Mechanical Shakers  | Shock Machines  |  Fixtures |  Test Lab


Mechanical Shakers

Q1 May a mechanical shaker perform a constant acceleration sweep?
A1 No, mechanical shakers may perform a constant displacement sweep. As frequency increases, displacement will remain the same and acceleration will increase as demonstrated by the formula; g = .0511(d)(f)(f), where

g = acceleration, g
d = displacement, inches p-p
f = frequency, Hz

Q2 May a mechanical shaker perform ESS?
A2 Yes! A most popular use for mechanical shakers is to weed out manufacturing defects, such as excess solder and loose screws, during production. This process is called Environmental Stress Screening (ESS) where the product is stimulated, as opposed to simulated. In this regard, it is intended to ultimately build product from component to finished product with zero defects. The prevailing philosophy for the success of the mechanical shaker for ESS application is that the shaker, in all probability, has enough performance (force, displacement, acceleration) to damage product. If the shaker is capable of inducing failure and all aspects of the shaker are adjustable, (which they are!), then there may be a lesser vibration level in which manufacturing defects will occur.

Q3 My product worked fine before we shipped. When it got to the end destination, it no longer worked. Clearly, something happened during transportation. I must need a Transportation Simulator?
A3 Not necessarily. The Transportation Simulator is intended to qualify the package AND the enclosed product to insure that they, together, can withstand the rigors of transportation. The materials placed inside the package are intended to attenuate, or lessen, the potential harmful accelerations which may been countered. It is possible that the materials could amplify, or increase, the accelerations present. But what have you done to demonstrate that the product had any reliability prior to shipment? What real evidence is there that shows that transportation is the culprit? The product should, first, undergo, its own vibration screen as explained in A2. Only upon demonstrating that the product is robust, can we determine that transportation is the source of failure.


Shock Machines

Q1 What is the maximum acceleration that can be generated?
A1 Shock Machine capability is rated in terms of VELOCITY. The formula for calculating the velocity change for a half-sine pulse is:

V = Velocity Change (in/sec)
g = acceleration (g)
t = time (seconds)

Maximum acceleration, then, is dependent upon the velocity change capability of the machine and the time duration required for the pulse.

Q2 What is meant by the term half-sine programmer?
A2 Each half-sine pulse time duration requires a separate programmer which must be manually situated between the underside of the shock carriage and the machine base. A programmer is simply the term used for the pad, generally an elastomer, which allows the carriage to rebound to create a half-sine shape with a given time duration.

Q3 Why do you recommend the use of a mousetrap amplifier?
A3 The Mousetrap Shock Amplifier is used for two primary purposes. First, as an amplifier to produce increased velocities. Second, because the Mousetrap Amplifier is supported on springs, the springs act as a "mechanical filter" which serve to reduce the ringing associated with short time duration pulses. We define short time duration as any pulse less than 3 ms.


Fixtures

Q1 Why do you use washers?
A1 All bolts must have steel washers placed under their heads to prevent gouging the material and to prevent any separation between the fixture and the test apparatus. Separation will cause unwanted dynamics and cause data to be flawed.

Q2 Can you tell me about damping?
A2 Magnesium is soft, so, it offers natural inherent damping. Much more so than aluminum or steel. If damping is required, M/RAD would utilize a visco-elastic material adhered to the sides of the fixture or foam, placed in cavities, to minimize the amplification factor associated with a resonant frequency. A Q of 40 - 50 is typical WITHOUT the Damping Material. A Q of 20 - 25 is typical WITH the Damping Material. Note that the Damping Material does not eliminate the natural frequency, rather it serves to reduce the amplification factor. It may still be necessary to use multi-point averaging or notching to control the fixture to required tolerance limits, if applicable.

Q3 Can you tell me about inserts?
A3 As magnesium is soft, it requires a steel insert. Otherwise, bolts and fasteners will simply strip from the fixture.

Q4 Can you tell me about corrosion protection?
A4 Especially when placed inside an environmental chamber, a fixture can corrode. The method most commonly used to protect magnesium is HAE per MIL-M-45202C, Class A which ultimately produces a tan coating and is an excellent paint base.


Test Lab

Q1 What tests can you perform?
A1 Note the following;

• Classical Shock; half-sine, sawtooth, square wave
• Shock Spectrum
• Vibration; sine/swept sine and random
• Drop Test per ISTA, ASTM and MIL-STD
• Bounce Test per ISTA, ASTM and MIL-STD
• Shock Test per ISTA, ASTM and MIL-STD

Q2 What equipment is in the lab?
A2 Note the following;

VIBRATION

MB C10 ED Shaker
F; 900 lbs

Thermotron DS640 ED Shaker with 36 in x 36 in sliptable
F: 6,000 lbs

Thermotron DS640 ED Shaker with 36 in x 36 in head expander
F: 6,000 lbs

M/RAD Model 3030(500)V, 211 Mechanical Shaker
F: 6,400 lbs

M/RAD Model 3636(200)E, 611 Mechanical Shaker
F: 2,000 lbs

Thermotron 4 Channel Controller
Sine, swept-sine, random and shock

M/RAD Model WIN491 Sweep Controller

M/RAD Model WIN437 Vibration Monitor

SHOCK

M/RAD 0909(50)PA-MP, Pneumatic Shock Machine

M/RAD SRA-1200-4, 4 Channel Instrument
M/RAD SRA-1400-4, 4 Channel Instrument

PACKAGE TESTING

M/RAD Model 4848(500)TS, Transportation Simulator

M/RAD Model 3636(200)DT, Drop Tester

Q3 May the equipment in the lab be sold?
A3 Yes, except for the ED Shakers