Introduction to CAE for Strength Analysis: Learn from the Basics to Avoid Failure

 

Here, in mechanical designThe Basics of Strength Analysis."　notes.

 

When I myself started learning strength analysis as a mechanical designer, I was often puzzled by the many technical terms and did not know where to start.　　In particularMany explanation sites that come up when searching for "strength analysis CAE" may assume a certain level of knowledge, making it a little difficult for beginners.　You may feel that

 

In the course of designing machinery, I am currently working to provide information on strength calculations for individual parts, as well as strength calculations for frames, walkways, hoist rails, and so on, to the extent that I can perform analysis in response to requests from our customers. (By "as much as possible," we mean as much as we can do with PC specs and CAD add-in type analysis.)

 

In this article, for those who have the same concerns as I did in the past, I will explain in detail, one by one, everything from the basics of "What is CAE in the first place? and the meanings of technical terms that beginners tend to stumble upon, will be explained one by one in detail.　　From the basic concept of strength analysis, specific methods, practical ideas, various types of analysis, and the concept of appropriate software, we will provide you with the information you need to take the first step in strength analysis.Covers basic knowledgeThe company is doing so.

 

First, you will understand the basic concepts of strength analysis and CAE and their importance, and finallyPractical knowledge to avoid mistakes and regrets in analysis　The program is structured to ensure that students learn step by step in the process of acquiring

Strength Analysis What is CAE? Basic Knowledge for Beginners

In this chapter, we will discuss the basic concepts of strength analysis and CAE.　　Understand why CAE is important now and what the theory underlying the analysis is.

 

Why CAE will change manufacturing

CAE stands for Computer Aided Engineering.　This is a technical system that utilizes the computing power of computers to virtually evaluate and predict the performance of products.　　It plays a central role in modern product development because it allows the performance of a product to be verified on a digital model created on a computer before a physical prototype is built.

 

This technology was originally developed in cutting-edge fields such as aerospace, but is now used in all industries, from automobiles and home appliances to medical equipment.　　In addition, it contributes to improving safety not only in the products we see in our daily lives, but also in the workplaces that support manufacturing.

 

Examples include the platforms of production equipment in operation in factories, inspection walkways for the safe movement of workers, and hoist rails for suspending heavy objects.　These structures, if destroyed, could lead directly to serious industrial accidents.　　For this reason,Strength standards set forth in the Industrial Safety and Health Law and the Safety Regulations for Cranes, etc.　The use of strength analysis to thoroughly verify the safety of products in advance to confirm that they meet the requirements of the "Safety Standards for Products and Services" (SSS) is spreading, and the importance of this technology is increasing beyond product development as a technology to protect the safety of workers.

 

 

Verify product safety with strength analysis

Strength analysis is one of the most fundamental of the many areas of analysis handled by CAE　It is.　　This analysis is performed to ensure that a product or component will not fracture or deform excessively when forces are applied to it.

 

For example, in bridge design, we calculate whether a bridge can withstand the weight of passing vehicles and wind forces.　　For example, in designing a bridge, we calculate whether it can withstand the weight of a passing vehicle or the force of wind.　　Thus,The main purpose of strength analysis is to predict in advance whether the product will have sufficient strength and rigidity to withstand the various forces expected in the environment in which it will be used and to ensure safety.It is.

 

 

Simulation reduces prototyping costs

Simulation is an experiment that simulates a real phenomenon on a computer.　It is.Simulation in strength analysis　applies virtual forces and pressures to a 3D model of a designed part to calculate where the forces are concentrated and how they deform.

 

Traditionally, such verification has been done by building physical prototypes and repeating experiments.　　However, the production of prototypes takes a great deal of time and money.　　For example, the cost of conducting a single crash test of an automobile is enormous.CAE simulation can replace or reduce many of these physical experimentsto the

 

This allows design problems to be identified and corrected early in the development process.　　This approach, called "front-loading," prevents significant rework in later stages of development, resulting in shorter development times and dramatic cost savings.

