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Thermo-mechanics

Explore three types of thermo-mechanics coupling, variables, material properties, and boundary conditions. Learn thermal problem solving in Abaqus and implementation of coupled thermo-mechanics.

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Thermo-mechanics

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  1. Thermo-mechanics J. Cugnoni, LMAF / EPFL 2009

  2. Three kind of « thermo-mechanics » • Un-coupled: Known temperature field => mechanical model (linear statics + th. expansion) • One way coupling: solve thermal problem => temperature field => solve mechanical problem • Fully coupled: solve at the same time temperature & displacement field (includes mechanical dissipation)

  3. Thermal problem q • Variables • Essential variable: Temperature field T • Natural variable: heat flux q • Material • Conductivity l • Density r & specific heat cp if transient • Boundary conditions: • Temperature: Tsurf = f(t) if transient • Surface heat fluxes: • Imposed heat flux qsurf=f(t) • Convection: qsurf = h (T –Text(t)) • Volume heat source: s = f(t) T, l, r, cp, s Text

  4. Thermal problem in Abaqus • Select Step = Heat transfer • Choose steady state or transient • If transient: set time period, set small initial increment, set max DT per increment (<1/10 of max DT) • In Mesh: • select element type: Heat transfer, linear • Loading: • Need to impose at least one temp. (rigid body) • Adiabatic interface: leave free = no flux! • Flux = load, Temperature = BC • Convection: in interaction module, create Surface Film condition, enter h and Text • If transient: define an amplitude curve (tool => amplitude), need to start at zero for t=0,

  5. Coupled Thermo mechanics in Abaqus • Select Step = Coupled Temp-Displacement • Choose steady state or transient • If transient: set time period, set small initial increment, set max DT per increment (<1/10 of max DT) • In Mesh: • select element type: Coupled Temp.-Displacement, quadratic • Loading: • Need to impose at least one temp. & block 6 rigid body motions • Adiabatic interface: leave free = no flux! • Flux = load, Temperature = BC • Convection: in interaction module, create Surface Film condition, enter h and Text • If transient: define an amplitude curve (tool => amplitude), need to start at zero for t=0

  6. Démos • Bi-material beam: Thermal switch • Coupled Thermo-mechanical problem • Transient analysis • Heat transfer & expansion properties • Heat transfer BC: • Temperature • Convection • Heat Flux • Time dependent boundary conditions

  7. Demo: thermal switch Beam dimensions 60 x 5 x 1 mm Invar, 0.5 mm Block: clamped, T= 0°C Convection: q=h (T-Text), h = 100 W/m2/K Water Steel, 0.5 mm T water = f(time) T=100°C T=0°C Time (s) 1 60

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