12115

11101

كارشناسي ارشد

طراحي كاربردي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مكانيك

1395

هشت،69ص.: مصور، جدول، عكس(رنگي)، نمودار

ص. ع. به فارسي و انگليسي

مصطفي جمشيديان

سعيد ضيايي راد

واژه نامه

مهدي جوانبخت، محمد سيلاني

1395/11/17

كتابنامه

مكانيك

مهندسي مكانيك

ID11101

چكيده در اين تحقيق با استفاده از روش ميدان فـاز رشـد دانـه در يـك حجمـك نمايندۀ پليكريستالي تحت بارگـذاري االسـتيك در دو حالـت همسـانگردي و ناهمسانگردي خواص مرزدانه شبيهسـازي شـده و نتـايج ايـن دو حالـت بـا ـ يكديگر مقايسه شدهاند براي محاسبۀ انرژي مرزدانه در حالت ناهمسانگرد از رابطۀ رد شكلي استفاده شده است كه طبق اين رابطه انرژي مـرز بـه اختالف جهتگيري و شيب مرزدانه وابسـته ميباشـد شبيهسـازي بـراي حالـت ـ همسانگرد و هر دو حالت ناهمسانگردي يعني ناهمسانگردي وابسته به اختالف جهتگيري و ناهمسانگردي وابسته به شيب مرزدانه و تحت بارگذاريهاي كششي و برشي انجام شده است نتايج شبيهسازي نشان ميدهند كه در نظـر گـرفتن اثرات ناهمسانگردي وابسته به اختالف جهتگيري تـثثير قابـل تـوجهي بـر فرآيند رشد دانه در ريزساختار و تغيير خواص ماكروسكوپيك حجمك نماينده داشته كه از جمله ميتوان به كند شدن رشد دانهها مجتمع شـدن دانـههاي با جهتگيري مشابه كشيدگي دانهها و همچنين كند شـدن نـرك كـاهش پاسـ تنشي حجمك نماينده تحت بارگذاري كرنش ثابت اشاره كرد اما ناهمسانگردي وابسته به شيب مرزدانه روي شكل مرز تثثيرگذار بوده و اثرچشـمگيري روي نحوۀ كنار هم قرار گرفتن دانهها و در نتيجه خـواص ماكروسـكوپيك مـاده نخواهد داشت كلمات كليدي مرزدانۀ ناهمسانگرد ريزساختار چندبلوري نظريۀ ميدان فاز شبيهسازيهاي كامپيوتري

Phase Field Modeling of Stressed Grain Growth Considering Anisotropic Grain Boundary Properties Ehsan Shahnooshi e shahnooshi@me iut ac ir Date of Submission 2017 01 11 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Dr Mostafa Jamshidian jamshidian@cc iut ac irAbstract In this study normal grain growth and stressed grain growth are simulated in a copper polycrystalline thinfilm as a representative volume element RVE considering isotropic and anisotropic grain boundary energyproperties using phase field theory Our phase field theory is a thermodynamically consistent method forsolving interfacial problems like microstructure evolution Two main parameters are dominant in grainboundary migration grain boundary energy and grain boundary mobility These parameters are included inphase field equations using physical parameters defined in phase field model If grain boundary energy andmobility remain constant for all grain boundaries the grain boundary is called isotropic On the other hand ifthe grain boundary energy and mobility have different values for each grain boundary the grain boundary iscalled anisotropic We studied normal and stressed grain growth under shear and elongation conditions Thestress effect due to the elastic deformation is included as elastic strain energy term to the grain boundaryenergy term The loading is applied as a constant uniaxial strain by applying the deformation to an element inABAQUS and the phase field equations are solved by using a UMAT subroutine The texture and thereforethe total elastic stiffness of the RVE will be changed under loading Changing of elastic tensor causes thestress to be changed under constant strain called stress relaxation Computer simulations are performed forisotropic and anisotropic cases and the results are compared The anisotropic grain boundary energy iscalculated by Read Shockley equation which is based on the dislocation theory for low angle tilt boundaries In this equation the grain boundary energy depends on two parameters the in plane misorientation betweenthe neighbouring crystals which is the difference between the crystal orientations and the inclination of grainboundary which is the angle between the bisector of misorientation and the normal to the grain boundary According to this equation the grain boundary energy is the same as the isotropic case for high angle tiltboundaries But for low angle boundaries less than 15 the grain boundary energy is less than the isotropiccase So the anisotropic energy is generally less or equal to the isotropic case The simulations show that themisorientation dependent anisotropy has a significant influence on texture evolution and the changing ofpolycrystalline macroscopic properties For example decreasing the rate of grain growth aggregation of thegrains with similar orientations stretched grains and decelerating the rate of stress decreasing in stressrelaxation are some phenomena which have been observed These observations are due to the Read Shockleymisorientation dependent term which makes the low angle boundaries to be more resisting in the RVE Theinclination dependency means that different inclinations have different energies For example in a circularbicrystalline the circular boundary will remain circular in shrink or growth But in inclination dependentanisotropy the circular boundary will attain a square shape in shrink and a rhombus shape in growth Theresults show that inclination dependent anisotropy has no significant effect on grain growth rate and justcontrols the grain boundary shape This point causes the inclination anisotropy to have no effect onpolycrystalline texture and therefore no effect on mechanical properties Keywords Anisotropic grain boundary Polycrystalline microstructure Phase field theory Computersimulations

مصطفي جمشيديان

سعيد ضيايي راد

مهدي جوانبخت، محمد سيلاني