铝合金5052材料表征.docx

1、铝合金5052材料表征Chapter 3 Material model and material characterization of automotive aluminium alloy 5052H343.1 preface The basic property of material decides the use function of the structure.in the research of car crashes and large deformation of key components,the key point of solving the problem is t

2、o build corresponding physics-math model in order to acquire the specific material parameters.As for the automotive aluminium alloy in our research ,we need to consider the response characteristic of the material machanism on condition of real impact (such as dynamic loading,high-stress condition,in

3、cluding primary defects or damage,etc) .By this way, numerous performance test and full-size componnet crash test need to be conducted ,which would exhaust great labor power and physical resources,but the result is still dubious.With the limited discret data obtain by the experiment,it can hardly co

4、ver the space of all solution of the model.For some extreme condition such as shearing stress condtion, high strain rate(12102),it hard to predict its machanism response. Therefore,this model we built has its comparatively large limitations.But combine with numerical simulations,it can expand the sp

5、ace of the model effectively,while obtain complete material parameters. The result shows that the precision of numerical simulation is largely depend on the precision of material parameter to input. In the analysis of large deformation,mater-ial machanism must describe the material change from elast

6、ic deformation,elastoplastic deformation,damage progession,evolvement,fracture,which is multi-step machanism procedure. Besides,various strain rate,anisotropic caused by processing history,etc need to be take into account to consider its affection with constitutive relations. Previously,this is a ex

7、tremely complex project,where many problems is still unsolved. J.G.Blauel and D.Z.Su,etc simply used tensile bar experiment combined with finite element to simulate the characterization of AW6016 automotive aluminium alloy and crash test of the typical components in automobiles.It predicts the stati

8、c and dynamic response of the aluminium alloy and key components in macro perspective,and expand G-T-N model in micro perspective,which explain the ductile fracture of the aluminium and its initiation and evlovement by machanism of growth of voids,that could be applied in engneering calculations.Fra

9、nck Lauro and Bruno Bennani built dynamical loading machanism model on finite-element calculation terrace.This model take elastic flow and anisotropic of micro holes damage evolvement into account.Thereby this could be used to predict situation of damage and fracture of materials with obvious textur

10、e deformation such as extruded aluminium alloys in circumstances of dynamic loading with large deformation. The other one contribution of Franks research is to develop iterative algorithm which is a experiment combine with numerical simulation to achieve solving and correct the key parameter in mate

11、rial model.This method uses notch tensile data as the basic input,which can derive parameter of G-T-N damage model, and revise these parameters in consider of anisotropic factors.Eventually,the result of numerical simulation hit off with experiments.In compare with other material characterization me

12、thod ,this could avoid a great amount of experiment expenses,and improving the efficency of modeling rate. On the other hand,this method does not consider the changes of damage machanism of the materials under lower stress condition.The result proved that when three dimension stress degree is below

13、1,with the reducing of stress degree,shear slip failure would take the dominent position, and damage of void type will be supressed. So,to adopte single damge model would limit its applicability. This chapter is trying to conduct material characterization,acquire fracture parameter of the material u

14、nder simple tension,notch and shear stress,to carry out tensile test in condition of static,quasi-static and dynamic loading,and numerical simulation,furthermore,gain machanical property under different strain rate.Two kinds of damage model were built in this basis,compare the precision of model and

15、 sphere of application of these two,to describe the damage and fracture behaviour in large deformation from macro phenomenon an micro machanism.3.2 Research of machanical property test of material under static and dynamic loading.3.2.1 Basic introduction of the experiment1.overall thinking of the ex

16、periments. As for the automotive alminium alloy 5052H3.4,it is mainly used in weld production in bearing weight component of car-body,in actual collision design,these structure would mostly have large elastic deformation before failure.Therefore ,its not enough for material characterization only con

17、sidering to satisfy strength demand,the rheological future of material in large elastic deformation,such as work hardening,anisotropic and facture features of primary damage and evolvement,etc.While these machnical properties are tied up with inside factors such as microstruture,distribution,and out

