Vibration testing and validation
By condensing a lifetime of stress and wear into a short period of time, vibration tests can reveal hidden design weaknesses.
We need to be sure that products can cope with the shocks and stresses of their service life. For example:
- A mobile phone must be able to withstand bouncing around in a backpack as well as being dropped on the floor several times. If it cannot cope with this general day-to-day use, warranty costs will explode for the manufacturer resulting in a real risk of brand deterioration and of customers looking elsewhere the next time they buy a new phone.
- A satellite has to be able to survive the excessive vibrations from being launched into space. If it is faulty, the investment in the development and building of the satellite may be jeopardized.
In order to ensure that the products customers receive are intact and fully-functional, it is essential that they can survive the journey from when they are boxed at the factory until they arrive at the end destination.
Moreover, beyond merely withstanding short-term physical forces, developers need to ensure that their products will maintain the integrity and quality that represents the brand in the longer term. Product qualification and verification is done through extensive simulation in the development phases, but simulation is not enough. It is also necessary to do physical testing on prototypes and end-of-line items, both to validate simulated results and to prove product durability to customers.
Ensuring product integrity
Vibration testing helps manufacturers to ensure quality, reliability and durability of complete products and their components. Vibration tests can reveal design weaknesses that would only become apparent during transport, deployment and use – like a helmet hitting the ground. Some of these tests, such as buzz, squeak and rattle (BSR) on vehicle interiors, can also detect the development of unwanted noise. For environmental testing such as highly accelerated lifetime testing (HALT) and highly accelerated stress screening (HASS), it is necessary to combine vibration testing with environmental chambers to add the expansion stresses of rapid heating and cooling. These tests are typically conducted on industrial and electronic components and products, on medical equipment and on military hardware.
Vibration test profiles
Where do the actual vibration test profiles originate? Customers, end users or manufacturers who incorporate a component into an assembly, often define vibration test specifications and procedures themselves. These are typically based on experience and knowledge of which design solutions work well and which don’t. Vibration test can provide a more structured approach to understanding failure modes and defects that are caused by vibration.
Testing according to standards
Many vibration testing profiles are defined by standards developed over many years. There are a lot of them and they are often dedicated to specific applications and products. Examples include DIN, ISO, BS, MIL, IEC and ASTM. The use of testing according to standards is especially the case for the aerospace and defence industries. These include MIL-STD-810, NATO STANAGs and AS/EN9100.
Selecting a system
It is essential that your system is appropriate for the test – able to input the necessary vibration types and able to handle the forces generated when testing specific payloads. Above all, self-monitoring of resulting vibration levels is vital to ensure that your test object is not stressed more than necessary.
There are many ways of configuring systems to meet your testing requirements. Here are some common types of vibration test and our suggestions for systems to conduct them. There are many other ways of configuring systems for specific test types; if your requirements are not met by these specific suggestions, please explore the vibration test product section or contact us to discuss your testing needs.
Durability and fatigue testing help manufacturers to evaluate how well their products and components hold up to typical use. Subjecting components, assemblies and finished products to vibration that mimics real conditions is essential for assessing if products are fit for purpose throughout their service life. When conducting durability testing, products are either tested to meet certain standards, often defined by OEMs and top-tier suppliers, or they are shaken to destruction.
Durability testing is often repetitive, so it needs to be easy to set up, conduct and sign off. The ability to store test profiles via the controller software, and to reuse them repeatedly, supports simple test execution.
For durability testing, a common system configuration is based on a medium-force air-cooled shaker that can be used in either a vertical or a horizontal configuration, for example, a V875-440 combo. This is a versatile shaker for payloads up to 600 kg (1323 lb), including automotive and aerospace assemblies and subassemblies. The shaker in this system can be replaced to accommodate different size payloads.
To test how products, components and subsystems survive a drop, an induced shock or even a pyro shock, it is common to perform transient shock testing, drop testing and/or impact testing. When conducting shock tests, payloads such as televisions, auto parts or white goods are moved rapidly for a short time period 100 g or 11 m/s, to simulate a car hitting a pothole or a television being dropped under transport.
