Самоконтроль артериального давления, некоторые методические аспекты

давлениегипертензи

FAILURE MODE SHIFTS IN FATIGUE OF SANDWICH BEAMS

SUMMARY Sandwich beams are designed and tested in fatigue, and it is found that for high load and small number of cycles to failure, the beams fail by face tensile fracture. For lower loads, and large number of cycles to failure, the beams fail by core shear

Fatigue crack initiation and propagation in sandwich structures

The focus throughout this thesis is on the fatigue characteristics of core materials used insandwich structures. Three sandwich configurations are investigated, two with cellular foamsand one with honeycomb core material These corresponds to typical materials and dimensionsused in the marine and aeronautical industry.A modified four-point bending rig, which enables reversed loading, is successfully used forconstant amplitude fatigue tests of all material configurations. The core materials are tested asused in composite sandwich beams and through the design of the specimens the desiredfailure is in shear of the core. Analyses and inspections during and after the tests supports thetheory that the fracture initiation and fatigue failure occurs in a large zone of the core withwell distributed micro cracks rather than a single propagating crack. The fatigue test resultsare plotted in stress life diagrams including a Weibull type function which provides a goodaccuracy curve fit to the results. The fatigue life of the core materials is found to be reducedwith a increased load ratio, R.The influence on the strength and fatigue performance on sandwich beams with two types ofcore damages, an interfacial disbond and a flawed butt-joint, are experimentally investigated.The fatigue failure initiates at the stress intensity locations which are present due to the predamage.The specimens with flawed butt-joints display a fatigue crack propagation in theinterface between the core and face of the sandwich while the crack propagates through thethickness of the beams where an initial interface flaw is present. A fatigue failure predictionmodel is suggested which utilises the fatigue performance of undamaged beams and thestrength reduction due to the damages. The approach is correlated with results from fatiguetesting and satisfactory correlation is found.A uni-axial fatigue tests method is developed which simplifies the rig and specimenscompared to the four point bend method. A comparison between the results from uni-axialtension/compression fatigue tests and shear fatigue tests shows good correlation, although theR-dependency differs in some cases.The fatigue crack propagation rates are investigated for two configurations: crackspropagating in pure foam core material and cracks propagating in the core material near andalong a sandwich face/core interface. The rate at which a crack propagates stable in the socalled Paris’ regime is extracted for both Mode I and Mode II loading. The agreement betweenthe Mode I crack propagation rate in the pure foam and in the core/face sandwich interfacelayer supports the theory that the crack actually propagates in the sandwich core beneath astiffened resin rich layer present in the face/core interface. The stress intensity thresholds andthe limits at which the crack growth becomes unstable are further established.Acoustic Emission (AE) is used to monitor crack initiation and growth in the core, duringboth static and fatigue loading. It is found that the approximate location of AE-hits can bedetermined which demonstrates that AE has a potential both as an non destructive testing tooland to study the failure process of non-visible sub-surface damages in sandwich structures.QC 2010052

Fatigue crack initiation and propagation in sandwich structures

The focus throughout this thesis is on the fatigue characteristics of core materials used insandwich structures. Three sandwich configurations are investigated, two with cellular foamsand one with honeycomb core material These corresponds to typical materials and dimensionsused in the marine and aeronautical industry.A modified four-point bending rig, which enables reversed loading, is successfully used forconstant amplitude fatigue tests of all material configurations. The core materials are tested asused in composite sandwich beams and through the design of the specimens the desiredfailure is in shear of the core. Analyses and inspections during and after the tests supports thetheory that the fracture initiation and fatigue failure occurs in a large zone of the core withwell distributed micro cracks rather than a single propagating crack. The fatigue test resultsare plotted in stress life diagrams including a Weibull type function which provides a goodaccuracy curve fit to the results. The fatigue life of the core materials is found to be reducedwith a increased load ratio, R.The influence on the strength and fatigue performance on sandwich beams with two types ofcore damages, an interfacial disbond and a flawed butt-joint, are experimentally investigated.The fatigue failure initiates at the stress intensity locations which are present due to the predamage.The specimens with flawed butt-joints display a fatigue crack propagation in theinterface between the core and face of the sandwich while the crack propagates through thethickness of the beams where an initial interface flaw is present. A fatigue failure predictionmodel is suggested which utilises the fatigue performance of undamaged beams and thestrength reduction due to the damages. The approach is correlated with results from fatiguetesting and satisfactory correlation is found.A uni-axial fatigue tests method is developed which simplifies the rig and specimenscompared to the four point bend method. A comparison between the results from uni-axialtension/compression fatigue tests and shear fatigue tests shows good correlation, although theR-dependency differs in some cases.The fatigue crack propagation rates are investigated for two configurations: crackspropagating in pure foam core material and cracks propagating in the core material near andalong a sandwich face/core interface. The rate at which a crack propagates stable in the socalled Paris’ regime is extracted for both Mode I and Mode II loading. The agreement betweenthe Mode I crack propagation rate in the pure foam and in the core/face sandwich interfacelayer supports the theory that the crack actually propagates in the sandwich core beneath astiffened resin rich layer present in the face/core interface. The stress intensity thresholds andthe limits at which the crack growth becomes unstable are further established.Acoustic Emission (AE) is used to monitor crack initiation and growth in the core, duringboth static and fatigue loading. It is found that the approximate location of AE-hits can bedetermined which demonstrates that AE has a potential both as an non destructive testing tooland to study the failure process of non-visible sub-surface damages in sandwich structures.QC 2010052

