Ensuring that performance, durability and business targets are met for any new or redesigned product begins well in advance of any preliminary drawings, material, tooling or other manufacturing decisions.  From the outset, it is critical to understand how the product will be used (and abused) in the real world while identifying the business goals and parameters driving the project.

This information helps ensure that the design will meet durability, performance and ROI targets and determine the optimum product design validation approach. For designers and manufacturers of specialty vehicles or off-highway equipment, durability validation is both critical and challenging.

Design Validation

Validating the design allows manufacturing to proceed confident that products/sub-systems/components will perform as expected and meet lifecycle requirements. In the past the process consisted almost solely of constructing and testing a series of physical prototypes. Validation began with running a prototype through a series of tests until failure occurred. The process was repeated ad nauseam with newly designed prototypes until either a design was validated or the project, running low on time and money, was deemed good enough.  Too often the result was a product that under-achieved in meeting performance and monetary targets.

Today computer-aided design (CAD) and simulation tools, such as finite element analysis, automate and accelerate the process. Validating designs in the early upstream stages of product development, well in advance of manufacturing, goes a long way to reducing warranty and legal claims, gaining market share, boosting innovation, and increasing customer satisfaction.

Products in the Real World

Expectations and reality can sometimes differ radically.  To help ensure that products will in fact operate successfully in their intended environment, design validation is driven whenever possible by tangible and quantifiable data. Such baseline operating data is collected in numerous ways.

Unattended Testing is one reliable method for collecting real-world operating data. In the process vehicles and equipment are instrumented with data collection and recording equipment and put through operation. Gathering large sets of data over an extended period of time ensures that usage is accurately reflected and the occasional anomaly is captured. Armed with this information, designers/manufacturers can explore a range of design alternatives and validate the design for manufacturability, durability and reliability.

It’s important to understand that, when in the customer’s hands, a product/sub-system/component may push or exceed the limits for which it was intended.  Likewise, harsh conditions and excessive forces to which the equipment may be subjected often far exceed that for which it was designed.

Understanding sometimes vague or unanticipated customer usage scenarios and operating environments directly influence durability targets. Whether exceeding maximum load limits, traversing excessively rugged terrain, brutal climate conditions or neglecting maintenance schedules, product design must account for scenarios that often go far beyond the expected.

Product Development Business Drivers

From a relatively simple redesign to a new product launch, organizations must weigh many factors.

Knowing where you want to go and how you want to get there is critical to launch any product development campaign. And while these and other considerations are important the overriding driver for and new or redesigned product is the impact that it will have on the company’s bottom line. Validation is a proven key to mitigating risks.

Fundamental Approaches to Validation

Today there are two fundamental approaches for validating products related to equipment or specialty vehicles.  Each is proven, effective and technically sound; and each has its advantages:

This is by no means to suggest that physical testing and simulation are mutually exclusive. Many larger organizations often employ both. Regardless of the approach, any legitimate product validation approach should contain elements of each.

Test-Centered Validation Approach

A test-centered approach to durability validation is rooted in capturing and analyzing physical performance data as the vehicle/equipment is put through operation. Data is collected by instrumenting the vehicle with strain gages and accelerometers to measure deflection or quantify how the system, subsystem, component reacts under certain loads and conditions. Data can be collected in numerous ways ranging from a controlled laboratory environment, a representative environment, or in the field under typical operating conditions. These tests can vary depending on whether we’re dealing with a system, sub-system or component.

System Level Durability Validation

On a systems-level (and with certain sub-systems) hydraulic test rigs are used to recreate usage conditions within a laboratory or controlled environment.  System-level test-centered validation generally comes in two forms: Durability Rig Testing, Extended Operating Testing.

Durability Rig Testing

System-level durability testing is often done via a hydraulic test rig within the controlled confines of a laboratory.  This entails continuously subjecting the system to forces generated by the test rig over an extended period of time to recreate field usage conditions.  Doing so allows long-term effects to be measured in a relatively short period of time.

Simulation plays a role in the process as Finite Element Analysis is used to determine where strain gage and accelerometers should be initially placed on the system. Loads and responses from baseline testing is used to define operating environments and associated durability parameters. The process then moves to the development of drive files to control the test rig in order to recreate forces to which the system will be subjected.  After it has been put through its paces on the test rig, the system is inspected for cracks and other structural damage.

