Der Einfluß einer Vorreckung auf das Knickverhalten von normalgeglühtem Stahl Ck45

Knickversuche an Proben aus normalgeglühtem Stahl Ck45. Einfluß einer Vorreckung auf die ertragbare Knickspannung. Ermittlung von Sekantenmoduln und Tangentenmoduln nach unterschiedlich starken Vorverformungen. Vergleich experimenteller Knickkenngrößen mit der theoretischen Erwartung aufgrund des Druckverformungsverhaltens.     

Chromosomal aberrations in couples undergoing intracytoplasmic sperm injection: influence on implantation and ongoing pregnancy rates

Mononitrosocaffeidine (MNC) and dinitrosocaffeidine (DNC) are new N-nitroso compounds obtained from in vitro nitrosation of caffeidine, a hydrolysis product of caffeine present in a typically made and widely consumed tea from Kashmir (India), a high incidence area of esophageal and stomach cancer. The chemical synthesis, in vitro metabolic studies and mutagenicity of the compounds has been previously reported. DNC, a nitrosamide is highly mutagenic both with and without metabolic activation whereas MNC, like several other aromatic asymmetric nitrosamines, does not exhibit genotoxic or mutagenic properties. We now report the results of the first carcinogenicity experiments on chronic oral administration of these compounds in BD-IX rats. The acute LD50 of MNC and DNC were about 1300 and 230 mg/kg b.w., respectively. Lung oedema and gastrointestinal haemorrhages were the first symptoms of intoxication observed after 2 days for both the compounds. All three dose groups of MNC treated rats showed localization of tumours in nasal cavity (93.9-100% of all malignant tumours). The tumours were histologically diagnosed as neuroepitheliomas of the olfactory epithelium (neuroblastoma of the bulbus olfactorii) and squamous cell carcinoma of the nasal cavity in the ratio of 3:1. No tumours of the nasal cavity were observed in the untreated controls. DNC, in contrast, induced squamous cell carcinoma of forestomach in 100% animals at low and high doses, of which nearly half the tumours metastasized predominantly into the peritoneum. No forestomach tumours were seen in the untreated controls. The data presented here clearly show the potential for induction of malignant tumours and distinct organ-specificity by MNC and DNC in rats, and support the postulate that a chronic exposure to these compounds may provide a carcinogenic risk for high incidence of gastrointestinal cancers in Kashmir.     

Verhalten laserschockverfestigter und festgewalzter Randschichten der Ti‐Legierung Ti‐6Al‐4V bei schwingender Beanspruchung unter erhöhten Temperaturen

Residual stress stability and near‐surface microstructures in high temperature fatigued mechanically surface treated Ti‐6Al‐4V It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly‐stressed metallic components. Deep rolling is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of deep rolling on the low‐cycle and high‐cycle fatigue behavior of a Ti‐6Al‐4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near‐surface microstructures. Preliminary results on laser shock peened Ti‐6Al‐4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ～450 °C, i.e., at an homologous temperature of ～0.4 T/T_m (where T_m is the melting temperature). Based on cyclic deformation and stress/life (S/N) fatigue behavior, together with the X‐ray diffraction and in situ transmission electron microscopy observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti‐6Al‐4V at such higher temperatures, despite the almost complete relaxation of the near‐surface residual stresses. In the absence of such stresses, it is shown that the near‐surface microstructures, which in Ti‐6Al‐4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment.     

Zur Ermittlung verformungsbedingter Makro- und Mikroeigenspannungen durch mechanische und röntgenographische Eigenspannungsanalysen

Analysis of deformation induced residual macro-and microstresses by mechanical and X-ray methods Residual stress distributions in plastically deformed tensile and bending specimens of perlitic steel were analysed using X-ray diffraction technique and incremental holedrilling method. After tensile loading compressive residual stresses are measured by X-ray analysis in the ferrite phase. Consequently X-ray analysis detects compressive microstresses. In the case of bending specimens residual macrostresses are superposed with residual microstresses after unloading. In no case identical residual stress values were measured by X-ray and hole drilling methods. Microstresses can be separated combining both measurement methods. Microstresses after tensile loading were found to be greater than in surface layers of respective bending samples subjected to the same amount of plastic strain.     

On the impact of deep rolling at different temperatures on the near surface microstructure and residual stress state of steel AISI 304

The consequences of deep rolling at cryogenic temperature, room temperature and high temperature were investigated for steel X5CrNi18‐10 (AISI 304). Near surface microstructures, martensite content and residual stresses were analyzed. It is shown that, applying different deep rolling temperatures, the near surface states of the processed specimen are altered in a characteristic way. Particularly important is that different depth distributions of strain hardening, martensite volume fraction and residual stresses can be created.     

DRG cost weight volatility and hospital performance

We develop a robust methodology which estimates the consequences of DRG cost weight volatility on hospital performance. The methodology is first developed using the hospital baserate as quantitative measure of hospital performance, then analyzed theoretically in the more general framework of cost-benefit analysis, and finally applied to two groups of hospitals. The first data set consists of a homogeneous group of 21 maximum-care hospitals in Germany and incorporates approximately 936,000 inpatient cases in 2003. The second data set consists of a heterogeneous group of 97 German hospitals and incorporates approximately 896,000 inpatient cases in 2003. The main finding is that the robust cost-benefit methodology developed in this study leads to results that are consistent with the theoretical background, since the hospital baserate spread in the more homogeneous group of hospitals is clearly lower than in the more heterogeneous group of hospitals. Our methodology illustrates the robustness of a hospital’s performance with respect to DRG cost weight changes and, therefore, represents a helpful tool in discussions about hospital budgets, strategic alliances, mergers, etc.     

On Morse Theory for Piecewise Smooth Functions

Lower level sets of continuous selections of C ²-functions defined on a smooth manifold in the vicinity of a nondegenerate critical point in the sense of [11] are studied. It is shown that the lower level set is homotopy equivalent to the join of the lower level sets of the smooth and the nonsmooth part, respectively, of the corresponding normal form. Some generalized Morse inequalities are deduced from this result.     

Consequences of transformation plasticity on the development of residual stresses and distortions during martensitic hardening of SAE 4140 steel cylinders

Residual stresses and distortions developing during martensitic hardening of steel can be quantitatively determined by finite element calculations, if the underlying processes are adequately modelled and the materials and process data necessary are known. In this context also transformation plasticity effects have to be taken into account. Model calculations for SAE 4140 steel cylinders demonstrate the influence of these effects on the developing residual stresses. Using a special device which allows martensitic transformation under constant external loads, for SAE 4140 the transformation plasticity constant K = 4.2 · 10^?5mm²/N is determined. With this constant and assuming realistic heat transfer conditions, the development of residual stresses and distortions of SAE 4140 cylinders with a diameter of 30 mm and a length of 90 mm is modelled. The calculated results are in good agreement with experimental findings.     

Energetic Materials: Crystallization,Characterization and Insensitive Plastic Bonded Explosives

The product quality of energetic materials is predominantly determined by the crystallization process applied to produce these materials. It has been demonstrated in the past that the higher the product quality of the solid energetic ingredients, the less sensitive a plastic bonded explosive containing these energetic materials becomes. The application of submicron or nanometric energetic materials is generally considered to further decrease the sensitiveness of explosives. In order to assess the product quality of energetic materials, a range of analytical techniques is available. Recent attempts within the Reduced‐sensitivity RDX Round Robin (R4) have provided the EM community a better insight into these analytical techniques and in some cases a correlation between product quality and shock initiation of plastic bonded explosives containing (RS‐)RDX was identified, which would provide a possibility to discriminate between conventional and reduced sensitivity grades.