Workshop 6: Computing Crack Growth with ANSYS SIFs and the Paris Law on a 2D Pressure Vessel

The objective of this workshop is to provide the groundwork for crack growth analysis. In this workshop, students solve a 2D pressure vessel study for varying crack lengths using Ansys Mechanical with a parametric model.

The workshop then provides a basis for computing crack growth information using a spreadsheet, allows the student to experiment with the crack growth computation, and asks several engineering questions:

·         What crack length causes immediate fracture?
·         Is limit load exceeded?
·         Is the curve fit for crack growth adequate for small cracks?

Workshop 7: SMART Crack Growth on Intersecting Pipes

This workshop is the first of two workshops that demonstrate the use of SMART. Students will learn how to setup an automated crack growth analysis using the Semi-Elliptical Crack combined with SMART Crack Growth object. Detailed definition of the Paris Law material constants for crack growth is also covered.

Automated crack growth has a host of new results post-processing options for Crack Extension, Equivalent Stress Intensity Range and Cycles; students will work through these options as well.

Workshop 8: SMART Crack Growth on a Casting with a Thermal Gradient

In this workshop, students learn how to create a crack using a 3D surface representation of the crack surface. This is made possible via the Arbitrary Crack feature, which allows a complex, non-planar 3D surface to be used as a basis for generating a crack mesh.

Workshop 9: SMART Crack Growth on a Casting with an Initial Stress State

This workshop is a continuation of workshop 8, where students load a casting with a thermal gradient and grow a crack. In this workshop, an initial stress state is set up that includes this thermal gradient and bolt pretension. The initial stress state is passed to a downstream analysis where the cyclic load to grow the crack is pressure. SMART crack growth is used here; Ansys automatically handles this initial stress state each time the crack calculation is performed.

Workshop 10: Adhesive Failure Modeling with Contact Debonding

This workshop demonstrates modeling failure of an adhesive layer via bonded contact. Students define a cohesive zone material model with properties for maximum normal stress and critical fracture energy. The benefit of this capability is that the adhesive layer does not need to be directly modeled. This is a huge benefit as the adhesive layer is typically much smaller in thickness compared to the parent parts bonded together. A secondary benefit is the mesh does not need to be the same on either side of the interface, as contact is used to initial tie the parent parts together.

Workshop 11: Adhesive Failure Modeling with Interface Delamination

This workshop demonstrates a second method to simulate interface failure; interface delamination. A similar material model is defined for this method. However, contact is not required for this capability. Instead, the mesh on both parent parts must be the same at the interface with the adhesive. This is accomplished through clever meshing or match mesh controls. The interface delamination capability also has another special use case: delamination modeling with composite models created in Ansys Composite PrepPost.

Workshop 2 Random Vibration Analysis of a PWB Assembly

This workshop extends workshop 1b to include random vibration and fatigue life prediction for a 2 hour shaker table test.  The student defines a random vibration PSD spectrum, solves the model, reviews standard deviation of stress (1s, 2s, and 3s) and finally evaluates fatigue life using the Steinberg method. Postprocessing also includes defining probes for response PSD and calculation of apparent frequency. The instructor will review the Steinberg calculations in a spreadsheet and confirm that the spreadsheet calculations match the Ansys results.

The workshop also shows the student how to approximate the 1s displacements with a hand calculation using the equation:

a = √ (Π/2 P fn Q)*
a = Acceleration in G
P = PSD value in G2/Hz from PSD curve at the natural frequency  of the SDOF system
fn = Natural frequency of SDOF system, Hz
Q = Transmissibility of SDOF system = 1/2x**; where x is the damping ratio.      

