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 durabilityvalidation methodologies are generally employed for high volume, high value, high risk situations where cost is justified.