Steady-State Creep Analysis of Pressurized Pipe Weldments by Perturbation Method

The stress analysis of pressurized circumferential pipe weldments under steady state creep is considered. The creep response of the material is governed by Norton's law. Numerical and analytical solutions are obtained by means of perturbation method, the unperturbed solution corresponds to the stress field in a homogeneous pipe. The correction terms are treated as stresses defined with the help of an auxiliary linear elastic problem. Exact expressions for jumps of hoop and radial stresses at the interface are obtained. The proposed technique essentially simplifies parametric analysis of multi-material components.Comment: 17 pages, 6 figure

Edge Effects in Moderately Thick Plates under Creep-Damage Conditions

The late F.P.J. Rimrott has published during his scientific life more than 200 refereed articles and conference papers. Various papers among them were devoted to the creep and plasticity analysis in metallic thin-walled structural elements mostly published in the period from 1958 till 1964. With regard to this early period below we discuss finite element solutions for moderately thick plates under creep-damage conditions based on shell and solid type finite elements. The results illustrate the time-dependent stress redistributions in the edge zones. We show that the transverse normal and shear stresses may have a significant influence on the damage evolution and must be considered in numerical lifetime estimations

Structure-function analysis of plant fructosyltransferases

Fructans are an important class of plant carbohydrates that consist of linear or branched chains of fructosyl moieties. Their synthesis requires fructosyltransferases (FTs) that catalyze the transfer of fructosyl units from a donor substrate (sucrose or fructan) to an acceptor substrate (sucrose or fructan). The fructosyltransferases involved in fructan metabolism are related to acid invertases, enzymes that cleave sucrose into glucose and fructose. An invertase can be considered a fructosyltransferase which transfers the fructose moiety to water. The aim of the present work was to elucidate what determines the different catalytic activities of this enzyme group, by use of molecular methods. In order to study such structure-function relationships we artificially introduced mutational changes and constructed chimeric FTs (enzymes with exchanged regions). The goal was to detect the determining regions or single amino acids. For this purpose we optimized the expression of FTs in the methylotrophic yeast Pichia pastoris and developed the methodology to create the chimeric constructs. Conventional cloning using conveniently located restriction sites and the method of overlapping PCR was used. In a first part domain exchanges between two closely related FTs from cereals were analyzed by expressing the corresponding constructs in Pichia (Chapter 2). The two subunits of FTs (N-terminal large subunit and C-terminal small subunit) were exchanged between Festuca arundinacea (re-classified as Schedonorus arundinaceus) sucrose:sucrose 1-fructosyltransferases (1-SST) and Hordeum vulgare sucrose:sucrose 6- fructosyltransferase (6-SFT). The study revealed that it is the large subunit that carries the structural features responsible for enzyme specificity. In a second part we focused on the conserved motifs (S/N)DPNG, RDP and EC, located on the large subunit, that are presumably essential in the active site of plant FTs. For this purpose two other SST-SFT-chimeras with exchanged N-termini encompassing these motifs, as well as Festuca 1-SST carrying single amino acid substitutions in the RDP- and EC-motif were analyzed (Chapter 3). This study revealed the importance of the three hypothesized active site motifs for the transfructosylation reaction. All three of them were shown to be important for enzyme activity and/or for specificity. In a third part, we addressed the question what structural components determine the relative transferase and hydrolase activities of FTs and vacuolar invertases via a targeted mutational analysis based on sequence comparisons between vacuolar invertases and 1-SSTs, the latter an example of a sucrose-using FT (Chapter 4). We chose Allium cepa invertase and Festuca arundinacea 1-SST for our analysis. Nine amino acids dispersed along the sequence could be identified correlating with either invertase or 1-SST activities. The selected amino acids of onion invertase were mutated to the corresponding amino acids in Festuca 1-SST and vice versa. For both enzymes, the mutations were analyzed independently. Functional expression in Pichia revealed shifts in the catalytic specificity and activity, demonstrating the importance of these amino acids outside the three highly conserved motifs (S/N)DPNG, RDP, and EC for the enzymatic reaction (Chapter 4). This work helped to narrow down the region potentially responsible for enzyme specificity in plant FTs. We could pinpoint the importance of the regions with the highly conserved motifs, and of some additional characteristic single amino acids dispersed along the sequence, for enzyme activity and specificity

