Papers by Keyword: Plate

Abstract: In the practice of civil engineering, the methods of impact diagnostics of materials find their application, allowing quickly and accurately measure the required strength characteristics at any point in the structure. Impact methods offer many advantages, for example, at smaller dimensions can be developed big the contact force, it can be recorded more information about the response of the material to dynamic impact and others. This approach is widely used in determining the hardness of materials and makes it possible to determine the complex mechanical characteristics: yield strength, ultimate strength, and elongation. In the paper we consider the axisymmetric problem of the impact of the conical indenter on the plate, laying on Winkler Foundation under elastic-plastic deformation. The solution is based on the phenomenological model of elastic-plastic indentation in a quasistatic formulation. The general deformations of the plate are considered elastic, and the local, in the contact zone, are elastoplastic. The main characteristics of the impact are determined: the force of the contact interaction, the local indentation, the contact time. The device and methods of determining the strength characteristics of plates under specified conditions of impact were developed on the basis of obtained solutions. The proposed method has been tested on many building structures: bridges, trusses, structural structures of artificial structures, reinforcement bars, welded joints.

Abstract: In this article, nonlinear analysis of the composite plates and shells were carried out using the semiloof shell element. The finite element formulation is based on Green strains and Piola-Kirchhoff stresses. The nonlinear solution procedure was implemented to study the nonlinear behaviour of composite plates and shells. Due to coupling effect in composite plate and shells under in-plane load, pre-buckling displacement is significant and hence the behaviour is nonlinear. A verification study has been carried out to establish the efficiency of the present model. Since the margin of factor of safety is less in aerospace application, the detailed understanding and study of pre-buckling displacement is necessary for the designer.

Abstract: Structural health monitoring (SHM) is an inevitable component of modern civil and aerospace structures. It essentially detects the damages in the system by evaluating the performance parameters by the integration of sensing and possibly also actuation devices into the structure. In this paper damage detection process in an aluminium cantilever plate using piezoelectric sensors and actuators is simulated. Possible root damage such as transverse crack and longitudinal crack are studied. The results are compared with undamaged case. The plate is actuated using PZT actuators and performance is evaluated using PVDF sensors. Modelling for PZT/PVDF and structural parts are carried out using coupled field finite element PLANE223 ofAnsys^(TM) finite element package. Strain response at the root of the cantilever plate is captured as the voltage output of the PVDF sensor. Strain response is directly related to the voltage generated in the PVDF sensor. The percentage variation of the fundamental frequency is found to be less than 3% in the present study and hence it is not taken as an index of damage. The transient voltage response captured with the transient coupled field analysis shows variation up to 24% as a signature between damaged and undamaged systems. Therefore, the present study suggests transient response evaluation using PVDF sensor is a suitable evaluation technique for the cases under consideration.

Abstract: Extensive efforts are underway worldwide to develop new steels with substantial fractions of retained austenite, for lightweight automobile manufacturing and other applications requiring improved combinations of strength and formability. It is likely that microalloying can provide product enhancements in these emerging products, such as Q&P, TBF, medium-Mn TRIP, etc. and this paper examines the expected behavior of niobium using inferences based on published AHSS literature and principles of Nb microalloying. Some benefits of Nb in terms of microstructure refinement and precipitation strengthening have been reported. The potential influences of Nb are complex due to the sensitivity of Nb dissolution and precipitation to chemical composition and processing; differences in the expected role of Nb are pointed out with respect to different product forms produced via hot-rolling or annealing after cold-rolling, and microstructures with or without substantial quantities of primary ferrite. Some issues that warrant further examination are identified, as a deep understanding of Nb microalloying and other fundamental behaviors will be needed to optimize the performance of these next-generation steels.

Abstract: This paper focuses upon zigzag-shape bending for suppression of defects, including dent and springback. A series of finite element analyses was carried out in order to optimize the bending condition for suppression of these defects. As a result, it was clarified that a diagonal movement of the upper die was effective for suppression of dents while a rather vertical movement of the upper die was effective for suppression of springback. In order to suppress dent and springback at the same time, this paper proposes another method of bending method, whereby the upper die with special shape moves in a diagonal way. Moreover, the stability of the method against variation of tool dead position, which would be caused by elastic deformation of supporting members, was studied by FEM, followed by experimental verification.

