ANSYS Basic Concepts for ANSYS Structural Analysis

Contents Disciplines and Element Types Analysis Types Linear Analysis and Nonlinear Analysis Material Models Failure Criteria of Materials

Disciplines and Element Types Structural Analysis Thermal Analysis Fluid Dynamic Analysis Electric Field Analysis Magnetic Field Analysis Coupled-field Analysis

Examples Example 1: Thermal Stress Analysis Example 2: Structure-Fluid Interactions Example 3: Thermal Actuator

Element Types ANSYS elements are classified according to Discipline Dimensionality Geometry Order Example SOLID45: 3D hexahedral linear structural element PLANE67: 2D quadralateral linear coupled thermal-electric element

Analysis Types Structural Analysis Static Analysis Dynamic Analysis Static, Transient, Modal, Harmonic, Buckling, etc. Thermal Analysis Steady-state, Transient Electric Field Analysis Static, Transient, Modal, Harmonic etc. Static Analysis Dynamic Analysis Transient Analysis Modal Analysis Harmonic Response Analysis etc. Buckling Analysis

Transient Analysis Inertia forces Damping forces Elastic forces External forces

Static Analysis When dynamic effects can be neglected, a problem can be solved statically. Dynamic effects can be neglected only when the deformation velocity and acceleration are small. Two cases: Steady-state solution approximation solution for a real-world problem.

Modal Analysis Modal analysis is to analysis a structure under free vibration. The solutions typically include Vibration frequencies (or periods) Vibration modes

Harmonic Response Analysis Harmonic response analysis is to analysis a structure under periodic excitation of external forces. The solutions typically include maximum responses under various frequencies of external forces

Linear Analysis and Nonlinear Analysis

Linear Analysis Small deformation Hooke’s law appies No status or topological changes, eg., contacts Loads Responses

Nonlinear Analysis Geometric nonlinearity Material nonlinearity Status nonlineaity

Material Models Material models are mathematically represented by a set of equations called constitutive equations. The constitutive equations describe the relations between stresses and strains (or strain rates). The parameters in the constitutive equations are called material parameters. ANSYS provides many material models to be chosen from.

Elastic vs. Plastic Elastic materials (a) Nonlinear elastic Stress Strain (a) (b) (c) Elastic materials (a) Nonlinear elastic (b) Hysteresis elastic (c) Linear Elastic

Elastic vs. Plastic Plastic materials Strain Stress

Viscous vs. Nonviscous Nonvisous materials Time Stress Strain

Viscous vs. Nonviscous Visous materials Time Stress Strain

Viscous vs. Nonviscous Creeping Stress Relaxation Stress Strain Time

Homogeneous vs. Heterogeneous A material body is said to be homogeneous if it has uniform material properties everywhere in the body. Otherwise it is said to be heterogeneous. Note that, homogeneousness does not necessarily imply isotropy.

Isotropic, Anisotropic, and Othothropic Materials A material is said to be isotropic if it has the same material properties along any directions in the body. Otherwise it is said to be anisotropic. An anisotropic material is said to be orthotropic, if the planes of material symmetry are mutually orthogonal.

Isotropic, Anisotropic, and Othothropic Materials Hooke’s Law for Isotropic Material Hooke’s Law for Anisotropic Material Hooke’s Law for Orthotropic Material

Failure Criteria of Materis

Ductile vs. Brittle Ductile Material Brittle Material Stress Stress Strain Stress Strain Stress

Failure Criteria for Brittle Materials Maximum Principal Stress Failure Criteria: Fracture will occur when tensile stress is greater than ultimate tensile strength, i.e.,

Failure Criteria for Ductile Materials Tresca Failure Criteria: Yielding will occur when shear stress is greater than shear yield strength, i.e., or

Failure Criteria for Ductile Materials von Mises Failure Criteria: Yielding will occur when the von Mises stress is greater than yield strength, i.e.,