MIL-STD-810G covers shock in Method 516.6. Shock is an infrequent single pulse acceleration with a narrow pulse width imparted to a device. Method 516.6 is one of the more complicated Methods comprised of 38 pages. In addition there are three Annexes:
Annex A – Statistical Considerations (8 pages)
Annex B – Effective Shock Duration (4 pages)
Annex C – Autospectral Density (4 pages)
Method 516.5 is one of the more widely performed Methods, often in conjunction with Method 514.6 (Vibration).
Shock tests are performed to:
- provide a degree of confidence that material can physically and functionally withstand the relatively infrequent, non-repetitive shocks encountered in handling, transportation, and service environments. This may include an assessment of the overall material system integrity for safety purposes in any one or all of the handling, transportation, and service environments;
- determine the material’s fragility level, in order that packaging may be designed to protect the material’s physical and functional integrity; and
- test the strength of devices that attach material to platforms that can crash.
A shock environment is generally limited to a frequency range not to exceed 10,000 Hz, and a time duration of not more than 1.0 second. (In most cases of mechanical shock the significant material response frequencies will not exceed 4,000 Hz and the duration of material response will not exceed 0.1 second.) The material response will, in most cases, be highly oscillatory, of short duration, with a substantial initial rise time with large positive and negative peak amplitudes.
Shock is the term applied to a comparatively short time (usually much less than the period of the fundamental frequency of the material) and moderately high level (above even extreme vibration levels) force impulse applied as an input to the material.
Failure modes to shock events include:
- material failure as a result of increased or decreased friction between parts, or general interference between parts;
- changes in material dielectric strength, loss of insulation resistance, variations in magnetic and electrostatic field strength;
- material electronic circuit card malfunction, electronic circuit card damage, and electronic connector failure. (On occasion, circuit card contaminants having the potential to cause short circuit may be dislodged under material response to shock.);
- permanent mechanical deformation of the material as a result of overstress of material structural and non-structural members;
- collapse of mechanical elements of the material as a result of the ultimate strength of the component being exceeded;
- accelerated fatiguing of materials (low cycle fatigue);
- potential piezoelectric activity of materials, and
- material failure as a result of cracks in fracturing crystals, ceramics, epoxies, or glass envelopes.
Method 516.6 includes eight procedures:
Procedure I – Functional Shock
Intended to test material (including mechanical, electrical, hydraulic, and electronic) in its functional mode (as installed in the field) and to assess the physical integrity, continuity and functionality of the material to shock.
Procedure II – Material to be packaged
The intent of this test is to ensure the functionality of materiel after it has been inadvertently dropped before, during, or after a packaging process.
Procedure III – Fragility
Used to determine a material’s ruggedness or fragility so that packaging can be designed for the material, or so the material can be redesigned to meet transportation and/or handling requirements. This test is designed to build up in severity until a test item failure occurs, or a predetermined goal is reached.
Procedure IV – Transit Drop
Intended for material either outside of or within its transit or combination case, or as prepared for field use (carried to a combat situation by man, truck, rail, etc.).
Procedure V – Crash Hazard Shock Test
Intended for material mounted in air or ground vehicles that could break loose from its mounts, tiedowns or containment configuration during a crash and present a hazard to vehicle occupants and bystanders.
Procedure VI – Bench Handling
Intended for material that may typically experience bench handling, bench maintenance, or packaging.
Procedure VII – Pendulum Impact
Intended to test the ability of large shipping containers to resist horizontal impacts, and to determine the ability of the packaging and packing methods to provide protection to the contents when the container is impacted.
Procedure VIII – Catapult Launch/Arrested Landing.
Intended for material mounted in or on fixed-wing aircraft that are subject to catapult launches and arrested landings.