 

 

What software is needed for strength analysis?

Many people who are about to start strength analysis have the question, "Which software should I choose?　　While there is a wide variety of software on the market, there are two main types: simulation tools that are add-ins to 3DCAD and simulation-specific software.　　Which one to choose depends on the purpose and frequency of the analysis, as well as the complexity of the problem to be handled.

 

3DCAD add-in simulation tool (designer CAE)

This is a tool that allows strength analysis to be performed directly on the 3DCAD operation screen that is normally used.　It is　　It is also called "designer's CAE" because it is intended to allow designers to easily conduct analysis as an extension of the design process.

 

A typical software is "SOLIDWORKS," a 3D CAD system that has been introduced in many companies.SOLIDWORKS Simulation(I have this one, by the way). (This is mine, by the way.)

• Benefits
  • Easy to learn operation: The biggest advantage is the low learning cost, since the system can be operated on the familiar CAD interface.
  • Smooth linkage with design: Because design changes are immediately reflected in the analysis model, the trial-and-error cycle of "design, analyze, look at the results, and revise the design again" can be performed at high speed.
  • Low hurdles to introduction: Designer CAE is focused on understanding rough performance and eliminating fatal design errors in the early stages of design. For this reason, it is often a relatively inexpensive package to start with.
• Disadvantages: -Disadvantages: -Disadvantages: -Disadvantages: -Disadvantages
  • Limited functionality: Compared to dedicated software, the number of phenomena that can be analyzed may be limited. In particular, "nonlinear analysis" involving large material deformation and complex contact conditions may have limited functionality or be available only in higher-end packages.
  • Accuracy and calculation speed: When solving advanced and complex problems, calculations may take longer or be less accurate than the high-performance calculation engine (solver) in dedicated software.

 

Dedicated simulation software (specialist CAE)

This is high-performance software that specializes in performing strength analysis and various other physical simulations. It is also called "specialist CAE" because it is often used by engineers and researchers who specialize in analysis.

The company boasts a high share of the global market in this field.Ansys MechanicalThe first is "I'm a good person.

• Benefits
  • Advanced and extensive analysis capabilities: A very wide range of physical phenomena can be simulated with high accuracy, including linear analysis, large-scale nonlinear analysis, dynamic analysis, fatigue, thermal, fluid, and electromagnetic fields.
  • Reliable solver: The calculation engine, developed through years of research and development, excels in its ability to stably derive solutions to even complex, hard-to-converge problems.
  • Customizability: Extensibility for more advanced use by experienced users, including scripting capabilities to automate the analysis process.
• Disadvantages: -Disadvantages: -Disadvantages: -Disadvantages: -Disadvantages
  • Difficult to learn to operate: While highly functional, operation is complex and requires specialized knowledge and training to master.
  • Expensive: In general, licensing costs are higher than for CAD add-in type tools.
  • Linkage with CAD: Although linkage functions have improved in recent years, separate data import/export operations may be required between CAD and analysis software when reflecting design changes.

 

Which should we choose?

Neither software is superior to the other; the best choice depends on your objectives.

• Cases where Designer CAE is suited:.
  • Designers themselves want to easily check for basic problems such as lack of strength in the early stages of design.
  • The products handled can be evaluated primarily in the range of linear static analysis.
  • First of all, we want to introduce CAE at a low cost and see its effect.
• Cases where expert CAE is suited:.
  • Highly nonlinear analysis is essential for large deformation of rubber and plastic parts and complex contact between parts.
  • Very high accuracy and reliability are required for the analysis results.
  • There is a department or person within the company that specializes in analysis.

It is a realistic approach for many companies to start with designer CAE, and then consider introducing expert CAE when more advanced problems arise that cannot be solved there.I am sure you will.

 

 

The finite element method, the basic principle of analysis

The calculation method used by most strength analysis software is the Finite Element Method (FEM).　This method approximates an analytical target with complex geometry as a collection of small elements with simple shapes such as triangles and rectangles.

