R-Curve Behavior and Crack-Closure Stresses in Barium Titanate and (Mg,Y)-PSZ Ceramics

R -curves, process zones, and shielding stresses of barium titanate (BaTiO₃) and partially stabilized zirconia (PSZ) have been studied using compact-tension (CT) specimens. BaTiO₃ and PSZ exhibited pronounced R -curves that rose over similar crack lengths and showed steady-state toughnesses of 0.7 and 6.4 MPa·m^1/2, respectively. Both steady-state toughnesses were ∼80% larger than the initial fracture toughnesses. Ferroelastic domain switching was the main toughening mechanism in BaTiO₃, whereas, in PSZ, transformation toughening was the main toughening mechanism. The crack process zone and crack-opening-displacement (COD) profile of each material was studied in detail using atomic force microscopy. Crack-closure-stress distributions were extracted from the COD profiles, using weight-function methods. The resulting stress profiles indicated that compressive residual stresses of 40 MPa in BaTiO₃ and 400 MPa in PSZ acted in a limited region behind the crack tip. In the PSZ, crack bridging seemed to be a competing mechanism to transformation toughening.     

Investigation on induction heating for hot stamping of boron alloyed steels

Within hot stamping of quenchenable steels the blank is heated up to austenitization temperature, transferred to the tool, formed rapidly and quenched in the cooled tool. Essential for the complete process is the heating of the blank which is currently carried out with roller hearth furnaces. As a consequence of rising energy costs new and more time and energy effective heating systems are needed. The paper presents investigations on induction heating as an alternative heating technology. Results concerning the process windows as well as material characteristics and grain structure will be presented and discussed.     

Vitamin E-Stoffwechsel der Lunge

Vitamin E Metabolism of the Lung . Experimental and clinical data have provided evidence for the involvement of oxygen free radicals in the development of acute and chronic lung diseases. Alveolar surfactant is the prime target of oxidative air pollutants. Lung surfactant consists to 90% of lipids and contains vitamin E as most important lipophilic antioxidant. Recently, we showed that alveolar surfactant is supplemented with vitamin E during its synthesis in type II pneumocytes. Hyperoxia is very often a necessary therapeutic intervention which seems to impose oxidative stress on lung tissue. Hyperoxia caused an increase in vitamin E turnover, measured in type II pneumocytes, lamellar bodies and lung lavages. In contrast, the turnover of surfactant cholesterol and surfactant lipids does not change. Hyperoxia caused an increase in vitamin E uptake by type II pneumocytes an enrichment of vitamin E in lamellar bodies.     

Forming operation of metastable austenitic stainless steel and inductive recrystallization of strain induced martensite

The temperature assisted recrystallization of strain induced martensite, after deep drawing metastable austenitic stainless steels, is a well known process for increasing the formability through multi-level deep drawing applications. State of the art recrystallization processes, using continuous annealing or vacuum furnaces, have the disadvantage of variable grain growth over the part cross section. This paper shows how the heat treatment by using an electro magnetical field, provided through different types of induction coils, can affect material properties positively. The studies were carried out on AISI 304 specimens with varied strain rates     

Communication with patients

The role of nitric oxide (NO) as a bronchodilator has been studied in humans with controversial results. The aim of the present study was to investigate the role of endogenous NO on bronchial tone by studying whether nitric oxide synthase (NOS) inhibition with NGnitro-L-arginine-methyl-ester (L-NAME) influences basal bronchial tone, or potentiates methacholine-induced bronchoconstriction. In a preliminary experiment in five subjects, a significant reduction in exhaled NO was found after delivering L-NAME (15 mg in saline) (from 3.9 +/- 1.2 to 2.4 +/- 1.1 nmol min-1, P < 0.05). In nine healthy non-smokers, specific airway conductance (SGAW), as a measure of airway calibre, was recorded after delivering, in a double-blind, controlled vs. placebo fashion, both nebulized L-NAME and saline, at baseline and after methacholine-induced bronchoconstriction. There was no significant difference between the baseline SGAW values before and after delivering L-NAME (0.264 +/- 0.04 and 0.267 +/- 0.05 cm H2O-1 s-1, respectively). After pre-treatment with L-NAME, SGAW values during methacholine-induced bronchoconstriction were not different in comparison to values obtained after saline inhalation. It is concluded that decreased endogenous NO does not influence bronchial tone in healthy people, nor does it modify methacholine-induced bronchoconstriction.     

Investigation of a combined micro-forming and punching process for the realization of tight geometrical tolerances of conically formed hole patterns

The outer shaving foils in electrical shavers are made from nickel through a galvanic deposition process, which are the subject of restrictions to eliminate allergic hypersensitivity to nickel. The substitution of this material through a stainless steel would require new manufacturing technologies to meet such parts’ specifications. Narrow patterns of micro holes with raised edges smaller than Ø0.53 mm were punched into a 1.4310 sheet having a tensile strength of 1200 MPa. This paper summarizes the process development and presents the results gained through a feasibility study. Experimental investigations were carried out with special concern to the influence of punch and die geometry on process forces and finished part accuracy.     

Direct laser deposition of Cu alloy on forming tool surfaces—Process window and mechanical properties

Direct laser deposition offers a widespread spectrum of applications. Creating functional surfaces for forming tools is one of them where inexpensive material for the main tool body is complemented layer by layer with a second material to tune the desired properties and shape. Investigations on coating mild tool steel with copper alloy have been carried out to outline the chances and challenges in this cost effective way of producing forming tools for processing stainless steels, e.g. 1.4301. This paper reports on experimental investigations showing the influence of the absolute angle of the tool surface and the relative angle between surface and laser beam/powder nozzle on the process window and the mechanical properties that can be obtained.