Experimentelle und numerische Ermittlung dynamischer Risswiderstandskurven im Kerbschlagbiegeversuch

Experimental and numerical determination of crack resistance curves in the notched‐bar impact test The assessment of the reliability of components requires the knowledge of crack resistance curves, which are often not available due to lack of specimen material. More likely is the availability of typical material parameters such as the yield strength, tensile strength, uniform elongation, elongation at rupture as well as upper shelf impact energy and the lateral elongation of notched‐bar impact test specimens. The material model of Gurson describes ductile crack growth due to the nucleation, growth and coalescence of voids in the material. Although dependent on the material and temperature, the material parameters of the Gurson model are independent of the specimen geometry and rate of loading. This latter fact allows one to use the values of these parameters determined on statically‐loaded fracture mechanics specimens to model specimens with other geometries and subjected to different loading conditions, in particular to model impact loaded Charpy‐V specimens. A method is proposed to construct crack resistance curves based on available data of tension tests and on quasi‐static yield curves. Dynamic yield curves are determined using proven procedures as based on the analysis of the dislocation activation energy. The ductile damage parameters are then obtained via simulation of tests on notched tensile specimens and notched‐bar impact tests as well as the fitting to the upper shelf impact energy. In this way, the ductile damage parameters are determined, which in turn enable the determination of the required J‐resistance curves via simulation of ductile crack growth in fracture mechanics specimens. Thus, the application of the classical J‐integral concept gets possible. Furthermore, the independence of the identified material parameters from the geometry of the specimen then allows the use of the Gurson model to analyse the safety of structural components with cracks directly.     

Identification of a novel dihydrolipoyl dehydrogenase-binding protein in the pyruvate dehydrogenase complex of the anaerobic parasitic nematode, Ascaris suum

A novel dihydrolipoyl dehydrogenase-binding protein (E3BP) which lacks an amino-terminal lipoyl domain, p45, has been identified in the pyruvate dehydrogenase complex (PDC) of the adult parasitic nematode, Ascaris suum. Sequence at the amino terminus of p45 exhibited significant similarity with internal E3-binding domains of dihydrolipoyl transacetylase (E2) and E3BP. Dissociation and resolution of a pyruvate dehydrogenase-depleted adult A. suum PDC in guanidine hydrochloride resulted in two E3-depleted E2 core preparations which were either enriched or substantially depleted of p45. Following reconstitution, the p45-enriched E2 core exhibited enhanced E3 binding, whereas, the p45-depleted E2 core exhibited dramatically reduced E3 binding. Reconstitution of either the bovine kidney or A. suum PDCs with the A. suum E3 suggested that the ascarid E3 was more sensitive to NADH inhibition when bound to the bovine kidney core. The expression of p45 was developmentally regulated and p45 was most abundant in anaerobic muscle. In contrast, E3s isolated from anaerobic muscle or aerobic second-stage larvae were identical. These results suggest that during the transition to anaerobic metabolism, E3 remains unchanged, but it appears that a novel E3BP, p45, is expressed which may help to maintain the activity of the PDC in the face of the elevated intramitochondrial NADH/NAD+ ratios associated with anaerobiosis.     

For whom size matters – the interplay between incubator size,tenant characteristics and tenant growth

The present study introduces a multilevel ‘fit’ perspective on business incubation to examine the link between incubator size and tenant growth. We suggest that the effect of incubator size on tenant growth is not universally positive or negative but is contingent upon (a) the size of the tenants’ venture team and (b) whether tenants are operating in a high-tech industry. Based on data from 276 tenants hosted in 67 business incubators in Germany, multilevel analyses provide support for our hypotheses. With its findings, the present study complements earlier incubator research and expands our knowledge on which types of business incubators are best suited to facilitate venture development.     

The calculation of dynamic JR-curves from the finite element analysis of a Charpy test using a rate-dependent damage model

A two-dimensional analysis of the Charpy V-notch specimen subjected to impact loading, according to the standard DIN EN 10045-1, is carried out, using a transient explicit dynamic finite element program. An elastic-viscoplastic, temperature dependent, constitutive relation for a porous plastic solid based on the Gurson damage model is developed. Ductile fracture of the matrix material will be described by the nucleation and subsequent growth of voids to coalescence. An updated Lagrange–Jaumann formulation is employed accounting for large strain and rotation. The discretization is based on four-node plane strain solid elements with one Gauss point. The equations of motion are integrated numerically by an explicit integration algorithm utilising a lumped mass matrix. The predictions of the numerical analysis in terms of force deflection response, crack resistance behaviour and deformation energy absorbtion are compared with results from Charpy tests which were carried out according to the low-blow technique.     

Continuous delamination of sprayed deposits via applied curvature

In this work, the delamination of a bimaterial interface continuously subjected to an applied curvature is considered for direct application to the controlled debonding of sprayed metal deposits. Important to the success of some spraying applications is the ability to systematically remove sprayed deposits from their substrates. A method for doing so is described, in which the deposit is sprayed onto a relatively thin substrate, which is subsequently conveyed along a curved path so that the deposit is continuously delaminated from the substrate. In this work, the continuous delamination of a sprayed metal deposit via an applied curvature is studied as a two-dimensional interfacial fracture mechanics problem. A closed-form solution for the steadystate energy release rate governing interfacial fracture is determined. A finite element model is used to verify the analytical prediction, as well as to extract a measure of mode mix. For the case of a substrate that is both thin and stiff relative to the deposit, the mode-mix admits a simplified approach to measuring interfacial toughness values for prospective deposit/substrate combinations. Straightforward analytical design guidelines are presented and are used to investigate the feasibility of the delamination process.     

Determination of dynamic crack resistance of ductile cast iron using the compliance ratio key curve method

The compliance ratio method is an analytical approach for instantaneous crack length determination in dynamic single-specimen J-R curve testing of ferritic ductile cast iron (DCI). Comparison testing at room temperature and −40 °C was applied to PCVN and SE(B)15 specimens to examine their performance and suitability for the dynamic key curve method for DCI. An experimental reference database of dynamic crack resistance curves was set up by low-blow multiple-specimen tests and used to validate the results of the CR method. The influence of test temperature, microstructure, loading rate and specimen geometry on fracture behavior of the tested DCI was investigated in great detail and these parameters were linked to fracture mechanical properties. The results obtained show that the CR method is suited to establish valid dynamic crack resistance curves for both types of specimen. Nevertheless, SE(B)15 specimens are preferred for dynamic J-R curve determination of DCI based on their advantages such as higher accuracy.     

Open and short circuits in coplanar MMIC's

Coplanar MMIC stub configurations are investigated by means of the finite-difference method in the frequency domain. The open end, the short end, and a capacitively loaded short end (MIM-short) are analyzed. Their parasitic effects are described in terms of the effective length extension l_ext. The influence of the different line parameters is discussed and simple design rules are given