 

Computers cannot calculate the entire behavior of a complex geometry at once.　　Therefore, the behavior of each of these simple elements is calculated based on the basic equations of material mechanics. Then, by combining the calculation results of all these elements and solving the simultaneous equations, the deformation and stress distribution of the entire structure is obtained.

 

This concept of "divide and rule" is the essence of the finite element method, which makes it possible to predict the strength of parts with a high degree of accuracy, no matter how complex their geometry.

 

 

Relationship to hand calculations for learning theory

CAE software is very powerful, but it is only a computational tool.　　To obtain correct results, it is essential that the designer himself have a basic knowledge of material mechanics.　　Particularly for simple geometries, approximate stresses and deformations can be obtained by manual calculations.

 

There are two major advantages to performing manual calculations.　　One is the role of "verification" to confirm that the results of the CAE analysis are within a reasonable range.　　If the results of the hand calculations and the CAE results are far apart, it suggests that there may be some errors in the CAE model setup.

 

The other is to deepen your understanding of physical phenomena.　　Through hand calculations, one can get a sense of which parameters have a significant impact on the results.　　This understanding is a very important foundation for setting appropriate boundary conditions and correctly interpreting results in CAE.

 

 

Strength Analysis CAE Basic Methods and Three Processes

The actual work involved in strength analysis can be divided into three major processes.　　Understanding this sequence of steps is the first step to proceeding systematically with the analysis and obtaining reliable results.　　In this section, we explain what role each process plays.

 

Importance of pre-processing to prepare for analysis

Pre-processing is the preparatory step before running an analysis, and is the process of converting a real-world physical problem into a form that can be understood by a computer.　This phase is arguably the most critical phase that determines the success or failure of the entire analysis.

 

The main tasks are as follows

1. Geometry Preparation: Simplify the geometry by removing minute holes, rounded corners (fillets), etc. that are unnecessary for analysis from the 3D model created in CAD.
2. Mesh Creation: Divide the geometry into small elements (mesh), which are the computational units of the finite element method.
3. Material Definition: Sets the physical properties of the materials the model is made of.
4. Boundary condition setting: Define how the model is fixed (constraint conditions) and what forces are applied (load conditions).

 

As the phrase "Garbage In, Garbage Out" suggests, if the pre-process settings are incorrect, the results obtained will be meaningless no matter how sophisticated the computer is.

 

 

Role of the solver in performing complex calculations

A solver is a program that actually performs calculations based on information defined in a preprocessor.　　At its core, it solves a huge number of simultaneous linear equations based on the finite element method.

 

This calculation process is essentially automated by the software and requires little direct user interaction.　　The user simply instructs the software to perform the calculation and waits for it to finish.　　However, if the calculation does not converge or stops with an error, the user should go back to the pre-process settings and review the mesh and boundary conditions.

 

 

Post-processing to visualize results

The post-processing stage is the stage of visualizing the vast amount of numerical data calculated by the solver into a form that is intuitively understandable to humans.　The calculation results, as they are, are merely a series of numbers.

 

The post processor displays these numbers in the following format

• Contour diagram: A diagram showing the magnitude of stress and displacement, etc., expressed in different colors. Hazardous areas can be identified at a glance.
• Deformation diagram: A diagram showing how the model deforms under load, superimposed on the original geometry. Deformation can also be exaggerated.
• Graph: Graphs show changes in stress and displacement at specific locations.
• Animation: Animation of model motion for time-varying analysis (e.g., kinematic analysis).

 

The designer looks at these visualized results and makes engineering decisions such as whether there are any design problems, whether the strength is sufficient, and, if necessary, considers design changes.

 

 

Mesh quality determines analysis accuracy

As mentioned above,Meshing is an important part of the pre-processing process, and its quality has a direct impact on the accuracy of the analysis results.　　However, this meshing is a process in which many designers frequently encounter errors, so to speak.A process that can be called the first barrier　It is.

 

 

Why do mesh errors occur?