Workshop 3a Response Spectrum Analysis of a Telecommunication Rack Subjected to Zone 4 Seismic Load (Telcordia Specifications)

This workshop introduces the student to response spectrum analysis in Ansys. The student will first perform normal modes analysis on a telecommunications equipment rack and then define a Zone 4 response spectrum load. Zone 4 is accepted throughout the telecommunications industry as the most severe type of seismic loading, and many companies are required to pass a Zone 4 shaker table test in order to qualify their equipment. After performing the solution with the Zone 4 spectrum the student will review the maximum displacements and stresses due to the Zone 4 test.

The workshop also shows the student how to approximate the maximum rack displacements by approximating the model as a single degree of freedom spring-mass system.

Workshop 3b Response Spectrum Analysis of a PWB Assembly

This work reinforces skills the student learned in Workshop 3a. In addition the workshop guides the student through the process of making sure he uses a sufficient number of modes in the normal modes analysis to get good answers in the response spectrum analysis.

Workshop 4 Full Transient Dynamic Analysis of a Black Box Electronics Assembly Subjected to a Half Sine Shock

Many Ansys customers qualify their products by putting them on a shaker table and subjecting them to half sine shock. This workshop guides the student through a half sine shock analysis of a Black Box Electronics Assembly using the full transient Ansys solver.

The student solves the model as linear and then solves it as nonlinear by activating large deflection effects. Finally the student compares solution times and results to weigh the trade offs in modeling the structure as linear and nonlinear.

Workshop 5a  Mode Superposition Transient Analysis of a Black Box Electronics Assembly Subjected to a Half Sine Shock

In this workshop the student solves the model of workshop 4a using the mode superposition transient solver instead of the full transient solver.

The student acquires additional postprocessing skill related to transient analysis. He also solves the model using different numbers of modes to confirm that he has used a sufficient number of modes to get good transient results.

 
Workshop 5b Seismic Mode Superposition Transient and Response Spectrum Analysis of a Telecommunications Rack

The student subjects the telecommunications rack from a previous workshop to seismic loads from the famous                                    1940 earthquake of El Centro, CA. The student solves the model using the ground motion acceleration time history in a mode superposition transient analysis and then solve the same model using the corresponding response spectrum.

The student confirms that the response spectrum model stresses and displacements match the worst stresses and displacements from the transient model.

Workshop 6 Analysis of a PWB Assembly Subjected to Half Sine Shock Using Dynamic Load Factor

In this workshop the student uses the Dynamic Load Factor approach to solve the problem of a PWB assembly subjected to half sine shock. The DLF approach allows the engineer to avoid performing a transient solution. The DLF method involves doing a normal modes analysis and then finding a factor based on the ratio first mode’s period to the shock pulse time. The student then uses this ratio in a look up table to scale the results of a static model.

Workshop 7a Drop Test Simulation of a Radio Housing Assembly

This workshop involves drop test simulation of a plastic radio housing, and it reinforces the skills the student learned in Workshop 7a. A new twist is that the student will set up an initial velocity initial condition for the housing to specify the housing velocity immediately prior to impact. The initial velocity is based on the drop height.

Workshop 7b Nonlinear Transient Dynamic Analysis to Simulation PWB Bench Test

This workshop introduces the student to nonlinear transient dynamic analysis. With this model the student simulates a technician’s accidental drop of a PCB on a workshop table. The model involves solving the model initially as static to set up initial conditions.

Workshop 7c Plucking Technique to Estimate the Natural Frequency of a Propeller Roof Fan Assembly

This workshop demonstrates the technique to calculate natural frequency for a nonlinear system. This fan blade assembly has nonlinear contact, and sheet metal deflections are sufficient large that large deflection effects need to be active.

The technique is a plucking technique. The first step of the solution is to perform a static analysis with imposed nonzero displacements, i.e. the pluck. In step 2 the imposed displacements are removed and dynamic effects are activated so that the structure can vibrate freely as a nonlinear transient dynamic model. The student calculates natural frequency by measuring the time between displacement peaks as the structure vibrates.

Workshop 7d Explicit Dynamic Analysis Simulating an Oblique Projectile Impact

This workshop introduces the student to nonlinear transient dynamics using the Ansys Mechanical explicit dynamics solver. The student defines material failure criteria so that the kinetic energy project is able to make a hole through the two plates during impact.

