Search results for "Structural Engineering"
showing 10 items of 1998 documents
Numerical analysis of a piezoelectric structural health monitoring system for composite flange-skin delamination detection
2013
Abstract In this paper, a piezoelectric based Structural Health Monitoring (SHM) system is proposed to detect skin/stiffener debonding and delamination cracks proper of laminated composite structures. The SHM system is analyzed by means of a boundary element code implemented in the framework of piezoelectricity. The multidomain technique, coupled with an interface spring model, is used to model laminated composite structures as well as the bonding between the host delaminated structure and the piezoelectric sensor. Static sensitivity analyses are firstly performed on a drop-ply delaminated structure in order to identify a suitable configuration for the sensor. Then, the dynamic electromecha…
A simple interpretation of the effect of the polymer type on the properties of PMBs for road paving applications
2018
Abstract The paper presents the results of the rheological characterisation of polymer-modified bitumen for paving applications. In order to find a simple interpretation of the influence of polymer type on the blends produced, in this study high density and low density polyethylene (PE) with different chemical properties were used, as well as ethylene-vinyl acetate. The chemical characteristics of the base bitumen and the polymers used were determined by means of SARA analysis and Fourier Transform Infrared Spectroscopy, FTIR, respectively. The morphology of the produced blends was investigated by means of fluorescent light optic microscopy, while the mechanical properties were investigated…
Robustness of Empirical Vibration Correlation Techniques for Predicting the Instability of Unstiffened Cylindrical Composite Shells in Axial Compress…
2020
Thin-walled carbon fiber reinforced plastic (CFRP) shells are increasingly used in aerospace industry. Such shells are prone to the loss of stability under compressive loads. Furthermore, the instability onset of monocoque shells exhibits a pronounced imperfection sensitivity. The vibration correlation technique (VCT) is being developed as a nondestructive test method for evaluation of the buckling load of the shells. In this study, accuracy and robustness of an existing and a modified VCT method are evaluated. With this aim, more than 20 thin-walled unstiffened CFRP shells have been produced and tested. The results obtained suggest that the vibration response under loads exceeding 0.25 of …
Longitudinal Flexure as a Method for Determining the Flexural Strength of Composite Materials
2004
A method is presented for determining the flexural strength of composites from tests on pinned specimens in axial compression. This scheme is close to the so-called Euler buckling model, but the load is applied eccentrically, and the bar is bent practically from the beginning of loading. An analytical model is proposed for calculating the flexural stress in longitudinal flexure of a thin bar in the case of large displacements. The problem is solved in elliptic integrals of the first and second kinds. The analytical model shows an excellent agreement with experiments. The results obtained are compared with experimental tension data. A device is also designed for testing composite bars in lon…
AN ACCURATE METHOD TO PREDICT THE STRESS CONCENTRATION IN COMPOSITE LAMINATES WITH A CIRCULAR HOLE UNDER TENSILE LOADING
2007
The paper presents a theoretical-numerical hybrid method for determining the stresses distribution in composite laminates containing a circular hole and subjected to uniaxial tensile loading. The method is based upon an appropriate corrective function allowing a simple and rapid evaluation of stress distributions in a generic plate of finite width with a hole based on the theoretical stresses distribution in an infinite plate with the same hole geometry and material. In order to verify the accuracy of the method proposed, various numerical and experimental tests have been performed by considering different laminate lay-ups; in particular, the experimental results have shown that a combined …
Redesign of the Geometry of Parts Produced from PBT Composite to Improve Their Operational Behavior
2021
Parts produced from PBT-GF30 (70% polybutylene terephthalate +30% fiberglass) are very often used in car construction, due to the properties of this material. The current trend is to make parts with a shape designed to be as complex as possible, to take over many functions in operation. During the research, a part that is a component of the structure of car safety systems, and that must be completely reliable in operation, was analyzed. This piece has a complex shape that involves the intersection of several walls. Thus, the research aimed at establishing the optimal radius of connection between the walls (R), the ratio between the thickness of the intersecting walls (K) and the angle of in…
Coating fragmentation by branching cracks at large biaxial strain
2007
The fragmentation behaviour of a thin brittle coating attached to a ductile substrate subjected to equibiaxial quasi-static in-plane tension is studied. The experimentally observed cracking patterns are related to repetitively branching coating cracks. The fragmentation process is modelled by the rate equation approach. It is established that fragmentation by branching cracks leads to a qualitatively different fragment distribution compared to binary fragmentation. The fragmentation model is applied to identify crack branching and coating/substrate stress transfer parameters.
Energy criteria of multiaxial fatigue failure
1999
This paper contains a review of energy-based criteria of multiaxial fatigue. The criteria have been divided into three groups, depending on the kind of strain energy density per cycle which is assumed as a damage parameter. They are: (i) criteria based on elastic strain energy for high-cycle fatigue; (ii) criteria based on plastic strain energy for low-cycle fatigue; and (iii) criteria based on the sum of plastic and elastic strain energies for both low- and high-cycle fatigue. The criteria which take into account strain energy density in the critical plane seem to be the most promising. In the energy approach to multiaxial fatigue there is an important unsolved problem, i.e. the evaluation…
Thermo-mechanical analyses and ways of optimization of the helium cooled DEMO First Wall under RCC-MRx rules
2017
Abstract The EUROfusion Consortium develops a design of a fusion power demonstrator plant (DEMO) in the framework of the European “Horizon 2020” innovation and research program. One of the key components in the fusion reactor is the Breeding Blanket (BB) surrounding the plasma, ensuring tritium self-sufficiency, heat removal for conversion into electricity, and neutron shielding. Among the 4 candidates for the DEMO BB, 2 of them use helium as coolant (HCPB, HCLL), and another one (DCLL) uses helium to cool down the First Wall (FW) only. Due to uncertainties regarding the plasma Heat Flux (HF) load the DEMO BB integrated FW will have to cope with, a set of sensitive thermal and stress analys…
The Suitability of Chemically and Thermally Activated Quaternary Clays of Latvia as Raw Material for Geopolymer Binders
2013
It is now accepted that new binders are needed to replace Portland cement (PC) for enhanced environmental and durability performance. The urge to reduce emissions of carbon and the fact that PC structures having built a few decades ago are already facing disintegration problems points out the handicaps of PC binders. Research works carried out in developing of alkali-activated binders show that this new type of binder could have a huge potential to become as alternative building material. Latvian Quaternary clays were studied from the point of view of the national economy, analysing the physical properties and chemical composition of those sediments in connection with the possibilities of …