The main cause of mesh errors is the complexity of the geometry of the CAD model.　In particular, errors are more likely to occur in the following cases

 

• Minute features (features): Very small fillets (rounded corners), chamfers, engraved logos, etc. that are necessary for design but do not affect the overall behavior of the analysis can cause errors when trying to generate extremely small meshes.
• Complex surfaces: Even surfaces that appear smooth may be a collection of many tiny surfaces in the data, which may not be handled well by the mesh generation algorithm.
• Assembly Models: The problem is compounded by assembly models that contain multiple parts, especially standard parts such as bolts and nuts. Tiny gaps and interferences between parts, as well as details such as bolt threads, make mesh generation significantly more difficult.

 

Mesh creation in practice: model simplification (de-featuring)

Therefore, an essential step in efficiently creating a high-quality mesh is a process called "simplification" or "de-featuring" of the analysis model.　　This refers to the process of intentionally removing unnecessary geometry from a CAD model to the extent that it does not affect the purpose of the analysis.

 

• Removal of fillets and holes: Small fillets and holes in areas that are not subject to stress evaluation are boldly removed. This has the effect of reducing the number of mesh elements and calculation time.
• Integration and simplification of parts: Taking bolted joints as an example, instead of modeling the complex shapes of bolts and nuts as they are, models can be greatly simplified by simulating them with beam elements or simple cylinders, or by expressing the presence of bolts in terms of constraints.

 

This simplification is an area where experience is important, as it requires engineering judgment as to how much to simplify.

 

 

Practical meshing techniques

In parallel with model simplification, there are several techniques for mesh cutting.

 

• Local Mesh Partitioning: Only the mesh in areas where you want to see detailed results, such as around corners and holes where stresses are expected to be concentrated, is locally refined. This reduces overall computational cost and improves the accuracy of analysis in critical areas.
• Element Type Selection: The elements that make up a mesh include tetrahedral (tetra) and hexahedral (hexa) elements. While tetrahedral elements can easily handle complex shapes automatically, hexahedral elements are generally considered more accurate for the same number of elements. It is effective to use hexahedral elements for meshing as much as possible and tetrahedral elements only for difficult parts.
• Checking quality indicators: Many CAE software have the ability to check indicators of mesh quality (aspect ratio, Jacobian ratio, etc.).　Even if no errors are found, the process of checking for the presence of many elements of poor quality (elongated or crushed elements) and manually correcting them if necessary will increase the reliability of the results.

 

 

Correct setting of boundary conditions that mimic reality

Setting boundary conditions is an extremely important task, as it defines the conditions under which the analytical model is placed in the real world.　　If the settings here are not physically appropriate, the analysis results will be far from reality.

 

binding condition

Define how to anchor the model so that it does not move.　　If this is not sufficient, the model will fly away when a force is applied, and the calculation will stop with a "rigid body motion" error.　　For example, the software functions to simulate realistic support conditions such as "completely fixed with bolts" or "supported only by pins with free rotation.

 

Load condition

Define what forces will act on the model.　　The model must accurately model the actual loads that the product is subjected to, such as "uniform pressure on a surface," "force concentration at a specific point," or "the dead weight of the entire part.

Setting boundary conditions is not a mere software operation. It is the part that most tests the designer's engineering acumen, how to appropriately simplify the complex physical phenomena of reality and incorporate them into the model.

 

 

Strength Analysis Selected by Purpose Typical Types of CAE Analysis

Strength analysis, in a nutshell, encompasses many different types of analysis methods.　　The key to accurate and efficient design verification is to select the appropriate type of analysis according to what phenomena you wish to evaluate and for what purpose.　　This section describes the typical types of analysis frequently used in mechanical design.

 

Overview of basic linear static analysis

Linear static analysis is the most basic and most widely used analysis method.　　As the name suggests, it deals with "linear" and "static" problems.