Workshop 7e Tree Grapple Rigid Body Dynamic and Flexible Nonlinear Transient Dynamic Simulation

This workshop introduces joints and the rigid dynamics solver. The student defines joints for the tree grapple mechanism and checks the system kinematic model number of degrees of freedom using  Ansys redundancy analysis. He then runs the solution with all of the parts defined as rigid using the rigid dynamics solver. The rigid dynamics solution allows the engineer to confirm that the joints are defined properly, and it also allows the engineer to check joint forces. Finally, the student makes the boom flexible, solves the model using the flexible body nonlinear transient dynamics solver, and compares the rigid and flexible body solutions.

Workshop 7f Tree Grapple Rigid Dynamic with Component Mode Synthesis Simulation

Workshop 7f is a continuation of workshop 7e. The student returns to the rigid dynamics version of the tree grapple model and employs component mode synthesis (CMS) to the boom of the rigid dynamics model.  CMS allows flexible parts in rigid dynamics solutions. Finally the student compares the rigid dynamic with CMS solution to the flexible body nonlinear transient dynamic solution.

Workshop 8a Harmonic Response Analysis of an Engine Alternator Bracket

In this workshop we return to the first workshop of the course, the marine engine alternator bracket, in which we calculated natural frequencies and mode shapes. We shake the bracket at its attach points to the engine with harmonic base motion acceleration, and we calculate stresses and fatigue life based on dwelling at the first natural frequency.

Workshop 8b Harmonic Analysis of a Flight Simulator Tilt Base Structure

This workshops involves modeling of a fuselage flight trainer tilt base. The structure has scissor mechanisms that allow 3 degrees of freedom in a kinematic sense: vertical motion, pitch, and roll. Three hydraulic cylinders provide motion and can be used to shake the structure to simulate fight turbulence. This workshop allows the student to specify harmonic motion at the hydraulic jacks that are out of phase with one another.

Workshop 8c — Rotating Unbalance Loads on a Steel Structure

This steel structure has a machine on its deck that has a rotating unbalance load. We use a pair of harmonic loads 90 degrees out of phase with one another to simulate the rotating unbalance load. The model produces displacements and stresses as the structure vibrates due to the rotating unbalance load.

Workshop 2a – Nonlinear Contact Analysis of a Ring Gear and Housing Assembly with Interference

This model involves calculating stresses in the housing and ring gear due to initial interference. The initial interference in combination with friction holds the ring gear securely in the housing. This workshop provides additional practice on setting up, solving, and postprocessing nonlinear contact problems.

Workshop 2b – Nonlinear Contact Analysis of a Cell Phone Antenna Snap Fit 

The problem initially does not converge, and the student adjusts nonlinear model parameters to make it converge. The model then gives incorrect answers, and the student resolves that problem. The student also uses a commands object to control whether the symmetric or unsymmetric solver is used in order to improve solution performance. In this workshop the student uses a nonlinear contact solution with friction to simulate a cell phone antenna snap fit problem.   

Workshop 3a – Nonlinear Contact Analysis of a Ring Gear and Housing Assembly with Plasticity

This model involves calculating stresses in the housing and ring gear due to initial interference. This model expands upon workshop 2b and introduces plasticity to the model. Students post-process total strain to determine if the interference specification satisfies the design criteria of maximum 1% total strain.

Workshop 3b – 2D Plasticity Analysis of a Threaded Connection including Nonlinear Contact and Elastic-Plastic Behavior

This model represents a four part threaded connection assembly. Nonlinear contact is used to model interaction of the threads and the mating surfaces of the other parts. Students define a multilinear elastic-plastic model and calculate plastic and total strains.

