Technische Universität Darmstadt

About: Technische Universität Darmstadt is a education organization based out in Darmstadt, Germany. It is known for research contribution in the topics: Computer science & Context (language use). The organization has 17316 authors who have published 40619 publications receiving 937916 citations. The organization is also known as: Darmstadt University of Technology & University of Darmstadt.

Strain-softening of concrete in uniaxial compression

Abstract: 0025-5432/97 © RILEM tory cast its own specimens following a prescribed recipe The pre-peak behaviour was found to be independent of specimen slenderness when low friction loading platens were used However, for all loading systems a strong increase of (post-peak) ductility was found with decreasing specimen slenderness Analysis of the results, and comparison with data from literature, showed that irrespective of the loading system used, a perfect localization of deformations occured in the post-peak regime, which was first recognised by Van Mier in a series of uniaxial compression tests on concrete between brushes in 1984 Based on the results of the Round Robin, a draft recommendation will be made for a test procedure to measure strain softening of concrete under uniaxial compression Although the post-peak stress-strain behaviour seems to be a mixture of material and structural behaviour, it appears that a test on either prismatic or cylindrical specimens of slenderness h/d = 2, loaded between low friction boundaries (for example by inserting sheets of tef lon between the steel loading platen and the specimen), yields reproducible results with relatively low scatter For normal strength concrete, the closed-loop test can be controlled by using the axial platen-to-platen deformation as a feed-back signal, whereas for high-strength concrete either a combination of axial and lateral deformation should be used, or a combination of axial deformation and axial load FOREWORD An extensive Round Robin test programme on compressive softening was carried out by the RILEM Technical Committee 148-SSC “Test methods for the Strain Softening response of Concrete” The goal was to develop a reliable standard test method for measuring strain softening of concrete under uniaxial compression The main variables in the test programme were the specimen slenderness h/d and the boundary restraint caused by the loading platen used in the experiments Both high friction and low friction loading systems were applied Besides these main variables, which are both related to the experimental environment under which softening is measured, two different concretes were tested: a normal strength concrete of approximately 45 MPa and a higher strength concrete of approximately 75 MPa In addition to the prescribed test variables, due to individual initiatives, the Round Robin also provided information on the effect of specimen shape and size The experiments revealed that under low boundary friction a constant compressive strength is measured irrespective of the specimen slenderness For high friction loading systems (plain steel loading platen), an increase of specimen strength is found with decreasing slenderness However, for slenderness greater than 2 (and up to 4), a constant strength was measured The shape of the stress-strain curves was very consistent, in spite of the fact that each laboraRILEM TC 148-SSC: TEST METHODS FOR THE STRAIN-SOFTENING RESPONSE OF CONCRETE

Algorithms for Multi-exponentiation

Abstract: This paper compares different approaches for computing power products Π1≤i≤k giei in commutative groups. We look at the conventional simultaneous exponentiation approach and present an alternative strategy, interleaving exponentiation. Our comparison shows that in general groups, sometimes the conventional method and sometimes interleaving exponentiation is more efficient. In groups where inverting elements is easy (e.g. elliptic curves), interleaving exponentiation with signed exponent recoding usually wins over the conventional method.

Constrained sintering: A delicate balance of scales

Abstract: Sintering is a common technique for the production of ceramic, metallic and composite bodies and components. During this process it is known that internal stresses can arise from external constraint or from differential densification. These stresses can give rise to significant strain rate changes, distortions and damage in the fired parts. For quality control of sintered bodies, it is necessary to measure or predict the changes in deformation behaviour that occurs as the porous starting bodies undergo densification. Contributions of the continuum mechanical approach to this problem of constrained sintering are reviewed. Theoretical predictions as well as experimental techniques and results are detailed. Special emphasis is given to the development of anisotropy that can develop in the microstructure of a sintering body in response to the internal stresses.

Human factors in order picking: a content analysis of the literature

Abstract: Order picking (OP) is one of the most labour- and time-intensive processes in internal logistics Over the last decades, researchers have developed various mathematical planning models that help to increase the efficiency of OP systems, for example, by optimising storage assignments or by specifying routes for the order pickers that minimise travel distance in the warehouse Human characteristics that are often a major determinant of OP system performance have, however, widely been ignored in this stream of research This paper systematically evaluates the literature on manual OP systems and conducts a content analysis to gain insights into how human factors (HF) have been considered and discussed in the scientific literature The results of the analysis indicate that management-oriented efficiency criteria dominated prior research on OP, and that there is a clear lack of attention to HF in the design and management of OP systems This poses an opportunity for research and design of manual OP systems

A two-parameter criterion for classifying the explodability of massive stars by the neutrino-driven mechanism

Abstract: Thus far, judging the fate of a massive star (either a neutron star (NS) or a black hole) solely by its structure prior to core collapse has been ambiguous. Our work and previous attempts find a non-monotonic variation of successful and failed supernovae with zero-age main-sequence mass, for which no single structural parameter can serve as a good predictive measure. However, we identify two parameters computed from the pre-collapse structure of the progenitor, which in combination allow for a clear separation of exploding and non-exploding cases with only few exceptions (~1-2.5%) in our set of 621 investigated stellar models. One parameter is M4, defining the normalized enclosed mass for a dimensionless entropy per nucleon of s=4, and the other is mu4 = d(m/M_sun)/d(r/1000 km) at s=4, being the normalized mass-derivative at this location. The two parameters mu4 and M4*mu4 can be directly linked to the mass-infall rate, Mdot, of the collapsing star and the electron-type neutrino luminosity of the accreting proto-NS, L_nue ~ M_ns*Mdot, which play a crucial role in the "critical luminosity" concept for the theoretical description of neutrino-driven explosions as runaway phenomenon of the stalled accretion shock. All models were evolved employing the approach of Ugliano et al. for simulating neutrino-driven explosions in spherical symmetry. The neutrino emission of the accretion layer is approximated by a gray transport solver, while the uncertain neutrino emission of the 1.1 M_sun proto-NS core is parametrized by an analytic model. The free parameters connected to the core-boundary prescription are calibrated to reproduce the observables of Supernova 1987A for five different progenitor models.