 

Assumptions for linear static analysis

There are three major assumptions that must be made for this analysis to be valid

1. The material must be linear: the force and deformation are proportional (Hooke's law), and only the "elastic range" is treated, i.e., the material completely returns to its original shape when the force is removed.
2. Minimal deformation: Assume that the deformation of the part is very small and that the deformation does not change the stiffness.
3. Loads are assumed to be static: loads are applied slowly and do not vary in time.　Dynamic forces such as impact or vibration are not considered.

Since many mechanical components are designed to function safely within the limits of this linear static analysis, it is a very useful first step in strength analysis.　　It also has the advantage of being relatively inexpensive and easy to obtain stable results.

 

 

Nonlinear analysis dealing with large deformations and contact

In the real world, there are many phenomena for which the assumptions of linear static analysis do not hold.　　Nonlinear analysis is used in such cases.
There are three main cases where nonlinear analysis is required

 

1. Material non-linearity: This is the case when a material is deformed beyond its yield point and is irreversibly deformed (plastic deformation), or when dealing with materials such as rubber, where the force and deformation are not proportional to each other.　Examples include metal press work and deformation of plastic parts.
2. Geometric non-linearity: when the amount of deformation is large and the stiffness changes accordingly, such as when a thin plate deflects greatly or a long, thin bar bends under compression (buckling).
3. Boundary condition nonlinear: This is the case when dealing with the behavior of parts coming into contact with each other, separating, or sliding with friction.　　This is essential in the analysis of assemblies consisting of multiple parts, such as gear meshing or connector insertion/removal.

 

Nonlinear analysis can simulate more realistic behavior, but requires specialized knowledge because it is computationally time consuming and complicated to set up.

 

 

Eigenvalue analysis to avoid resonance

Eigenvalue analysis differs slightly from conventional analysis in that it does not apply external forces.　　Instead, it is an analysis that investigates the "individuality of swayability" that a structure possesses.　　Specifically, it calculates at what frequency the object tends to vibrate (eigenfrequency) and in what form it shakes (eigenmodes).

 

The main purpose is to avoid the dangerous phenomenon of "resonance.　　If the frequency of an external vibration, such as a motor or engine, happens to coincide with the natural frequency of a component, the shaking will be rapidly amplified, leading to loud noise and, in the worst case, destruction.

 

Eigenvalue analysis is extremely important in the design of products such as automobile engine components, bridges, and aircraft wings, where vibration directly affects performance and safety.

 

 

 

Thermal stress analysis due to temperature change

Thermal effects cannot be ignored when products are exposed to large temperature changes in the environment in which they are used.　　Examples include automobile engines and brakes, and internal components of electronic equipment.

 

Thermal analysis is typically performed in two steps.

1. Heat transfer analysis: First, we calculate how the temperature will be distributed throughout the product based on the heat-generating components and ambient temperature conditions.
2. Thermal Stress Analysis: Next, the temperature distribution obtained from the thermal conduction analysis is given as a load.　　The material expands as the temperature rises and contracts as the temperature falls.　　If this deformation is prevented (restrained) by surrounding components, an internal force (thermal stress) is generated. This thermal stress is calculated to evaluate whether the part will be destroyed.

 

Thus, the purpose of thermal stress analysis is to evaluate the deformation and stress caused by temperature changes.

 

 

Fatigue analysis for cyclic loading

Even a part that seems perfectly safe when subjected to a single large force may gradually develop invisible, minute cracks due to repeated application of relatively small forces, eventually leading to sudden failure.　　This is "fatigue fracture.

 

Fatigue analysis is used to predict the life of parts subjected to such repetitive loading.　　Examples include shafts that rotate continuously and automotive suspension components that constantly vibrate while the vehicle is in motion.

 

In this analysis, fatigue property data for each material, called "S-N diagram," is used.　　This graph shows the number of repetitions of a certain magnitude of stress (Stress) that will lead to failure.　　By comparing the S-N diagram with the stress of the part determined by static analysis, etc., it is possible to predict how long the part can be safely used.

