Polytechnic University of Turin

About: Polytechnic University of Turin is a education organization based out in Turin, Piemonte, Italy. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 11553 authors who have published 41395 publications receiving 789320 citations. The organization is also known as: POLITO & Politecnico di Torino.

Size effects on nominal tensile strength of concrete structures: multifractality of material ligaments and dimensional transition from order to disorder

Abstract: The nominal tensile strength of concrete structures is constant for relatively large sizes, whereas it decreases with the size for relatively small sizes. When, as usually occurs, the experimental investigation does not exceed one order of magnitude in the scale range, a unique tangential slope in the bilogarithmic strength versus size diagram is found. On the other hand, when the scale range extends over more than one order of magnitude, a continuous transition from slope −1/2 to zero slope may appear. This means that for smaller scales a self-similar distribution of Griffith cracks is prevalent, whereas for larger scales the disorder is not visible, the size of the defects and heterogeneities being limited. In practice there may be a dimensional transition from disorder to order. The assumption of multifractality for the damaged material microstructure represents the basis for the so-called multifractal scaling law. This is a best-fit method that imposes the concavity of the bilogarithmic curve upwards, in contrast to the size effect law of Bažant. The relevant results in the literature for ranges in scale extending over more than one order of magnitude are analysed.

Cusp catastrophe interpretation of fracture instability

Abstract: A cohesive crack model is applied to analyse slow crack growth in elastic-softening materials. The shape of the structural load-displacement response is changed substantially by varying the size-scale while keeping the geometrical shape of the structure unchanged. The softening branch becomes steeper when the sizescale increases. A critical size-scale exists for which the softening slope is infinite. In such a case the load carrying capacity drastically decreases for relatively small displacement increments. Then, for size-scales larger than the critical one, the softening slope becomes positive and part of the load-displacement path becomes virtual if the loading process is displacement-controlled. In such a case, the loading capacity will present a discontinuity with a negative jump. The size-scale transition from ductile to brittle behaviour is governed by a nondimensional brittleness number SE which is a function of material properties and structure size-scale. A truly brittle failure occurs only with relatively low fracture toughnesses G ic, high tensile strengths σu, and/or large structure size-scales b, i.e. when S E = G ic σ u b → 0. On the other hand, if the loading process is controlled by a monotonically increasing function of time (e.g. the crack mouth opening displacement), the snap-back instability in the load-displacement curve can be captured experimentally. When the post-peak behaviour is kept under control up to the complete structure separation, the area delimited by the load-displacement curve and the displacement-axis represents the product of G ic and the initial ligament area. Finally, it is verified that. for SE → 0, the maximum load for catastrophic failure is provided by the simple LEFM condition : K 1 = K IC = G ic E (plane stress), and that there is no slow crack growth prior to instability.

The safety critical electric machines and drives in the more electric aircraft: A survey

Abstract: In order to improve aircraft efficiency, reliability and maintainability, the aerospace world has found in the progressive electrification of on-board services the way to reduce or to remove the presence of the hydraulic, mechanical and the bleed air/pneumatic systems. This concept is called More Electric Aircraft (MEA), which involves the introduction of the Electromechanical actuators (EMAs) and the electro-hydraulics actuators (EHAs) for the actuation of the flight surfaces of wide-body aircraft, moving from the “fly-by wire” to the “power-by wire” concept. The resulting step change in aircraft electrical loading will have far reaching implications for the electrical generation system. Considerable effort is being directed towards realizing the so-called More Electric Engine (MEE), which foresee an integration of the electrical generator directly inside the main gas turbine engine. Also the entire electrical distribution system is subject to radical revisiting, with a trend which is leaving the constant frequency AC energy distribution in favor of variable frequency or DC solutions. Hence, it is evident the MEA trend increments the technical challenges and research topics for the electrical engineering in the aeronautic applications. The aim of the paper is the presentation, from the electrical engineering point of view, of some of the most challenging application of electric machines and drives in the incoming new aircraft generation. There are too many on board electric components and systems to be analyzed: the authors centre the attention on the most safety critical drives: flight surface actuators, fuel pumps and generators.