Beitrag zur vereinfachten Biegebemessung von FVK‐bewehrten Holzträgern

Contribution to a simplified bending design model for FRP reinforced glulam beams. Based on a research report by Blaß/Romani (2000) a simplified model is developed for the design of a bending beam made of glulam and a longitudinal reinforcement on the tension side by a fibre reinforced plastic (FRP) lamella. In case of the reinforcement placed inside the wood (typeN) the calculation is based on bonding theory, in case of the reinforcement placed on the edge (typeR) the calculation should be handled both according to bonding theory and approximately analogous to a cracked reinforced concrete cross‐section. The proposed model is compared with a similar one introduced by Blaß/Romani (2000). It is shown, that by some essential simplifications with only negligible effects on the results one can yield a lower calculation effort and a higher degree of clarity. Comparing with test results from the report of Blaß/Romani the results of the extended approach for typeR even fit better.     

Determination of extended availability and productivity for assembly systems using existing data base

Reliable information about the operational availability of assembly or production systems is of great importance for the users of complex production facilities, especially when such facilities operate at their capacity limit. Nowadays, in most cases, the availability of assembly systems is monitored and evaluated using collected status data. This paper presents a new approach for permanent productivity determination of assembly systems based on the usage of in-process acquired product data. This approach is especially applicable for manufacturing systems that produce goods for which complete product traceability is required.     

Metrological solutions for an adapted inspection of parts and tools of a sheet-bulk metal forming process

Processes of the new production technology sheet-bulk metal forming allow a fast and efficient near-net-shape forming of highly complex parts. Thus the need of energy and raw material as well as the production cycle time can be reduced. In order to guarantee these advantages by avoiding scrap and moreover to ensure the parts’ geometrical requirements, production-related metrological solutions for an adapted inspection of parts and tools of sheet-bulk forming processes have to be developed. To fulfill the demands of the differing measuring tasks two prototypical measurement solutions are under development: a multi-scale multi-sensor fringe projection system allows for holistic inspections in feature adapted resolutions, whereas a fiberscopic fringe projection system captures the forming tool partly between forming steps. For the purpose of evaluating the metrological solutions’ capabilities of capturing the geometry of filigree structures a comparison of both systems is presented in this work. To guarantee realistic results, the performed measuring tasks have to be comparable to the areas of applications both systems were designed for. During the development of the measuring systems the emphasis was put on the inspection of small complex geometries. These are most challenging for fast and reliable optical inspection under production-related conditions. By considering measurements of calibrated standards on the one side as well as of measuring tasks resulting out of real sheet-bulk metal forming processes on the other side a realistic comparison is assured. Next to the measuring systems’ performances also an approach for combining the measurement data of both metrological solutions is shown. By combining the advantages of both measuring systems, highly detailed information for further interpretations of the forming processes can be provided.     

Thoracic CT in the intensive care unit: assessment of clinical usefulness

PURPOSE: To enlarge the prostatic urethra with thermal coagulation with transrectal radio-frequency (RF) application in dogs. MATERIALS AND METHODS: Eight aged dogs underwent RF ablation of periurethral prostatic tissue for 6 minutes. Eighteen-gauge electrodes were placed into the periurethral tissues with a transrectal approach and ultrasound (US) guidance. Prostatic and rectal temperatures were measured during RF application. US, conventional and computed tomographic (CT) retrograde urethrography (RUG), and CT were performed immediately (n = 8) and at 3-96 days (n = 6) after ablation. Histopathologic analysis was performed at sacrifice immediately (n = 2), at 28 days (n = 2), or at 3 months (n = 4) after treatment. RESULTS: All procedures were successful with no complications and were performed in less than 30 minutes. Rectal mucosal temperature did not exceed 38 degrees C. Immediately after treatment, CT and US demonstrated 1.2-cm foci of altered periurethral tissue that corresponded to solid coagulated tissue at histopathologic analysis. By day 3, CT, RUG, and US demonstrated that these foci had begun to cavitate, resulting in enlargement of the urethra. Complete cavitation was demonstrated by day 28. Minimal reduction in the degree of urethral enlargement was noted by day 60, but narrowing, urethral strictures, or fistulas were not observed at 3 months. At histopathologic analysis, focal cavitary enlargement with at least doubling of the urethral diameter and with normal urothelium was noted in all dogs surviving at least 28 days. CONCLUSION: Transrectal RF urethral enlargement is feasible and safe in animals and merits investigation for alleviating urethral obstruction due to benign prostatic hyperplasia.     