Automotive OEMs, military and commercial manufacturers have standards for shock testing. These include SAE J1455 for shock and drop testing of vehicles and components, IEC 60068-2-27, IEC 60068-2-29 and IEC 60068-2-31 for classical shock, bump and fall of commercial products, and MIL-STD-810 for classical shock tests and shock response spectrum (SRS) analysis of military systems. The ability to store and reuse standardized test profiles via the controller software supports simple test execution.
For shock testing, we suggest a system based on the V8 medium-force air-cooled shaker with industry-leading displacement of 63.5 mm (2.5 in) and a peak velocity of 1.8 m/s (70.9 in/s). The intuitive LASERUSB controller, whose shock test software offers fast and accurate recording and analysis of shock tests, controls this. For more advanced shock analysis, PULSE Reflex SRS computes the SRS from transients in the time domain in order to determine the damage potential of transient events.
Package testing and transport simulation testing are designed to simulate a product’s journey from when it is boxed at the factory until it reaches the customer. The primary purpose is to ensure that the packaging will sufficiently protect the product and that the packaging itself can withstand the stress of transportation. Tests are designed to reproduce the effects of transport on, for example, a pallet of boxed televisions, a transit-packaged washing machine or a crate of components for a vehicle or aeroplane. Tests can also be used to improve packaging design and to optimize packaging material use.
The suggested system for package testing combines an LDS V875-640 shaker fitted with a magnesium head expander with a LASERUSB controller and a SPA-K amplifier.
Environmental stress screening, also commonly referred to as temperature-controlled testing, or ‘shake and bake’, is a form of testing where products are subjected to high or low temperatures or to cyclical temperature fluctuation, while being shaken, to ensure that the combination of thermal and vibration stress does not cause the product to fail. It is a way of proving operational stability at extremes, such as desert conditions, hot manufacturing environments or very cold weather. Test types include highly accelerated lifetime testing (HALT) and highly accelerated stress screening (HASS). ESS is common for military products and components that often operate at extreme temperatures and for industrial products such as automotive components – both engine components and in-cabin assemblies. For military products, the testing temperature range is –55 °C to +125 °C. For industrial products, the common range is –40 °C to +85 °C.
To perform environmental stress testing, a shaker – for example, a V875 with a thermally-conditioned fixture and a thermal barrier – is fitted to an environmental chamber so that only the payload and the shaker fixture are inside the chamber. Depending on the type of test, the shaker can be in vertical or horizontal configuration. The LASERUSB controller supports standardized testing, including testing according to MIL-STD-810 and DEF STAN 00-35.
Consumer demand for improved quality and reliability has prompted automobile manufacturers worldwide to perform comprehensive testing for annoying noises. Buzz, squeak and rattle (BSR) testing ensures that automotive components and interiors remain durable and free from noise, for greater passenger comfort. Components and assemblies such as instrument panels, wing mirrors and vehicle interiors are tested. The OEMs and top-tier suppliers often strive to test as large assemblies as possible, up to 1/2 buck and 1/4 buck vehicle structures.
Depending on the payload under test, a typical system for BSR testing comprises of a V780 shaker with customized fixtures, for example, one for mounting a dashboard. In addition to the shaker system itself, array-based noise source identification and sound engineering technologies are necessary for in-depth detection, validation and improvements of squeak and rattle performance.
Qualification and acceptance testing (Q&A) ensures that equipment designs meet the performance expectations required for a particular mission – from assembly and transportation to launch and operation.
As satellite- and launcher-mission parameters vary widely, test parameters and configurations differ significantly. For example, with mechanical Q&A testing of satellites, standard qualification test procedures (QTP) are usually different from standard acceptance test procedures (ATP). The QTP is more comprehensive and is performed at higher levels on engineering models to qualify mechanical designs. It typically includes environmental testing such as vibration, shock and acoustic fatigue, and payloads can be either shaken to destruction or undergo non-destructive testing to assess their performance. The ATP, on the other hand, is a production test performed on the actual flight model to show that the structure meets performance specifications.
Qualification testing includes:
- Random and swept-sine vibration testing, which involves vibrating the satellite on a large LDS shaker, such as V994, in order to locate structural weaknesses and ensure that no significant structural dynamic changes have occurred
- Shock testing to simulate and analyze the (pyro-) shocks encountered during, for example, the separation and deployment of solar panels
The LASERUSB controller supports standardized testing, including testing according to MIL-STD-810 and DEF STAN 00-35