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MIL-STD 202G Shock Testing

This test determines the ability of component parts and subassemblies of electrical and electronic components to withstand shocks. These shocks may be expected as a result of rough handling, transportation and military operations during a life cycle. 

This test differs from other shock tests in that the design of the shock machine is not specified. However, the  half-sine and sawtooth shock pulse waveforms are specified with tolerances. The frequency response of the measuring system is also specified with tolerances.

Keystone Compliance is a military shock lab with significant MIL 202 shock and vibration lab testing experience. Our mechanical shock lab is perfect for all your shock compliance needs. We have a fully capable aerospace shock lab. Our test engineers have an in-depth knowledge of MIL-202G shock and MIL-202H shock testing. 

The following information is extremely technical in nature. It provides a summary of test method 213 shock (specified, as derived from the MIL-STD 202G shock section. Even though the language is from MIL-202G shock, it applies previous versions of the standard. This includes military standards like MIL-STD 202H shock.

What are the Effects of MIL-STD 202 Shock Testing on the Test Material? 

Mechanical shock may have adverse effects on the physical and functional integrity of the test materials. Generally, the damage potential is a function of the amplitude, velocity, and duration of the shock. Adverse effects on the materials overall integrity are magnified when shocks frequency content’s correspond with the material’s natural frequencies. 

The material’s response to the mechanical shock environment will, generally, be highly oscillatory. It will have a short duration, and a substantial initial rise time. It includes large positive and negative peak amplitudes. The peak responses of material to mechanical shock will, generally, be enveloped by a decreasing form of exponential function in time. 

Generally, mechanical shock applied to a complex multi-modal material system will cause the material to respond to two things. One, forced frequencies of a transient nature imposed on the material from the external excitation environment. Two, the material’s resonant natural frequencies either during or after application of the external excitation environment. 

Such a response could lead to several issues including:

  • Material failure, due to increased or decreased friction between parts, or general interference between parts.
  • Material failure due to cracks in fracturing crystals, ceramics, epoxies, or glass envelopes
  • Changes in material dielectric strength, loss of insulation resistance, and/or variations in magnetic and electrostatic field strength.
  • Low cycle fatigue, or accelerated fatiguing of materials. 
  • Permanent mechanical deformation of the material due to overstress of material structural and non-structural members.
  • Collapse of mechanical elements of the material due to the ultimate strength of the component being exceeded.
  • Potential piezoelectric activity of materials.
  • Materiel electronic circuit card malfunction, electronic circuit card damage, and electronic connector failure. Occasionally, circuit card contaminants that are able to cause short circuit are dislodged under material response to shock.

What Shock Pulses are Specified in MIL-202 Shock Testing? 

Two types of shock pulse are specified: a half-sine shock pulse and a sawtooth shock pulse. A sawtooth shock pulse is assumed to have a damage potential minimally as great as the half-sine pulse. This is for single degree of freedom systems. It is only true if the shock spectrum of the sawtooth pulse is minimally as great as the half-sine pulse. 

This condition exists for two such pulses of the same duration. This is if generally the acceleration peak value of the sawtooth pulse is 1.4x’s that of the half-sine pulse.

What is the Half-Sine Shock Pulse in Military shock Testing? 

The velocity change of the pulse shall be within ±10 percent of the velocity change of the desired shock pulse. The velocity change may be determined either by direct measurement, indirectly, or by integrating the area under the measured acceleration pulse. 

For half-sine acceleration pulses of less than 3 milliseconds duration the following tolerances should apply: 

The faired maximum value of the measured pulse shall be within ±20 percent of the specified ideal pulse amplitude. Its duration shall be within ±15 percent of the specified ideal pulse duration. The velocity change associated with the measured pulse shall be within ±10 percent of Vi = 2AD/π. 

The measured pulse will then be considered a nominal half-sine pulse. It will have a nominal amplitude and duration equal to respective values of the corresponding ideal half-sine pulse. 

The duration of the measured pulse shall be taken as Dm = D(.1A)/.94; where D(.1A) is the time between points at .1A for the faired measured acceleration pulse.

What is the Ideal Half-Sine Pulse for Proper Shock Testing?

The measured acceleration pulse must lie within the boundaries given by the broken lines. In addition, the actual velocity change of the shock must be within 10 percent of the ideal velocity change. The actual velocity change can be determined by direct measurements, or from the area under the measured acceleration curve. 

The ideal velocity change is equal to Vi = 2AD/π. A is the acceleration amplitude and D is the pulse duration of the ideal pulse.

What is the Sawtooth Shock Pulse According to Test Specifications?

The velocity change of the faired measured pulse shall be within ±10 percent of the velocity change of the ideal pulse.

What is the Ideal Terminal-Peak Sawtooth for Proper Shock Testing?

The measured acceleration pulse must be within the boundaries given by the broken lines. In addition, the actual velocity change of the shock pulse must be within 10 percent of the ideal value. The actual velocity change can be determined from direct measurements, or from the area under the measured acceleration curve. 

The ideal velocity change is equal to Vi = PD/2. P is the peak value of acceleration, and D is the pulse duration.

What Shock Laboratory Should You Trust? 

Looking to get a shock certification for your product? Contact Keystone Compliance today to work with an expert who understands the requirements of military and aerospace shock testing. Keystone has military and aerospace shock testing labs, functioning to the best shock testing for your product. Talk to our experts to develop a streamlined test plan and receive a professional and affordable quote. 

As an expert in shock certification, Keystone Compliance has been recognized as one of the best shock labs in the country. Our capabilities include testing to commercial and military shock testing standards. Contact us to learn why so many manufacturers rely on Keystone Compliance to meet their shock and vibration testing needs.

Looking for other MIL-STD-202 compliance tests? Click on a link below to learn more about the other test methods.