Shock testing with long durations can be a challenging endeavor. DES recently had to perform a 35G peak, half sine shock with a 50 millisecond duration. The video below shows this shock test being performed.
This sounds like an easy shock to carry out because a peak of 35G is low compared to many shocks. However, this is a difficult shock to perform because 50 milliseconds is a long duration. Most typical shock durations are less than 20 milliseconds.
A half sine shock impulse has the shape of a half sine wave. More details can be found elsewhere on our blog, in an article titled “Classical Shock Testing“.
Continue reading Shock Testing: Long Duration Half Sine Shock →
Temperature cycling testing is another method of accelerated life testing for products that are exposed to temperature variations during use in normal operation. The temperature variations can be a result of self heating for products that are repeatedly turned on and off, or can be the result of cyclic environmental changes — such as temperature variations from day to night — or other causes.
These repeated temperature changes can result in thermal fatigue and lead to eventual failure after many thermal cycles. Accelerated life testing can be performed by cycling the product to high and low temperatures that exceed its normal use temperatures.
It should be noted that temperature cycling may also be referred to as thermal cycling or thermal shock testing. However, some test standards, such as MIL-STD-883, make the distinction between temperature cycling being performed as air to air testing and thermal shock being performed with the samples transferred between liquids. This article deals with testing performed using an air to air thermal cycle chamber.
Typical temperature cycling equipment consists of at least one hot chamber and one cold chamber. The test samples are automatically transferred between the two chambers by an elevator-type mechanism. It is also possible to perform temperature cycling in a single compartment chamber where the temperature is ramped between hot and cold. This generally produces a slower rate of temperature change compared to the two chamber method.
Continue reading Temperature Cycling Testing: Coffin-Manson Equation →
First we should answer, what is a pyroshock or a pyrotechnic shock? Both pyroshocks and pyrotechnic shocks are the same thing. A pyroshock occurs when explosive events are used to separate the stages of rockets or missiles, or from a ballistic impact to a structure by a projectile. When a pyroshock occurs, a stress or shock wave propagates through the structure and into the electronic equipment contained within the structure.
Pyroshocks are unique shocks that have high G-level, high frequency content with very little velocity and displacement change during the shock. The frequency range of a pyroshock is usually 100 Hz to 10,000 Hz or greater. Pyroshocks have a very short duration of usually less than 20 milliseconds. The acceleration time history of a pyroshock approximates a combination of decaying sinusoids as shown in Figure 1.
Speeding up the process of device or circuit failure requires extreme inputs, those that are unlikely to occur during real-world use by customers regardless of the environment. Three common testing inputs are high and low temperatures, rapid cycling of the same and vibration along six-axes. In some cases, a highly accelerated life test (HALT) will incorporate combined temperature and vibration stresses. These inputs can result in component failure in the span of days, hours, or even minutes compared to months or years of typical usage.
While the percentages of failure based on the stress applied to a product can vary significantly, highly accelerated life testing can typically expose weaknesses faster than other means of testing. For example, of the above inputs, roughly two-thirds of failures will only come after the introduction of vibration alone or combined vibration and temperature tests. This means that during the product development process, a significant number of potential flaws would not be identified through testing that did not include these two stresses.
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Real world vibrations are usually of the random type. Vibrations from automobiles, aircraft, rockets are all random. A random vibration test can be correlated to a service life if the field vibrations are known. Since random vibration contains all frequencies simultaneously, all product resonances will be excited together which could be worse than exciting them individually as in sine testing. Sometimes random vibrations are mixed with sine vibrations in Sine-on-Random Vibration Testing. Also, a low level of broad band random vibration can be mixed with additional high levels of narrow band random vibrations in Random-on-Random Vibration Testing.
Some common test standards that have specifications for Random Vibration Testing are:
The most common types of vibration testing services conducted by vibration test labs are Sinusoidal and Random. This primer is an explanation of the typical requirements found in vibration test specifications and the parameters used to control the vibration tests. Both types of vibration tests are used to evaluate products for ruggedness, durability and to expose vibration defects.
Product reliability is essential to success in today’s competitive global market. HALT and HASS are intensive methods used to expose and then improve design and process weaknesses. HALT and HASS are faster, less expensive and more accurate than traditional testing techniques. HALT and HASS are proven processes used to lower product development and manufacturing costs, compress time to market, reduce warranty costs, improve customer satisfaction, gain market share and increase profits. Some companies have reported savings in the millions after using HALT and HASS.
HALT and HASS can accelerate a product’s aging process from actual months into test minutes much faster than traditional testing!
Continue reading An Informational Guide to HALT and HASS →