), (7)].     

Auswahl von Materialgesetzen und Parameteridentifikation für nichtlinear-elastische Werkstoffe

Selection of Material Laws and Identification of Material Parameters for Nonlinear Elastic Materials Elastomer components are used for a wide range of applications (e.g. seals, load introduction and damping elements, coatings). Their importance for the proper function of complete subassemblies has continuously increased over the last years. Despite the comparatively low cost of elastomer parts the design and testing of these components requires a high standard of expertise and thorough understanding. Modern analysis and appropriate software tools (e.g. finite-element codes) are utilized by manufacturers and customers (OEMs) to simulate the behavior of elastomer components under operational conditions. Realistic geometries and boundary conditions can be investigated at acceptable expenses. The quality of the results obtained depends substantially on an accurate model for the complicated material behavior. This article provides an insight into development and application of material laws which describe the hyperelastic and viscoelastic behavior of elastomer materials. Suitable experimental and numerical procedures are presented to identify the material parameters. The verified material models are input to structural analyses, dimensioning and assessment of strength and long-term behavior for elastomer components.     

Stabilität von Druckeigenspannungen unter zyklischer Beanspruchung für autofrettierte Bauteile aus Aluminium

Autofrettage provides the possibility for increasing the fatigue strength of internal pressurized components. This technique introduces compressive residual stresses, applying a single pressure overload prior to the service load. Whereas a lot of investigations for steel materials have been done so far, this report refers to the potential of the autofrettage process for the aluminum wrought alloy EN AW‐6082‐T5. In order for residual stresses to ensure a reliable increase of the stress amplitude, they must not be relaxed. A significant increase in lifetime at a load amplitude of Δp = 500 bar is shown for T‐shaped bore intersection specimens that are autofrettaged at a pressure of 1500 bar. The introduced residual stresses did not relax after 2.5×10⁶ number of cycles. Only for a load with a maximum equivalent stress above the yield strength the components initial compressive residual stress distribution is changed and even partially transferred to the tensile section. Therefore, using autofrettage is appropriate to increase the fatigue strength of aluminum components.     

Reinforced bending load‐stressed masonry – Suggestions for future designs / Bewehrtes biegedruckbeanspruchtes Mauerwerk – Vorschläge für zukünftige Bemessungen

European standardization bodies are currently working on the amendment to EN 1996‐1‐1, which will also affect the evaluation of reinforced masonry in Germany. For that reason, discussion suggestions are being made here for revisions to lay the groundwork for building materials evaluations and especially, evaluations of bending load‐stressed masonry walls or beams at their serviceability limit state (SLS) for load‐bearing capacities. Information already presented in E DIN 1053‐3:2008‐03 [N3] is being incorporated as well. Characteristic values for the compressive strength of the masonry parallel to the bed joints f_k,∥ are essential for the design of reinforced masonry, although they are currently not included in national application documents for Germany. For the time being, they can be mathematically calculated using conversion factors for the characteristic compressive strength values vertical to the bed joints f_k or by using the declared axial compressive strengths of the masonry units. The ultimate strains for masonry in general should be set consistently at ?_mu = ∣–0.002∣ as several masonry types do not exhibit higher compressive strain values. The use of steel strains higher than ?_su = 0.005 does not change any measurement results. Varying stress‐strain curves of the constitutive equations on masonry under compressive strain (parabolic, parabolic‐rectangular, tension block) lead to differing values of recordable bending moments despite having the same mechanical reinforcement percentage at higher normal forces. Therefore, clear guidelines should be made for the type of applicable constitutive equation for masonry walls under compressive strain. With the introduction of a tension block, the number values of the reduction factors λ for the compression zone height x, which is dependent on limit strains, and where applicable, reduced compressive strength, need to be determined, as with reinforced concrete construction. A modification of the bending moment based on the second order theory according to [N4] is presented for the calculation of reinforced masonry walls in danger of buckling. The use of reduction factors for the load capacity of the masonry cross section, such as for unreinforced masonry, does not appear to be appropriate as buckling safety evidence because here, the design task is the determination of a required reinforcement cross section.     

Schichtentwicklung für die schmiermittelfreie Umformung von hochfesten Aluminiumwerkstoffen

Development and evaluation of coatings for lubricant free forming of high strength aluminium Many applications in light weight construction require massive formed high strength aluminium parts. For economical and ecological reasons the use of lubricants for massive forming has to be avoided. Both, lubricant free forming and processing of high strength materials are big challenges that can be realized by using coated tools with functional surfaces that show high wear resistance, low friction and low adhesion to aluminium [1–7]. For goal‐oriented surface engineering different coating technologies, such as Physical Vapour Deposition (PVD) and Chemical Vapour Deposition (CVD) have been used for the preparation of specimens. The coating properties are evaluated by mechanical tests and numeric simulation to investigate the massive forming processes and the coating‐substrate‐behaviour. On the base of TiCN‐, TiC‐TiN‐ and DLC‐coatings on steel it is shown how relevant coating properties like Young’s Modulus, crack behaviour and hardness can be analyzed with regard to small coating thicknesses. In order to scale up the results to industrial conditions, finally the simulation is correlated to real deforming.     