Analysis Type	Key questions to resolve	Main input	Typical applications	Precautions and Prerequisites
linear static analysis	How strong and stiff is it against static loads?	Load and restraint conditions	Strength and stiffness evaluation of general structural components	Only if the three assumptions of microdeformation, linear material, and static loading hold.
Nonlinear Analysis	What about behavior involving large deformation, contact, and material yielding?	Nonlinear material data, contact definition	Plastic snap-fit, sealing parts, metal press molding	High computational cost and may be difficult to converge. Requires specialized knowledge.
eigenvalue analysis	At what frequencies and how easily does it vibrate?	(no load required), density	Avoiding resonance caused by vibration from motors and engines, wind-resistant design of bridges	The calculated deformation is a relative shape, and the amount of displacement itself is meaningless.
Thermal Stress Analysis	Will temperature changes destroy it?	Temperature distribution, thermophysical properties (coefficient of thermal expansion, etc.)	Engine exhaust system components, electronic circuit boards, brake discs	Usually, this is a two-step analysis in which the temperature distribution obtained from the heat transfer analysis is applied as a load.
Fatigue Analysis	How long can it hold up to repeated loads?	S-N diagram, stress history	Vibrating structures such as rotating shafts, suspensions, aircraft wings, etc.	Stress results obtained from static analysis, etc., and fatigue property data (S-N diagram) of the material are required.

 

 

Strength Analysis Indicators to correctly evaluate CAE results

After performing the analysis, the ultimate goal is to correctly interpret the results obtained in the post-process and provide feedback to the design.　　Although post processors visualize a variety of indicators,Five basic indicators that are particularly important in strength assessment, and their meanings and perspectives.Explanation.

 

 

What is the stress that indicates the material's hardiness?

Stress is the resistance force (internal force) generated inside an object when a force is applied to it from the outside, expressed per unit area.　　The unit is usually MPa (megapascal).

 

Simply put, it is a measure of how "hard" a material is resisting external forces.　　The higher the stress value, the greater the load the material is subjected to, meaning it is more likely to be the starting point for failure.　　In post-processing, the stress distribution is color-coded on a contour map to provide a visual indication of where stress is concentrated.

 

 

Displacement indicating the amount of deformation due to load

Displacement is the amount by which a structure has moved or deformed from its original position due to applied loads.　　Units are usually expressed in mm (millimeters).
Displacement is consequently one of the most intuitive and easily understood indicators. In design, it is evaluated from two main perspectives

 

1. Evaluate rigidity: Check to see if the product will not deflect or deform excessively. For example, is the weight of the shelves deflecting too much?
2. Check for interference: Check to see if the deformed parts will not collide (interfere) with other surrounding parts.

 

Animation of the shape after deformation helps the user to intuitively understand the overall behavior of the product.

 

 

Concept of safety factor indicating design margins

The factor of safety is a numerical value that indicates the "margin" that a design should have.　　This is an indicator of the ratio of the maximum stress actually occurring to the limit strength (allowable stress) that the material can withstand.

 

The formula is generally expressed as "factor of safety = allowable stress of material ÷ maximum stress to be generated.

 

For example, a factor of safety of 2.0 means that the component has a margin of safety that it will not fail until a force twice the design anticipated load is applied.　　If the factor of safety is less than 1.0, it indicates that the stress generated exceeds the allowable stress and that failure is highly likely under the loading conditions.

 

The required safety factor value is based on the importance of the product, the impact on human life in case of destruction, and the environment in which it will be used,Design standards and various standards　This is defined by the

 

 

Mises stress to evaluate yield

Mises stress (von Mises stress) is a complex stress state (a combination of tension, compression, and shear) applied to a single point on an object, converted to a single equivalent stress value (a scalar quantity).

 

Role of Mises Stress

This indicator is primarily used to determine whether a ductile material such as steel (a material that elongates and deforms significantly before fracturing) will reach "yield," the point at which it begins to deform permanently.　　Specifically, the maximum value of Mises stress obtained from the analysis is compared to a physical property called "yield stress (yield strength)" of the material.　　If the Mises stress does not exceed the yield stress, the part is within the range of elastic deformation and will return to its original shape when the load is removed.

