The large shock force generated by the impact comes from the change in momentum (mv) of the object in motion with the object being struck (e.g., hard ground) at the moment of very short contact (Δt), i.e.
F（Δt）=m(v1-v2)
or Amax==(v1-v2)/Δt
F—- impact force, kN
Δt—- impact contact time, i.e., pulse width D, ms, s
m—- mass of the object in motion, kg
Amax—- maximum acceleration of the impact, m/s2
v1, v2—- velocity of motion of the moving object before and after impact, m/s
The impact results in a large impact force (or acceleration) being applied to the product in a very short period of time, so that the response characteristics of the product to the external impact environment exhibit the following characteristics: high frequency oscillation, short duration, significant initial rise time and high magnitude of positive and negative peak acceleration.
For products with complex multimodal characteristics, the shock response consists of two frequency response components.
- The dynamic characteristic response component of the forcing given by the external excitation environment (shock force) applied to the product.
- The response component generated by the product according to its own inherent dynamic characteristics during or after the application of the excitation.
These responses will inevitably have a negative impact on the structural integrity of the product, functional indicators and performance parameters of internal components, and the degree of impact varies with the level and duration of the shock. In particular, when the impact duration and the inverse of the product’s inherent frequency, or the input shock environment of the main frequency components and the product’s inherent frequency, will strengthen and aggravate the external shock on the product structure and functional integrity of the degree of impact. This is manifested by:
- Product failure caused by increased or reduced friction between parts, or mutual interference.
- Product insulation strength changes, electrical insulation impedance decline, magnetic and electrostatic field strength changes.
- Product circuit board failure, damage and electrical connector failure.
- The product may cause a short circuit by displacing the excess material on the circuit board under the effect of shock.
- Permanent mechanical deformation of the product due to overstress of the structural or non-structural parts of the product.
- Damage to the mechanical parts of the product due to exceeding the ultimate strength.
- Accelerated material fatigue (low circumferential fatigue).
- Potential piezoelectric effect of the product.
- Product failure due to rupture of crystal, ceramic, epoxy or glass packages, etc.