Abstract: This paper presents a 2.5D moving iso-surface threshold (MIST) approach for findingtopological configurations of stiffeners for stiffened and sandwiched plates subjected to staticbending load. In this 2.5D MIST approach, (a) 3D elements are used to discretize a continuum intomulti-layered finite element model with either one or two surface layers of elements as non-designdomain; (b) the 3D non-surface elements, collocated in the thickness direction, are grouped togetherand used to define one amalgamated physical response function for each series of elements in a 2Ddesign domain; (c) optimum designs on the layout of stiffeners attached to a panel or sandwichedbetween two panels are obtained using MIST from the grouped 3D elements. Several numericalexamples are presented to demonstrate the effectiveness of the proposed approach in designingpractical stiffener topology. By using representative volume element and repetitive boundaryconditions as well as loading combinations, designs of stiffener are obtained for selected stiffenedand sandwiched plates under chosen static loading.

Abstract: Ipsilateral proximal femur combined with diaphyseal fracture is a rare and problematic combination of injuries with serious potential complications first reported in the literature by Delaney and Street in 1953. This paper offers a retrospective view of 21 cases involving ipsilateral, proximal and diaphyseal fractures in elderly patients who were treated in our department, in order to emphasize the challenges of managing these pathological entities in elderly patients and the need for improvement of implant design. A number of 21 patients treated in our department, over a five year period for ipsilateral, combined proximal (intertrochanteric or femoral neck fractures) and femoral shaft fractures was selected. The cases were the result of various types of trauma as follows: 8 patients injured in motor vehicle accidents, 11 falls from standing position and 2 falls from more than own height. No open fractures or pathological fractures were recorded for this study. The patients were grouped according to treatment approach as group A (n=13), managed using intramedullary fixation devices and group B (n=8), treated with plating. All 21 patients were followed-up for 1 to 2 years after surgery. The data was analysed using Student's t-test and a comparison between the two groups was devised. None of the available fixation methods has shown clear superiority for addressing this fracture association. The multitude of variables affecting the management of this injury pattern is complemented by the poor local biomechanical environment provided by the low bone mineral density characteristic for the elderly patients. This raises the challenge of improving the design of the implants to better suit the biomechanical requirements, which sometimes are dictated by the age of the patients.

Abstract: Distal comminuted tibial fracture with or without intra-articular involvement is a very common injury of the lower limb, especially in younger patients due to high energy trauma. The anatomical and biomechanical properties of this segment of tibia, makes this pathology a major surgical challenge with a preserved clinical outcome. The aim of this study is to present different outcome of tibial fracture, treated with open reduction and internal fixation (ORIF) with titanium angle locking plates (ALP) and to underline the physiological and non-physiological bone healing effects on implants. In this study we included 48 patients with tibial pilon fracture who underwent to ORIF, applying ALP in the Orthopedics and Trauma department of the University Emergency Hospital in Bucharest. Due to preserved biomechanical properties of ALP and this anatomical region, weight bearing is not allowed till 6 to 8 weeks. Comminuted fracture of this part of tibia often have de-vascularized bony fragments which leads to delayed union or non-union. These complications often lead to implant failure, improper bone healing or non-union. Internal fixation with angle stable screws, offers a good stability of reduction in the early postoperative period. Titanium angle locking plates offers good anatomical reduction and stable fixation in the early period of healing process. Due to its rigid, fixed position of the screws in the plates, bone remodelling during healing process and early weight bearing, increases the mechanical failure of implant.Keywords: tibial pilon fractures, angle locking plates, implant failure.

Abstract: The paper deals with experimental estimation of the frequencies of free vibrations for composite plates with damage. Two different glass-epoxy composite plates with damage were tested and their mechanical behavior was compared with their non-damaged counterparts. Dynamical properties of the tested structures were examined with the Laser Scanning Vibrometer. Finite Element Analysis (FEA) was performed simultaneously for free vibration frequencies and mode shapes. The numerical results agreed well with the experiment.

Abstract: The Ritz method is used for the buckling analysis of stiffened plates under compressive load. Suggested approximations of displacements allow taking into account the features of system wave formation. The results are compared with data, received by finite element method.