 

important point

The Mises stress is a scalar quantity that indicates only the magnitude of the stress and has no information about whether the force is tensile or compressive.　　Therefore, when it is necessary to distinguish between different types of stress, it is useful to use it in conjunction with the principal stresses described below.

 

 

Principal stress to evaluate fracture

Principal stress is the vertical stress in a special direction in which the shear stress is zero at a point inside an object.　　There are three mutually orthogonal directions, called maximum principal stress, intermediate principal stress, and minimum principal stress, in order of increasing value.

 

Role of principal stresses

Principal stresses, unlike Mises stresses, have a direction of force (vector quantity) and a sign.　　Positive values imply tensile stress, while negative values imply compressive stress.　　This property is often used to evaluate the strength of brittle materials (materials that fail with little or no deformation) such as cast iron and ceramics. Since these materials are generally susceptible to tensile stress, the maximum principal stress value is checked to ensure that it does not exceed the tensile strength of the material.

 

Use with Mises Stress

In practice, it is effective to use a Mises stress contour diagram to roughly identify the high-stress hazardous areas first, and then check the principal stresses in those areas for detailed diagnosis of whether tension or compression is the cause.

 

 

Practical knowledge for failure-free strength analysis CAE

CAE is a powerful weapon for designers, but if it is used incorrectly, it can lead to erroneous conclusions and, in turn, increase design rework. In this chapter, we will explain five practical knowledge and attitudes to avoid the traps that beginners tend to fall into and to obtain reliable analysis results.

 

 

Data on material properties essential for analysis

In CAE analysis, as important as the geometry data of a model is the material property data that describes what the model is made of. Based on the input material properties, the software calculates the behavior of the model when forces are applied. Therefore, using inaccurate material data will naturally lead to inaccurate results.

 

Most CAE software comes with a database of common industrial materials, but when special materials are used or higher accuracy is required, it is important to refer to the data sheets provided by the material manufacturer or conduct material tests to obtain physical properties as needed.

 

 

Young's modulus, which indicates the hardness of a material

Young's modulus is the most basic physical property that indicates the hardness or resistance to deformation of a material.　It is also called the modulus of longitudinal elasticity.

Physically, Young's modulus is a constant of proportionality in the elastic range of the relationship between stress (internal resistance) and strain (elongation) when a material is pulled.　　The higher the value of Young's modulus, the more rigid the material is (e.g., steel), and the lower the value, the more flexible the material is (e.g., rubber), which is more easily deformed.

This value is a critical parameter in stiffness evaluations and eigenvalue analyses to calculate component deflection.

 

 

Poisson's ratio indicating the ratio of deformations

Poisson's ratio is another important elastic property of a material.　　Imagine the phenomenon that when a rubber band is pulled, it becomes thinner at the same time as its length is extended.　　In this way, when a material is pulled (or compressed) in a certain direction, how much does it shrink (or expand) in the direction perpendicular to that direction?The ratio is shown as Poisson's ratio　The first is

For most materials, this value falls between 0 and 0.5, with many metallic materials having a value around 0.3.　　Along with Young's modulus, Poisson's ratio is another property that is essential for accurately simulating the deformation behavior of materials.

 

 

Stress singularities that produce false results

A stress singularity is a phenomenon in which the stress is theoretically infinite at a specific point in the analytical model.　　This is not an actual physical phenomenon, but a computational problem in the finite element method due to the modeling of the geometry.

 

Causes of occurrence and how to recognize them

Stress singularities occur primarily at sharp corners of the geometry (pin angles) and at points or lines where loads or restraints are set.　　At these locations, the area used to calculate the stress (force divided by area) is theoretically close to zero, so the stress value is infinitely large.

 

The distinguishing feature of a stress singularity is that the finer the mesh is made in the area, the more the stress value does not converge to a specific value and continues to increase.

