1,721,066 research outputs found
Mechanical properties of woven natural fiber reinforced composites
Full text linkEpoxy matrix composites reinforced with woven natural fiber were studied. Composites having fiber volume fraction greater than 55% were prepared by hand lay-up technique. For reinforcement, three different natural fibers were used, jute, flax and silk. The tensile and flexural properties were investigated and the influence of the orientation of fibers on the stiffness were analyzed. It was observed that the tensile and flexural strength of silk composites is almost equal to that of flax composite and 1.98 times that of jute composite. Moreover the stiffness of the silk composites isn't influenced by orientation of fibers. Morphological examinations were carried out using scanning electron microscopy (SEM). All specimens were coated with a thin layer gold alloy prior to SEM observations. A high voltage of 20 kV was used for making the micrographs. The SEM investigation was used to study the fracture surface of the tensile specimens of the composites samples. The results of this study indicate that using silk fiber as reinforcement could successfully develop a composite material in terms of high strength and stiffness to produce a bio-composites for light applications compared to conventional composites
HMGA1 and HMGA2 protein expression correlates with advanced tumour grade and lymph node metastasis in pancreatic adenocarcinoma.
No full textPiscuoglio S, Zlobec I, Pallante P, Sepe R, Esposito F, Zimmermann A, Diamantis I, Terracciano L, Fusco A & Karamitopoulou E (2012) Histopathology 60, 397-404 HMGA1 and HMGA2 protein expression correlates with advanced tumour grade and lymph node metastasis in pancreatic adenocarcinoma Aims: Pancreatic ductal adenocarcinoma follows a multistep model of progression through precursor lesions called pancreatic intraepithelial neoplasia (PanIN). The high mobility group A1 (HMGA1) and high mobility group A2 (HMGA2) proteins are architectural transcription factors that have been implicated in the pathogenesis and progression of malignant tumours, including pancreatic cancer. The aim of this study was to explore the role of HMGA1 and HMGA2 in pancreatic carcinogenesis. Methods and results: HMGA1 and HMGA2 expression was examined in 210 ductal pancreatic adenocarcinomas from resection specimens, combined on a tissue microarray also including 40 examples of PanIN and 40 normal controls. The results were correlated with the clinicopathological parameters of the tumours and the outcome of the patients. The percentage of tumour cells showing HMGA1 and HMGA2 nuclear immunoreactivity correlated positively with increasing malignancy grade and lymph node metastasis. Moreover, HMGA1 and HMGA2 expression was significantly higher in invasive carcinomas than in PanINs. No, or very low, expression was found in normal pancreatic tissue. Conclusions: Our results suggest that HMGA1 and HMGA2 are implicated in pancreatic carcinogenesis and may play a role in tumour progression towards a more malignant phenotype
Trattamenti microchirurgici delle rare compressioni radicolari da gas intrarachideo. Valutazioni diagnostiche con RMI
No full textNumerical and experimental validation of residual stresses of laser-welded joints and their influence on the fatigue behaviour
No full textIn this work laser-welded tube-tube specimens made of aluminium alloys AlMg3.5Mn and AlSi1MgMn T6 were experimentally tested under constant and variable amplitude loading, under pure axial and pure torsion loading. In order to evaluate the influence on fatigue behaviour of the residual stresses, because of the welding process, some specimens were subjected to postweld heat treatment and then were tested. The numerical analyses, using finite element (FE), were carried out to obtain a reliable estimation of the residual stress in the specimen. The numerical results were in a good agreement with experimental ones obtained by means of hole-drilling method. Finally, the residual stress distribution was superimposed to stress distribution because of fatigue loads obtained by FE analyses applying local concept, to calculate the stresses in the crack initiation zone and to understand the different types of failure that occurred in as-welded and relieved specimens
Numerical study of the structural behaviour of impacted composite laminates subjected to compression load
No full textComposite materials allow all the benefits which a high specific strength involves, in a design process their application involves many critical problems. Currently, these problems, such as environmental conditions, notch sensitivity, damaging under low velocity impacts, are taken into account by means of the application of conservative design safety factors regarding the ultimate tensile strength. In order to try to reduce these safety factors, this work aimed to study and to understand the impact damage growing mechanisms due to compression loads. To this purpose, compression tests have been experimentally performed on composite panels, which have been previously subjected to low velocity impact phenomena, considering impact energies of 6 J, 10 J and 13 J respectively. Moreover, numerical model able to simulate Low Velocity Impacts (LVI) and Compression After Impacts (CAI) onto CFRP panels is proposed. A single explicit finite element analysis has been carried out by using the Abaqus® finite element code; the need to build a numerical model, which allows simulation in only one analysis both LVI and CAI steps, depends on the difficulty to import the impact damage distribution into a separate compression analysis. In fact, in only one analysis the compression step can occur directly onto the impacted plate, which allows to consider the effective impact damage distribution as the starting configuration for quasi static analysis under operating loads