Social Media in the Classroom

The question that guided this study is: how can we use social media that our students are already fluent in, to engage them more in the classroom? The purpose of the study was to find out if teachers in the district where I work are using social media in their classrooms and if not, what objections or hesitations they have with social media. For the procedures, I interviewed elementary teachers in the district where I work, about how they use social media in their classroom and possible objections or challenges they might face in its use in the classroom. I was able to get the perspectives of 10 teachers, spanning grade levels of Kindergarten to Sixth Grade. The findings that were discovered from my data analysis were: 1) forms of social media are already being implemented, 2) teachers feel supported with the technology in their classrooms, 3) teachers view their tech savvy students as a positive, 4) despite concerns, most teachers recommend using social media for teachers. I was able to conclude from the findings that teachers are implementing a variety of social media modes successfully and see how it is positively impacting their students, and the objections that teachers have with using social media in their classrooms seems to be validated by research studies

Longitudinal fracture analysis of inhomogeneous beams with continuously varying sizes of the cross-section along the beam length

Analyses of longitudinal fracture behavior of inhomogeneous beams which have continuously varying sizes of the cross-section along the beam length are carried-out. Beams of a rectangular cross-section are studied. It is assumed that beams exhibit continuous (smooth) material inhomogeneity along the width and height of the cross-section. A longitudinal crack located arbitrary along the beam height is analyzed. First, a cantilever beam with linearly varying width and height along the beam length is considered. The material of the beam has non-linear elastic mechanical behavior. The external loading consists of one bending moment applied at the free end of the lower crack arm. The fracture behavior is analyzed in terms of the strain energy release rate assuming that the modulus of elasticity is distributed continuously in the beam cross-section. The balance of the energy is considered in order to derive the strain energy release rate. A solution to the strain energy release rate is obtained also by considering the complementary strain energy for verification. The longitudinal fracture behavior of the inhomogeneous non-linear elastic cantilever beam configuration is studied also for the cases when the variation of the width and height of the cross-section is described by sine and power laws.      &nbsp

Eigen-vibrations of Plates made of Functionally Graded Material

Within the framework of the direct approach to the plate theory we consider natural oscillations of plates made of functionally graded materials taking into account both the rotatory inertia and the transverse shear stiffness. It is shown that in some cases the results based on the direct approach differ significantly from the classical estimates. The reason for this is the non-classical computation of the transverse shear stiffness

30 Years of the Journal Technische Mechanik

In 1980 Technische Mechanik started being published as a new scientific journal after long and complicated negotiations with the authorities of the former GDR. The most powerful argument at the time was that mechanics research could contribute significantly to technological and industrial development within mechanical and process engineering, shipbuilding, civil engineering, etc. Improvements in structural and material design, stability and durability, and life-time prediction were expected to lead to savings of material, and better protection of natural resources and the environment, and would, thus, have a more positive impact on the economic strength of the country

Longitudinal Fracture Analysis of an Inhomogeneous Stepped Rod with Two Concentric Cracks in Torsion

Analysis of the longitudinal fracture behaviour of an inhomogeneous stepped rod with two concentric longitudinalcracks is developed. The stepped rod has circular cross-section and exhibits continuous material inhomogeneity in radial direction.The material has non-linear elastic mechanical behaviour. The rod is subjected to torsion. The two cracks present concentriccircular cylindrical surfaces. Thus, the fronts of the cracks are circles. The fracture is studied in terms of the strain energy releaserate by considering the complementary strain energy stored in the rod. Solutions to the strain energy release rate are derived atdifferent lengths of the two cracks. The balance of the energy is analyzed in order to verify the solutions. It is shown that thesolutions can be applied also when the stepped rod is inhomogeneous in both radial and length directions. The solutions are usedin order to evaluate the influences of the locations of the two concentric cracks in radial direction and the material inhomogeneityin radial and length directions on the longitudinal fracture behaviour of the stepped rod