 

 

approach

The novice is apt to see this abnormally high stress value, which appears bright red on the contour plot, and mistakenly believe that there is a problem with the design.　　However, since this is a computational artifact (an apparent result), the stress value at that point itself should not be evaluated.　　The solution is to evaluate the stress values at some distance from the singularity or, if possible by design, to add a small rounding (fillet) to the sharp corner that is causing the singularity, thereby avoiding its occurrence.

 

 

Reliable strength analysis Improved accuracy for CAE

In order to obtain reliable analysis results, there are a few important prerequisites to keep in mind, in addition to software operation techniques.

 

Verification and Validation

It is always important to be skeptical of the analysis results.　If possible, make it a habit to check whether the results are within a reasonable range by comparing them with the results of manual calculations and past experimental data of similar products (validity check).　　Also, recalculating with a different mesh fineness to see if the results do not vary significantly (mesh convergence check) is an effective way to ensure the reliability of the results.

 

Start with a simple model

As a beginner, start with a simple model and simple analysis (linear static analysis) rather than suddenly trying a complex model and analysis.　　Building on the knowledge gained there is a shortcut to success in more advanced analysis.

 

 

Reexamine boundary conditions

When analytical results differ significantly from intuition or experience, the cause is often an error in the setting of boundary conditions.　It is important to examine the setup once again against the reality of the situation to ensure that the model is really fixed that way and that the loads are applied correctly.

Symptoms / Error Messages	Possible Causes	Recommended remedies
Calculation stops with "Rigid Body Motion" error.	Insufficient constraints, leaving the model free to move (translate or rotate).	Review the constraints so that the model is fixed in all six degrees of freedom, XYZ translation and rotation. First, try fixing the model completely and see if the calculations flow.
Maximum stresses are unrealistically high and continue to rise further with finer meshes.	Stress singularities due to sharp angles and point loads are occurring.	Ignore the stress values at the singularity itself and evaluate it at a small distance. If possible, go back to the CAD model and add a small fillet to the corner that is causing the problem.
Calculations do not converge in nonlinear analysis.	Multiple factors are possible, including unstable contact settings, too large a time step, and inappropriate material models.	Reduce the time step. Review the contact definition. Revert to a simpler problem set-up and gradually increase complexity.
The deformation is plausible, yet the stress is almost zero.	Incorrect magnitude of load or inconsistent system of units (e.g., confusion between N and kN).	Recheck that all units (shape, material, load) are consistent. Calculate load values by hand or other means.

 

 

Reliable strength analysis Improved accuracy for CAE

Below are bullet points summarized in this article.

 

• CAE is a technology that simulates physical phenomena on a computer.
• Strength analysis is essential to ensure product safety and reliability
• Simulation　Finding problems early in the development process and reducing costs through
• The basic principle of analysis is the finite element method, which divides a complex geometry into simple elements
• Hand calculations are important to validate CAE results and deepen understanding of physical phenomena
• The analysis process consists of three stages: preparation (pre-process), calculation (solver), and result evaluation (post-process).
• Pre-process mesh, material properties, and boundary condition settings determine the reliability of results
• Linear static analysis, nonlinear analysis, eigenvalue analysis, thermal stress analysis, fatigue analysis, etc. depending on the purpose
• Linear static analysis is the basic analysis when deformation is small and the material is in the elastic range
• Nonlinear analysis deals with more realistic phenomena such as large deformations, plastic deformation of materials, and contact between parts
• Evaluating the results involves a comprehensive evaluation of indicators such as stress, displacement, and factor of safety.
• Mises stress is used to evaluate the yield of ductile materials, and principal stress is used to evaluate the fracture of brittle materials and to investigate the direction of stress
• Young's modulus andPoisson's ratio　is a fundamental physical property that determines the deformation behavior of a material
• Stress singularities are a matter of calculation and should not be evaluated by the stress value at that point
• Always question the results, and an attitude of comparison and verification with manual calculations and experimental data will lead to improved accuracy.

 

That's it.