ABSTRACT--The originally developed reflection method of caustics is presented for application to cracks in mechanically anisotropic materials such as fiber-reinforced composites. The derived solutions for the combination of crack-opening modes I and II show that the size of the dark spot depends on the load intensity, whereas its shape depends strongly on the mechanical properties of the material, the orientation of the crack tip and the mixed-mode mixture. The evaluation of optical effects is possible using the diameter-measuring method or the advanced multipoint overdeterministic data reduction method. To find the exact position of caustics, the experimental images are analyzed by the simple boundary value method and a more sophisticated differential method, which is accomplished by shifting the real image onto the gradient image. The standard experimental testing procedure is performed for cracks oriented 0 deg, 45 deg and 90 deg to the material axes in carbon-fiber-reinforced polymer composites.
Thermoelastic stress analysis (TSA) is one of the methods in experimental mechanics used for qualitative and quantitative estimation of the stress. state on the surface of cyclically loaded structures which can be either models or actual structures in their operating environment. In this paper critical remarks are given on two different theoretical approaches to derive the main TSA equation of isotropic materials. The main TSA equation of generally anisotropic and orthotropic materials is also shown. Furthermore, the influence of temperature on thermomechanical features of the materials is investigated. By comparing several construction and model materials it is shown that makrolon is the most suitable material for model making in the thermoelastic stress analysis.
Abstract. Regions with high stress gradients represent critical zones of engineering structures such as crack tip or vicinity of the contact zone. The optical method of caustics is one of the few experimental methods which provide applicable results in these locations. This method was originally developed for crack-tip measurements of stress intensity factors and J-integral for isotropic and then for anisotropic materials. Subsequently, it was extended to contact problems where the size and shape of caustics on the screen are related to the amount and the inclination of loading force. Here, the method of caustics is extended to the analysis of contact problems for mechanically anisotropic materials. This makes the caustics method widely applicable to the analysis of any high stress gradient locations in a structure.
Regions with high stress gradients represent critical zones of engineering structures, such as crack tip or vicinity of the contact zone. The optical method of caustics is one of the few experimental methods which provide applicable results in these locations. This method was originally developed for crack-tip measurements of stress intensity factors and J-integral for isotropic and then for anisotropic materials. Subsequently, it was extended to the contact problems, where the size and the shape of caustics are related to the amount and the inclination of loading force. Here, the application of the method of caustics is extended to the analysis of contact problems for mechanically anisotropic materials. This makes the caustics method widely applicable to the analysis of any high stress gradient locations in a structure.
Osnivanjem Tehničke visoke škole
1919. u Zagrebu pokrenuto je organizirano djelovanje i razvoj tehničkoga
visokoga školstva i znanosti u Hrvatskoj, čime je potaknut i razvoj
Zagrebačkoga sveučilišta, u sastavu kojega je niz tehničkih fakulteta,
sljednika ustrojbenih jedinica (odjela) Škole, tj. od 1926. Tehničkoga
fakulteta. Ovaj rad donosi kronološki pregled pokretanja, razvoja i djelovanja
tih dviju institucija kao nositelja suvremenoga razvoja tehnike i tehničkih
znanosti u prvoj polovici XX. st. u Hrvatskoj, njihovu organizaciju, podjelu na
zasebne ustrojbene jedinice, te istaknutih stručnjaka, profesora i doajena
hrvatske tehnike koji su nosili njihovu djelatnost do konačne diobe i prestanka
djelovanja te jedinstvene institucije tehničkoga visokoga školstva u Hrvatskoj.
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