Workshop 4a – Linear and Nonlinear Buckling Analysis of a Steel Column

This assembly is a C-channel shaped column with a cap and a base, all composed of A36 steel. A downward vertical load is applied at the top of the column that will cause it to buckle. DRD introduces the methodology of solving a buckling problem: from a simple Eigenvalue, or linear buckling analysis to a nonlinear buckling analysis where an elastic-plastic material model is employed to simulate permanent deflection and local instability. Students will learn the workflow analysts typically use to solve buckling problems.

Workshop 4b – Snap Through Analysis of a Spherical Tank Section Using Stabilization

A section of a curved tank needs to be analyzed to check deflections and stress. This geometry will buckle when a sufficient load magnitude is applied. Solution restarts and the stabilization feature is utilized in this workshop.

Workshop 5a – 2D Axisymmetric Analysis of a Hyperelastic Rubber Seal with Nonlinear Contact

This four part assembly model has two rubber parts modeled using a hyperelastic material model. Students import experimental data into the Workbench Engineering Data module and curve fit it to create Mooney-Rivlin constants. Initially the model does not converge, and students must modify the model to get it to converge. The model also provides an opportunity for students to experiment with different nonlinear contact formulations including pure penalty, augmented Lagrange, and normal Lagrange.

Workshop 5b – 2D Axisymmetric Analysis of a Hyperelastic O-ring with Fluid Pressure Penetration Loading

This model is comprised of three parts – a cylinder, ring, and seal. The cylinder enters the bore and contacts the seal to produce pressure between the cylinder and ring. Ideally this pressure would be great enough to keep fluids from breaking the seal. The second step applies fluid pressure to the exposed portion of the seal and continues to be applied to the portions of the seal that ‘peel away’ from the cylinder or ring. This fluid pressure penetration capability in Ansys is critical in determining seal performance.

Workshop 5c – 2D Axisymmetric Analysis of a Hyperelastic O-ring with Nonlinear Contact, Using Nonlinear Adaptive Remeshing (NLAD)

This model contains a tube, sleeve, o-ring and swaging body. The swaging body is pushed down, causing the tube to be plastically deformed into the seal, which is a hyperelastic body. A pressure is applied to the inside of the tube at a subsequent time. The o-ring undergoes severe deformation; the Nonlinear Adaptive Remeshing technique is used to remesh the model during the solve process automatically to get a completed solution, rather than the user remeshing manually if the model fails to solve.

Workshop 6a – Nonlinear Contact Analysis of Steel Enclosure with Bolt Pretension

This four part assembly is held together with a pretensioned bolt. Students use Simulation bolt pretension to load the model. The objective of the model is for students to gain a thorough understanding of Simulation bolt pretension. This model also provides additional practice in modeling nonlinear contact.

Workshop 6b – Analysis of a Pump Fluid End with Bolt Pretension

This pump assembly is held together with four pretensioned bolts. Students use load steps to sequentially pretension the bolts one step at a time and then apply additional loads.

Workshop 7 – Stress Analysis of Gearbox Casing Subjected to Static Loads including Plasticity

This gearbox casing is subjected to force and torque loading and the objective is to determine peak stresses in the structure. Students will use the submodeling process, which is based on St. Venant’s Principle, to build a coarse-grid model, take the displacements from locations within the coarse-grid model and apply them to a fine-grid model boundaries. Use of plasticity will be required to get accurate stress beyond the yield strength of the material.

Ansys SpaceClaim will be used to create the fine-grid model using the coarse-grid model as input.

Workshop 8 – Nonlinear Contact Analysis of a Control Valve including Gasket Behavior

This control valve has two gaskets, and the objective of the analysis is to optimize the gasket design. Workbench does not yet have gasket elements, so students use DRD developed commands objects to add gasket elements to the model. The model also involves bolt pretension, pressure, mechanism forces, and thermal loads. The model requires linear and nonlinear contact types. Students define temperature dependent material properties.

The initial design does not have a viable gasket design, and students use a design parameter and DesignModeler to modify the design to achieve an optimum gasket design.