Experimental and numerical studies on the braiding of carbon fibres over structured end-fittings for the design and manufacture of high performance hybrid shafts

Braiding is an attractive manufacturing method for tubular elements such as hollow shafts and struts. One of the main challenges however is the integration of suitably performing end-fittings. Recent advances in additive layer manufacture have enabled the fabrication of end-fittings which can be ‘co-impregnated’ or ‘co-cured’ with the fibre preform in a single step, i.e. without the need for secondary adhesive bonding. This requires the introduction of protrusions onto the surface of the end-fitting to promote mechanical interlocking with the fibres. However, the lack of accurate modelling tools for the simulation of this manufacturing process means that much empiricism is currently used in the design of such structures. A novel numerical framework is presented here for the full-scale simulation of the braiding process over structured end-fittings. Nonlinear finite element analysis is applied at the meso-scale, with strands of beam elements representing individual yarns and meshed surfaces modelling the mandrel and tooling. Penalty-based contact formulations are then used to simulate all inter-yarn and yarn-metal interactions, enabling detailed predictions of fibre paths around surface protrusions. In order to verify and validate this numerical framework, a series of full-scale braiding experiments was conducted using additively-manufactured thermoplastic mandrels. Final braid patterns as well as the occurrence of braid imperfections were investigated and compared to model predictions. It is shown that the proposed modelling strategy reproduces well the trends observed experimentally in terms of final braid quality. A parametric study was then conducted on the effects of initial end-fitting alignment with respect to oncoming yarns, suggesting that better control over this parameter could reduce considerably the occurrence of braid imperfections.     

Comparing methods for measuring consumer willingness to pay for a basic and an improved ready made soup product

Willingness to pay (WTP) for a basic chilled soup product and for an improved, self-heating version was measured by methods experimentally varied according to a 2 × 3 design, varying the basic measurement approach (contingent valuation, experimental auction, conjoint analysis) and the use of real vs. game money. Measurement protocols for each approach were adapted in order to allow uniform methods factors across the design. WTP was measured for 551 shoppers recruited in a shopping centre, using personal interviewing and closed questioning. Shoppers in the real money condition received an endowment at the beginning of the task. Drawing on constructs derived from research in consumer price information processing, subject’s reference price, price involvement, and price thought style were also measured. Results showed no differences between use of contingent valuation and experimental auction, and between the use of real vs. game money. Conjoint analysis led to lower WTP estimates for the product improvement than the other two methods Reference price and one dimensions of price involvement – value consciousness – were related to WTP estimates for the base product.     

Comparing the results from various performance models of IEEE 802.11g DCF

IEEE 802.11 DCF is the most widely-used CSMA/CA access control mechanism. Recent analytic performance models for DCF have received acclaim for both their simplicity and reported accuracy. Most of these models share the assumptions of full single-hop connectivity among all stations, that DCF back-off may be modeled as a Markov process and that the network is saturated with traffic. In order to verify the accuracy of existing analytic models we developed a discrete-event simulator to record the performance of the DCF protocol and ensure that every detail of the standard is represented. Simultaneously we set up a hardware test bed to measure the same performance metrics in an environment that makes none of the simplifying assumptions of either the analytic models or the simulation. In the test bed, as in the simulator, we used the same physical parameter settings prescribed by the standard. As is the case for the analytic models we used, we subjected the simulator and the test bed to the same saturated workload for both basic and RTS/CTS access modes. Finally, we also implemented a non-saturating Markov Modulated Arrival Process (MMAP) workload model for our simulator to test the performance of DCF subject to more realistic internet traffic conditions. We describe both the simulator and the test bed in some detail in order to testify to the accuracy and detail of our results. The results show that the analytic models are mostly pessimistic for small numbers of nodes and optimistic for larger numbers of nodes. The performance measurements from the test bed, in turn, indicate that the simulation results are similarly optimistic when large numbers of nodes are concerned. Since the test bed uses an error-prone wireless channel, this latter result is, in principle, not surprising. The rate of deterioration in the actual performance is however something that is not widely known and is much more rapid than analytic models would suggest.