Extended Operating Testing

Another popular durability validation method is the continuous operation and testing of a vehicle or piece of equipment on representative environments.  This might include a test track, proving grounds, in-field usage and so on.  Similar to hydraulic rig testing, vehicles are typically instrumented with data collection equipment to measure strains and accelerations and determine extent of accelerated damage. Analyzing large amounts of accumulated data provides engineers with insight into product performance and a means to objectively validate the design.

Subsystem and Component Level Durability Validation

When separated from the system, each sub-system or component may perform as designed. Sometimes, however, when incorporated into a system interaction with neighboring components or sub-systems can introduce unexpected forces or vibrations for which the component/sub-system was not designed causing failure.

To measure the performance of sub-systems/components within the context of the collective system, forces and/or accelerations are obtained from system-level tests. These forces are then replicated using a hydraulic or electrodynamic shaker during the testing of components or sub-systems.

Advantages

A significant advantage to test-centered validation is the ability to physically see, touch and measure the product being validated.  At the same time in-field testing allows products to be validated against, not only anticipated usage scenarios, but for anomalies and other rare events outside the anticipated scope of operation to be captured and measured.  This allows vehicles/equipment to be designed to meet a wide range of possibilities.

On the downside, complex loading is not easily applied to test rig testing.  Additionally, physically testing sometimes multiple prototypes can be time consuming, labor-intensive and costly. For automotive applications, for example, costs related to rigs, track time, labor, equipment, along with modeling and analysis must be factored. Consequently, test-centered durability validation methodologies are generally employed for high volume, high value, high risk situations where cost is justified.

Simulation-Centered Validation Approach

While a simulation-focused approach to validation is heavily reliant on Finite Element Analysis, there remains a need for physical prototype testing; albeit in a very limited capacity.  Nonetheless, this heavily digital approach is fast, reliable and relatively inexpensive when compared to Test-Centered Validation.

Data obtained from testing units (often competitive brands) similar to a new design provides approximate loading environments. For specialty vehicles and off-highway equipment this might include collecting data from the field via unattended testing.  Collecting data over long periods of time provides an understanding of both common and rare (but significant) loads that the vehicle/equipment may encounter over its service time.

The more one understands how the product will be used by the customer, including the loads and response mechanisms, the more effective simulation will be. And the better the simulation, the less rework, less time lost, and lower expense.

Data Collection & Analysis

Effectively validating a finite element model requires that representative, proportionate, and extreme (within reason) forces are applied the model.  This ensures that the model is being evaluated against accurate operating parameters to which the final product will be subjected.

These forces are collected manually through testing physical prototypes, current model or competitive vehicles. This generally includes affixing accelerometers and strain gages to key locations throughout the vehicle and putting the equipment through operation.  It is recommended that data be collected both while in normal service and proving grounds testing.  In this way forces, acceleration, twist, pitch and strain are quantifiably measured and captured for each key location on the vehicle.

In the next phase, field test data is compared to that collected in the field or proving grounds.  The intent is to qualify an accelerated durability test cycle. Data collected from load cells placed on the vehicle is compared to strain responses to identify significant load cases representing vehicle usage. These load cases (e.g. body twist, pitch, strain, etc.) are ranked based on damage calculations. Similarly proving ground data is associated with field test load cases and scaled based on damage calculations. A set of accelerated durability proving ground events is defined and ranked from these comparisons.

Engineering analysis (simulation) software is used to run an accelerated durability simulation. This helps accurately predict proving ground test performance. Static and inertial load cases are developed from field and proving ground data. This includes the association of load cases with the measured strain responses and is helpful for reading FEA model correlation activities.

Although static FEA analysis is likely sufficient, test results sometimes indicate a need to address system dynamics. When this is the case a dynamic model, predicting significant low frequency vibration modes, is created and correlated to modal testing.

Advantages

Simulation-Centered Validation accelerates product development and increases innovation measurably.  Making and evaluating design changes through modeling and simulation allows multiple design iterations to be explored quickly and cost-effectively without the time and expense of building and testing numerous physical prototypes.

Organizations driven by time to market or innovation or those with a limited budget will benefit from Simulation-Centered Validation.

What’s the Best Approach?

Test-Centered and Simulation-Centered Validation can be equally effective. And while both contain elements of testing and simulation the emphasis and roadmap to validation is very different. Consequently organizations should take the time to scrutinize validation resources at their disposal, identify the business drivers and weigh the pros and cons of each approach.

With decades of testing and engineering analysis experience, Six D Testing & Analysis (6D) has pioneered many of the testing and simulation tools, technologies, and best practices now standard throughout product development, validation and troubleshooting.  Today 6D works with its customers to support both test-centric and simulation-centric product validation.