Partikel- und Faserverbundwerkstoffe für Flüssigkeitsfreie Lager

Composite materials including particles and fibers as oil-less bearing materials Oil-less bearing can be fabricated by polymers and metals including solid lubricants (up to 10 w %) like PTFE, MoS₂ or graphite. If it is necessary by application to incorporate a greater content of solid lubricants, the mechanical properties of the composite materials are too weak. The mechanical properties of bearing material increase, when high tensile strength fibers are incorporated. In the case of graphite fiberreinforced polymers wear rate as well as coefficient of friction decrease, while the ultimate flexural strength increase rapidly. In the case of metallic matrices containing graphite fibers or steel wires the ultimate strength increases (above all the combination white metal/steel wire) as well as the wear rate decreases.     

Introduction of Planar High Pressure Torsion (P‐HPT) for Fabrication of Nanostructured Sheets

A new severe plastic deformation process based on conventional high pressure torsion is introduced. The process, called planar high pressure torsion (P‐HPT), is capable of inducing large shear strains into materials with planar geometries, such as sheets or strips and can basically be implemented on every standard HPT machine. The principles of this technique will be presented and accompanied by a case‐study, where P‐HPT will be applied on a sheet of pure copper with dimensions of 220 × 110 mm² and a thickness of 0.75 mm. For comparison, the material is deformed by conventional high pressure torsion using standard specimens with a diameter of 8 mm as well. It will be shown that the mechanical properties and microstructure obtained by P‐HPT correspond well to conventional high pressure torsion results.

     

Randschichteigenspannungen durch mechanisches Schleifen bei hochfesten Federstählen

Oil tempered steel, like the high strength spring steel 54SiCr6 (1.7102), is mainly used for helical springs. To enlarge the contact area between spring and adjacent parts, the spring tail is often flat‐grinded. Due to wire‐drawing process residual stress is already existing before spring manufacturing. The spring manufacturing process contains several sequenced steps like winding, even grinding and shot peening. All of these steps cause additional or influence the existing residual stress in wire. The knowledge of these mechanisms and the level of residual stress is mandatory for design of application and its operation. Grinding processes in general has major influence to the residual stress level. In fact the choice of grinding parameter is essential for the stress height. In general: thermal effects while grinding cause basically tensile stress, mechanical effects cause basically pressure stress. Presented investigation shows the qualitative influence of several grinding parameters like infeed, conventional or synchronized grinding operation mode and the optional usage of cooling lubricant. The superposition of grinding‐based residual stress with different residual stress depends not only on the stress‐height but also on the characteristic. Therefore universally statements are not available.     

Beschichtungen für Life Science

Coatings for Life Science Thin film technologies being well known from semiconductor industry and corresponding technologies for microstructures are successfully used in Life Science (medical technology, pharmaceutical research or biology). These technologies are the base of the complex and miniaturized life science products. Life Science is a strongly growing part of microsystems technology enabling innovations like the cochlear implant replacing the human ear or new products like the retina implant, the latter being shortly before market entrance. Since 1960 the use of plastic material in this field grew rapidly and still today it is a growing market for plastic material manufacturers. The reasons are cheap production and easy way to sterilize plastic material disposables.Unfortunately in many cases plastic materials do not possess the desired surface properties. But an additional (functional) coating may lead to the necessary properties. Low pressure vacuum technology as a sub group of vacuum coating technology is well suited for this surface modification. Normally process temperatures are only between 20 °C – 60 °C. Ceramic and metal based products in Life Science can be modified, too. There is a wide range of coating applications e.g. diamond like coatings on stents leading to decreased thrombus formation. In this overview basics of vacuum coating technology and plasma technology are described and examplarily some aspects and applications in Life Science are shown.     

Ansätze für ein Zähigkeitskriterium

An Approach to a Ductility Criterion. The capacity of materials for plastic deformation notably helps prevent component failures. As yet, no criterion exists for the ductility requirement to be imposed. A theorem is here proposed to assist in the determination of the ductility requirement by assessing five load characteristics. These characteristics are: utilization of the material, unsafety of the load assumption, energy absorption requirement, complexity of component configuration, and safety requirement.     

Entwicklung und Anwendung von mathematischen Optimierungsmethoden zur Ableitung von vereinfachten Prüfungen für Fahrwerksbauteile

Testing the fatigue life time of chassis components is necessary during the development process and for quality supervision during the period of series production. In many cases a simplified test is done to reduce the complexity of the test. The development engineer has to develop the specification of those simplified tests. According to the task different approaches are possible: Looking for an adaquate test load or for a simplified mounting ore both. This paper deals with several numerical methods for test specification development. Especially a numerical optimization routine is presented for detection of a signifcant load case. Also the iterative searching for a simplified mounting in combination with damage based selection of load channel is shown. Exemplary the application of the routines is demonstrated by Porsche PANAMERA wheel carrier and a suspension‐strut receiving. The actual stage of development of the numerical routines is presented. In addition intended upgrades of the software are shown.