Multiaxial Fatigue Crack Propagation of an Edge Crack in a Cylindrical Specimen Undergoing Combined Tension-Torsion Loading
Full text linkAbstractA three-dimensional crack propagation simulation of a hollow cylinder undergoing coupled traction and torsion loading conditions is performed by the Dual Boundary Element Method (DBEM). The maximum tension load and torque are equal to 40 kN and 250 Nm respectively. Specimens, made of Al alloys B95AT and D16T, have been experimentally tested with in-phase constant amplitude loads. The Stress Intensity Factors (SIFs) along the front of an initial part through crack, initiated from the external surface of the hollow cylinder, are calculated by the J-integral approach. The crack path is evaluated by using the Minimum Strain Energy Density (MSED) criterion whereas the Paris’ law, calibrated for the material under analysis, is used to calculate crack growth rates. A cross comparison between DBEM and experimental results is presented, showing a good agreement in terms of crack growth rates and paths
Numerical and experimental investigation of residual strength of a LVI damaged CFRP omega stiffened panel with a cut-out
No full textThe fibre-reinforced epoxy composite materials, thanks to their high specific strength, have found many applications in the last decades, especially in the transportation field. However, even though this great advantage allows having a lightweight and strong structure, their application is limited by many critical aspects. Some of these depend on the fact that the composite materials are prone to a large range of defects and damages if subjected to some types of loads. Such defects and damages can be very critical for composites structures, because they may be invisible and cause a significant decrease of the residual strength. In these circumstances, if a structure is not designed under a damage tolerance philosophy it might fail under an unexpected load value, also because the presence of defects can promote the arising of unexpected instability phenomena, as for example buckling under compressive loads. For this reason, one of the most critical aspects to consider during a design process is the structural behaviour of a component under compression load. In fact, fibre and matrix failures and delaminations could reduce the residual strength of a structural component and decrease the buckling load limit. So, defects and damages which could be due either to a critical phenomenon that has previously affected the structure, such as a Low Velocity Impact (LVI), or due to voids and defects caused by manufacturing and production processes, have to be taken into account during the design process. In particular, among different defects and damages, which can affect a composite material, both delamination and fibre failures are the most dangerous. In order to assess the residual strength of damaged composite structures, compression tests are usually performed on such structures. For example, compressive tests are experimentally carried out on damaged structural components, which have been affected to an LVI in a previous phase. With the aim of studying and better understanding the structural behaviour of composites panel under compressive loads, some experimental tests and the respective numerical simulations, based on finite elements theory, have been performed and presented in the paper. The compressive test is numerically reproduced by using the finite element code Abaqus®, which, thanks to its implemented algorithms, has allowed considering different failure modes. Moreover, the progressive damage of fibre reinforced composites has been modelled by using Hashin's criteria which allowed considering two different laws for damage initiation and propagation. In particular, the paper deals with structural behaviour of both undamaged and damaged aircraft panels, with omega stiffeners, made of fibre-reinforced composite materials subjected to static compression tests. A comparison between the structural behaviours of both types of panels has been performed and presented in the paper. Moreover, with numerical model validation purpose, also a correlation between numerical and experimental results has been performed and shown in the paper
Tensile testing of hybrid composite joints
No full textIn the present paper, results of experimental tests carried out on hybrid (bonded/bolted) and adhesive composite single-lap joints are showed. The laminate adherends were made by unidirectional carbon fiber/epoxy with symmetric stacking sequence. In particular, the tests were carried out to evaluate strength and failure mode of the different joints. These joints were subjected to quasi-static tensile displacement and tests were conducted using a universal testing machine. The maximum tension load that the specimen can bear is determined and the failure process is correlated to the lay-up of the composite and joint type
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