Mechanical properties of thin films from the load deflection oflong clamped plates

A plane-strain load-deflection model for long plates clamped to a rigid support is developed. The analytical model describes the nonlinear deflection of plates with compressive or tensile residual stress and finite flexural rigidity under uniform load. It allows for the extraction of the residual stress and plane-strain modulus of single-layered thin films. Properties of compressively and weakly prestressed materials are extracted with an accuracy achieved previously only with tensile samples. Two approximations of the exact model are derived. The first reduces the plates to membranes by neglecting their flexural rigidity. Considerable errors result from this simplification. The second approximation provides an exact expression for the linear plate response. Using the model, mechanical properties were extracted from two plasma-enhanced chemical-vapor deposition (PECVD) silicon nitride films with weakly tensile and compressive prestress, respectively. Measured residual stresses are 1.3±3.8 and -63±12.4 MPa, respectively. Corresponding plane-strain moduli are 134.4±3.9 and 142±2.6 GPa, respectively     

Ein Ansatz zur Berücksichtigung der Bauteilform und Bauteilgröße bei Lebensdauervorhersagen

A Concept to Calculate Notch- and Size-Effect for Fatigue Life Prediction The fatigue behaviour of a specimen depends on its size and shape. To describe this, the following assumptions are made: There are flaws statistically distributed in the specimen. The largest of these flaws propagates during fatigue loading and forms the final crack. These two assumptions formulate a method for the calculation of the influence of specimen size and shape on fatigue life. This method is applied to own fatigue test results and to those presented in literature.     

Strongly buckled square micromachined membranes

The buckling of compressively prestressed square membranes with built-in edges is investigated experimentally and analyzed theoretically. The buckling depends weakly on Poisson's ratio and essentially is a function of the reduced prestrain, ε¯₀ =ε₀a²/h², where ε₀ is the physical prestrain, a is the width, and h is the thickness of the membrane. As ε¯₀ becomes increasingly negative, the membrane undergoes two symmetry breaking buckling transitions. Beyond the first transition occurring at ε¯_cr1, the buckling profile has all the reflection and rotation symmetries of a square. The reflection symmetries are lost through a second instability transition at ε¯_cr2. The bifurcation points, ε¯_cr1 and ε¯_cr2, and buckling profiles were calculated using analytical energy minimization and nonlinear finite-element simulation. Both methods agree. The buckling of micromachined plasma-enhanced chemical vapor deposition silicon nitride membranes on a silicon wafer is interpreted in terms of the theoretical results. Good matching between measured and calculated buckling profiles is found. The extracted strain values are consistent irrespective of the size and buckling mode of the membranes. From the average strain across the wafer ε₀=-3.50×10^-4 and complementary wafer curvature measurements, a Young's modulus of 130 GPa is deduced. Methods for the straightforward extraction of ε₀ from experimental center deflections of buckled square membranes are described     

Mobile Sensoren für die Biotechnologie – Ortsunabhängige,miniaturisierte Prozessmessung

Due to the wide variety of reactor forms in the field of biotechnology, conventional rod probes do not provide sufficiently representative measurement results. In this publication novel mobile spherical sensor units with a total diameter of 7.9 mm are presented. Based on simulations, these were optimized in their density for the best distribution in the aqueous medium. Furthermore, it was determined how different stirring speeds in typical bioreactors affect the distribution of the probes. The applicability of the probes is shown by means of three bioreactor types.     

Selective Iron‐Catalyzed Oxidation of Benzylic and Allylic Alcohols

A convenient and selective oxidation of alcohols with hydrogen peroxide to give aldehydes and ketones has been developed. Using in situ generated iron chloride complexes [Fe( L3 )₂Cl_n] [n=0–1, L3 =6‐(N‐phenylbenzimidazoyl)‐2‐pyridinecarboxylic acid], aldehydes and ketones were obtained in good yield and excellent selectivity after a short reaction time at room temperature.     

Machine learning model to predict welding quality using air-coupled acoustic emission and weld inputs

Journal of Intelligent Manufacturing - Weld evaluation processes are usually conducted in the post-weld stage. In this way, defects are found after the weld is completed, often resulting in...