This paper considers a computation method in failure analysis of layered composites containing pin-loaded holes. The investigation is focused on developing a reliable computation procedure to analyze initial failure load for pin-loaded holes at layered composite structures. Finite element method (FEM) is used to determine stress distribution around the fastener hole. Combining Chang-Scott-Springer characteristic curve model and Tsai-Wu initial failure criterion are used to determine joint failure. Special attention in this work is paid to pin-load distributions and its effect on the load level of failure and its location. In previous work initial failure analysis was carried out using cosine distribution between pin/lug mechanically fastened joint. Here contact finite element pin/lug model is analysed. The influence of stacking sequences of layered composites containing pin-loaded holes is also investigated. Special attention is paid to failure load and mode analyses in composites with stacking sequence [0/(±45) 3 /90 3 ] S. The computation results are compared with available experimental results. Good correlations between computation and experimental results are obtained.
This paper considers the determination of the crack growth trajectory and residual life for the two-dimensional structural elements under mixed modes. To study crack growth behaviour, a specimen with two holes and a crack between them is considered. This crack is defined as achieving a mixed-mode I/II crack growth trajectory. To produce a crack growth trajectory under cyclic loads with an initial crack between the two holes, MTS servo-hydraulic system is used. Crack growth trajectory is defined using numerical simulations via finite elements. The results of the numerical simulations by finite elements are compared with experimental results. Residual life along the 'curve' mixed-mode crack growth trajectory is determined numerically and experimentally. The crack growth trajectory obtained via the presented numerical simulation and residual life are compared with own experimental results.
Original scientific paper Assessment of airfoil aerodynamic characteristics is essential part of any optimal airfoil design procedure. This paper illustrates rapid and efficient method for determination of aerodynamic characteristics of an airfoil, which is based on viscous-inviscid interaction. Inviscid flow is solved by conformal mapping, while viscous effects are determined by solving integral boundary layer equations. Displacement thickness is iteratively added to the airfoil contour by alternating inviscid and viscous solutions. With this approach efficient method is developed for airfoil design by shape perturbations. The procedure is implemented in computer code, and calculation results are compared with results of XFOIL calculations and with experiment. Eppler E387 low Reynolds number airfoil and soft stall S8036 airfoil are used for verification of developed procedure for Reynolds numbers 200000, 350000, and 500000. Calculated drag polars are presented in this paper and good agreement with experiment is achieved as long as small separation is maintained. Calculated positions of laminar separation, reattachment, and turbulent separation closely follow experimental measurement. The calculations are performed in relatively short time, which makes this approach suitable for low Reynolds number airfoil design. Keywords: airfoil design; boundary layer features; computational aerodynamics, conformal mapping; laminar separation bubble; low Reynolds number Aerodinamičke karakteristike aeroprofila za niske Rejnoldsove brojeveIzvorni znanstveni članak Procjena aerodinamičkih karakteristika aeroprofila je suštinski dio bilo kakve optimalne konstrukcije aeroprofila. Ovaj rad ilustrira brzu i efikasnu metodu za određivanje aerodinamičkih karakteristika aeroprofila, a utemeljena je na viskozno-neviskoznoj interakciji. Neviskozno strujanje je riješeno konfornim preslikavanjem, dok je doprinos viskoznih efekata određen rješavanjem jednadžbi graničnog sloja u integralnom obliku. Debljina istiskivanja graničnog sloja je iterativno dodavana konturi aeroprofila smjenjivanjem neviskoznog i viskoznog proračuna. Time je ostvaren efikasna metoda za konstruiranje aeroprofila variranjem njegovog oblika. Procedura je primijenjena u obliku računarskog programa, a rezultati proračuna su uspoređeni s rezultatima XFOIL programa i s eksperimentima. Eplerov aeroprofil za niske Rejnoldsove brojeve, E387, i aeroprofil S8036 s blagom stoling karakteristikom su primijenjeni za verifikaciju proračuna za Rejnoldsove brojeve 200000, 350000 i 500000. U radu su prikazane izračunate polare koje se dobro slažu s eksperimentima dokle god su otcjepljenja strujanja mala. Izračunati položaji mjesta laminarnog otcepljenja, pripajanja i turbulentnog otcjepljenja blisko prate eksperimentalne rezultate. Proračun se odvija relativno brzo što mu omogućava primjenu za konstrukciju aeroprofila pomoću variranja njegovog oblika.
An introductory study of helicopter main rotor blade aerodynamic shape optimization problem is presented. Optimization process is carried out in compressible, viscous, quasi-steady fluid flow field of hovering rotor described by thin layer Navier-Stokes equations. Since the gradient-based optimization technique is chosen the discrete adjoint equation method is used for gradient calculations. The airfoils in the blade cross-sections are parameterized with Non-Uniform Rational B-Splines (NURBS). Inverse three dimensional blade shape optimization example is given to demonstrate the efficiency of the numerical procedure.
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