18、side factors of working temperature,loading rate and stress condition.As for specific aluminium alloy,its organization structure is fixed,but the work temperature and loading condition varies with the actual impact process,so we need to conduct a series of sysmatical experiments on characterization

19、of this kind of aluminium alloy.Take research in machanical response under static and dynamic condition.On this sense,this is a project,which needs particular category and unify requirements.2.Basic information of specimens In accordance with the actual impact condition,we need to take static and dy

20、namic loading machanical property test in aluminium alloy 5052H43,the experiment was divided into five groups,which is smooth tensile test,notch tensile test,double notch shear test,Iosipescu shear test,dynamic tensile loading test.Serial number of the test specimens and experiment condition are sho

21、w in Table.3.1,sizes of the specimens are show in Fig.3.2,the specimens are cut from original plate by using (电火花技术),the distribution of all the specimens on plate can be seen on Fig 3.1. As for the serial number of the specimens ,taking PT1-UT-S1Q as an example for explanation:3.2.2 Static uniaxial

22、 tesnile test3.2.2.1 experiment equipment Uniaxial smooth tensile test is one of the basic machanical property test,which is mainly used to measure flow curve of material and strength index.The primary aim of this test is to measure the actual stress-strain curve and fracture parameter,in order to p

23、rovide with material property for following numerical simulation.So as to expand the scale of the test data,obtain practical data as much as possible,the experiment adopted two sets of equipments.one is the strength-displacement detect system,which uses extend-measurement displacement,also loading s

24、ensor to measure load,which is owned by Instron 1886 tensile test machine. Another set of machine is optical deformation measure system,including static camera,digital transition card and following image processing software and diagram calculation softeware.The system is equiped with two sets of dig

25、ital camera, the shooting angle is seperatively perpendicular to front side and lateral side of the specimens, distributted by 90 degrees.Therefore it could detect changes in width and thickness direction immediately when the specimen is in the tensile process,with dynamic image detecting to acquire

26、 changes in specimen section,so we could calculate the minium section size Ai ,according to the formulation in figure3.2 to calculate the actual stress ,strain in tensile process,which could get stress-strain relation of the tensile specimens after necking. Fig3.3 is the schematic chart of the exper

27、iment equipments.These two sets of equipments works collaboratively.The common stress-displcement is mainly responsible for recording of whole course loading detection and elastic deformation and partial ductile deformation(before maxmium loading),while the optical detecting system aim at recording

28、of detection of elastic and ductile(before fracture) deformation. We can see from Chaper 2.3.3 that the true strain of aluminium alloy 5052H34 is 9.6% correspond to static maxmium tensile load at room temperature,and fracture strain f is 73% at fracturing,at this time,these data segement is undetect

29、able by using ordinary tensile experiment,and there will be severe error in the coming up numerical simulation. By contrast,segment data after necking can be repaired if optical detecting system is used,and the maxmium true strain can be measured up to 56.1%.The measure problem of stress-strain curv

30、e can be fixed by linear interpolation.Comparison of Curves of specific materials and precision of numerical simulation will be discussed in this chapter in related diagrams.3.2.2.2 Discussion1 Relationships of stress-strain The true curves by two sets of different kinds of detecting system can be s

31、how in Fig3.4,we can see that the data scale of optial deformation system covered wider,while the complexity and costs of this detecting system is relatively higher.2 Material characterization of relativity of anisotropic and stress condition Specimen of smooth tensile test is cut from the direction

32、 of vertical and parallel to the rolling direction,the engineering stress-strian curves can be seen in Fig.3.5.From the result,the experiment displayed excellent repitiveness and stablity of data recording.Curves react that vertical yeild stress is 22Mpa higher than parallel yield stress,tensile str

33、ength is 26Mpa higher,which demostrates particular anisotropic.The size and distribution of grains is regular from further research in microstructure.First,grian sizes of the suface is larger than center grains (Fig.3.6). sec-ondly,there are certain grain orientation in the center of the material(Fig.3.7).Part of the grain in the axis along