Tension, compression and shear fatigue of a closed cell foam

A closed cell foam of Polymetacrylimide (Rohacell) with three different densities is studied. The foam is tested quasistatically in tension, compression and shear. The tensile properties scale very well with the relative density of the foam, but the compression and shear properties do not. It is believed to be due to cell edge and cell wall buckling being the dominated deformation mechanism in compression and shear for lower densities that does not occur for higher densities. Fatigue testing is then performed in tension, compression and shear. It is seen that for all load cases and densities, the fatigue life can be plotted using Basquin's law. The results also show that the different failure mechanisms found in the static tests are the same in fatigue. This means that the fatigue life for different load types exhibit different failure mechanisms. This shows not only as a clear difference in the stress levels for fatigue failure, but also on the slope in the fatigue life relation.QC 20141103</p

Fatigue of closed-cell foams in compression

This article deals with fatigue of closed-cell foams under compression loading. Testing is performed on three densities of Divinycell H-grade and three densities of Rohacell WF-grade foam under cyclic compression loading. The fatigue failure is in all cases described as localized crushing of cell layers. The two main observations from this are that the slopes of the stress-life curves are almost all different, both between the foam types and relative density. Secondly, the stress-life relation slopes are considerably flatter than corresponding data in tension. For one particular foam grade, the stress-life relation is almost flat.QC 20110815</p

Failure Mode Shifts in Fatigue of Sandwich Beams

Sandwich beams are designed and tested in fatigue, and it is found that for high load and small number of cycles to failure, the beams fail by face tensile fracture. For lower loads, and large number of cycles to failure, the beams fail by core shear.QC 20120119</p

Failure Mode Shifts in Fatigue of Sandwich Beams

Sandwich beams are designed and tested in fatigue, and it is found that for high load and small number of cycles to failure, the beams fail by face tensile fracture. For lower loads, and large number of cycles to failure, the beams fail by core shear.QC 20120119</p

Projekt Lister : Överhalning av en hjälpmaskin

ABSTRAKT Det här är en sammanfattning av den formella delen av vårt projektarbete. Under hösten 2007 och våren 2008 har vi på uppdrag av Egon Nilsson överhalat en hjälpmaskin ombord på Calmare Nyckel. Maskinen var i stort behov av en renovering, det läckte både kylvatten och smörjolja på olika ställen. Det har varit mycket väntetid på reservdelar eftersom maskinen är ovanlig och tillverkas i England. Mot slutet av arbetet råkade vi på bekymmer med vattenläckage i smörjoljan som gjorde att jobbet blev försenat några veckor. Läckaget lagades och maskinen provkördes. Resultatet blev bra, maskinen fungerade och gick som den skulle. Under arbetets gång har vi försökt i möjligaste mån följa de instruktioner som finns i instruktionsboken. När man genomför ett projektarbete av den här typen, skall all dokumentation rörande projektet redovisas. Materialet som presenteras i den här sammanställningen är upplagt enligt följande. Inledning till ämnet och projektet vilket följs av avsnitten projektprocessen och resultat. Till denna dokumentation har vi bifogat, arbetsdagbok och offert.ABSTRACT This is a summary of the formal part of our project. During the autumn of 2007 and spring 2008 we have done an overhaul on one of the auxiliary engines onboard Calmare Nyckel. The assignment was given from Egon Nilson. The engine was in bad shape, lubrication oil and coolingwater was leaking from several cylinders and thereby in big need of a service. There have been some waiting time during the order of new parts because of the rare engine type which are British and therefore all the parts had to be ordered from England. At the end of the project we discovered some difficulties with coolingwater leaking in to the oil sump, this causing further delays finishing the project. The problem were solved and at the test run the engine run satisfactory. During the project we have as far as possible followed the manual and other instructions available. During a project like this it is important that all documentation of the project is shown. The materials that are shown are presented with an introduction followed by the process and the result. To this documentation we have attached a working diary and quotations