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Common Packaging Terms
Common Terms Used in Protective Package Design and Testing
A vector quantity describing the change of position of a body and usually measured from a position of rest.
The rate at which displacement changes; it is a vector quantity with both magnitude and direction. It is the differential of displacement with respect to time. It is also the integral of acceleration.
the rate at which velocity changes. It is the differential of velocity with respect to time. The acceleration of gravity (g) is a constant (386 in/sec) or (9.8 m/s). Impacts are normally measured in multiples of Earth's gravitational constant (G's).
the difference between impact and rebound velocity (Vi – Vr). This quantity can be thought of as the change in momentum associated with a given impact event. The difference in system velocity magnitude and direction from the start to the end of a shock pulse.
is also directly related to an impact drop height by the following equation:
ΔV = (1 + e)√(2gh)
where: e = the coefficient of restitution of the impact services (V
g = Earth's gravitational constant (386 in/s or 9.8 m/s)
h = drop height
is also equal to the area under the acceleration versus time pulse from a monitored impact event, that is, the magnitude may be determined from the integral of the acceleration versus time signature.
The oscillation of an element of a mechanical system about a fixed reference point.
A sudden, severe, non-periodic excitation of an object or system.
A vibration consisting of a wave form that is repeated at equal time intervals.
An oscillation having an instantaneous frequency and amplitude that can be specified only on a probability basis.
Simple Harmonic Motion:
Periodic vibration that is a sinusoidal function of time.
A complete sequence of values of a periodic quantity occurring over a definite time period.
Smallest interval of time in which a reoccurring event repeats itself.
The reciprocal of the period necessary for one complete oscillation. This is often described in cycles per second or "Hertz" abbreviated Hz.
the frequency of excitation.
the frequency of free oscillation of a spring/mass system.
the frequency at which a spring/mass system displays its maximum response.
a sinusoidal quantity having a frequency that is an integer multiple of a fundamental or natural frequency.
resonance of a system in forced vibration exist when any change, however small, in the frequency of excitation causes a decrease in the response of the system. Resonance represents a maximum of response of a spring/mass system to forced vibration input.
the dissipation of oscillatory or vibratory energy with motion or with time.
is the minimum viscous damping that will allow a displaced system to return to its initial position without oscillation.
Single Degree of Freedom System:
a system consisting of a rigid mass attached to a referenced foundation by a mass-less spring that is constrained along a straight line.
a plot of the maximum response experienced by a single degree of freedom system as a function of its own natural frequency in response to an applied shock input. The response may be expressed in terms of acceleration, velocity, or displacement.
a substantial disturbance characterized by a rise in BK and acceleration from a constant value in a short period of time. Shock pulses are normally displayed graphically as curves of acceleration as a function of time.