Search

Glossary

See also the abbreviations and symbols.

Acceleration
A vector quantity (having magnitude and direction) that specifies the rate of change of velocity.
Allowance
A space between the cushioning material and the object or container that enables the package components to be easily assembled and promotes effective cushion performance by avoiding binding or excessive friction.
Bubble pack
Two layers of polyethylene film, one of which is embossed with circular cells forming an air-encapsulated cushioning material.
Buckling
Uneven compression or falling over of a pad of insufficient bearing area. The minimum bearing area of a pad is (1.33 x material thickness).
CAD
Acronym for Computer Assisted Design.
Cellulose wadding
A wood fibre product, generally most effective as a wrapping material but can also be used for cushioning; it is not recommended for highly fragile items.
Convoluted
Convoluted foam has a surface with cone-shaped projections that provide high loading of the material under static conditions and a progressive increase in the area of foam in contact with the protected item on impact. It is mainly used for lightweight, fragile items. Convolutions are described in terms of the overall thickness, pitch, and valley of a sectional view of the material. For example, convoluted foam materials M9 and M11 have the following form: overall thickness, 5.3 cm (2.1 in); pitch, 3.5 cm (1.38 in); valley, 2.2 cm (0.88 in); and materials M8 and M10 have the form: overall thickness, 2.5 cm (1 in); pitch, 3.5 cm (1.38 in); valley, 1.0 cm (0.42 in).
Creep
The progressive loss of material thickness over time. [A permanent “set” of 10–15% can be expected when most foam cushioning materials are loaded within their normal load range; if a material is overloaded, excessive loss in thickness will result, leading to looseness inside a package and a loss of cushioning effectiveness.]
Damping
A general term for all the forces that can dissipate shock or vibration energy; two examples of damping forces are friction and air resistance.
Depth
The shorter horizontal dimension of an object when in its preferred transit orientation.
Design drop height
The drop height that has been used by PadCAD for the design of a given cushioning system, and the drop height for which the reported shock performance specifications are valid.
Design screen
PadCAD’s main data input screen on which all of the parameters of a cushioning problem are entered.
Dimensional weight
A quantity used by shippers to measure package density when estimating shipping costs; the dimensional weight is calculated by multiplying the object’s height, width, and depth, and dividing this product by some denominator value specific to the shipper.
Drop height
The height above a hard floor surface from which a package might be dropped during the handling phases of shipment (when most shipping damage occurs); drops can be accidental in nature or the result of mishandling.
Dynamic cushioning curve
A graph of peak acceleration versus static load that summarizes the shock isolation performance of a cushioning material; a separate graph is produced for each different drop height, and each curve on the graph corresponds to a different cushioning material thickness.
Equivalent shock frequency (F.eq.)
The natural frequency of an object on a protective cushioning system.
Fixed drop height
A worst-case hazard [e.g. a drop of approximately 75 cm (30 in) from a truck tailgate] that can be assigned to packages containing fragile items. [A high fixed drop height will normally be assigned to items of high value; a low fixed drop height can be specified for packages that contain items of low value, or for packages that contain items of moderate value that are shipped through distribution networks that have lower risk levels (e.g. works of art or commercial items transported by specialized handlers).]
Flexible element
A vibration-prone component of an object. [Flexible elements may attenuate or amplify externally applied shocks and vibration depending on their frequency and the properties of the cushioning system; the two key items that describe the vulnerability of a flexible item are natural frequency and the fraction of critical damping.]
Fraction of critical damping
The amount of damping that is present in an object relative to a critical value that causes the object to return to its equilibrium position without oscillation when it is displaced from its equilibrium position and released.
Fragility
A measure of the sensitivity of an item to shock which is expressed in units of G (multiples of the force due to gravity); the lower the G rating, the more sensitive an item will be to shock.
G
Ratio of the force of impact to the force due to gravity; used to express shock severity and object fragility.
Height
The vertical dimension of an object when in its preferred transit orientation.
Insulation
Material added to the interior surfaces of a shipping container to increase the time it takes for the package to respond to external changes in temperature during shipment.
Maximum deflection (dm)
The maximum distance that an object will deflect into the protective cushioning system along an axis perpendicular to the indicated surface (Front, Right, Top) when the package is dropped flat onto that surface from the design drop height.
Pad coverage
The amount of cushioning material that covers the available surface area of the object to be packed.
Peak acceleration of the cushioned object (Go)
The maximum shock (in units of G) experienced by a cushioned object (as a rigid item) when the package is dropped flat on the Front (or Back), Right (or Left), and Top (or Bottom) surfaces from the design drop height.
Peak acceleration of flexible elements (Ge)
The product of the peak acceleration of the cushioned object (Go) and the shock amplification factor (Am) of a flexible element.
Polyethylene (PE)
An inert thermoplastic cushioning material with a closed cell structure.
Polystyrene (PS)
Non-elastic cushioning (or insulating) material that deforms permanently on impact.
Polyurethane (PU)
A soft open-celled material that is available as either an ester type or ether type (the ester formulation is more chemically stable than the ether type); this material must never come in direct contact with metals.
Probable drop height
A drop height assigned to a range of package weights that is used to estimate the handling hazards of loading, unloading, and cargo transfer during shipment. Probable drop heights are summarized in tables and have evolved from observations, experience, and monitored shipments in the packaging industry.
Projections
Items that extend from the surfaces of an object (e.g. control knobs on electronic equipment) into the sway space (space between the external object surface and the inner container surface).
Resonance
The frequency of an externally applied source of vibration corresponds to the natural frequency of a flexible object; the resulting amplitude of vibration can sometimes reach levels that exceed the externally applied vibration source, and result in damage to the object. [The amount of vibration amplification that takes place depends on the external vibration frequency and the amount of damping that is present in the vibrating object to dissipate vibration energy; the greater the amount of damping, the lower the degree of vibration amplification.]
Road case
A general term for custom-made cases fabricated with plywood composite panels (e.g. aluminum or vinyl laminates) and held together with special aluminum extrusions and pop rivets.
Shock
A sudden, severe disturbance of a mechanical system that causes it to respond with large relative displacement of its components.
Shock amplification factor (Am)
A dynamic effect in a flexible component that is a function of the ratio of the component frequency and equivalent shock frequency; the applied shock may be attenuated or magnified to a maximum level of 1.8 times greater than the applied shock (the amount of magnification depends on the natural frequency of the flexible component and its fraction of critical damping). PadCAD evaluates the shock amplification factor using a theoretical model based on a half sinusoidal shock motion for five different fractions of critical damping values: 0, 0.05, 0.20, 0.50, and 1.00.
Shock pulse
A shock pulse is characterized by its duration, intensity, and shape (appearance on a graph of intensity versus time).
Shock pulse duration (T)
The time during which the acceleration is above a pre-defined fraction of the maximum shock pulse amplitude; shock pulse duration is independent of drop height.
Static load
The load per unit area applied to a cushioning material under static conditions; static load is normally expressed in kilograms per square centimetre or pounds per square inch.
Sway space
The clearance between the outer surface of a packaged object and the inner surface of the shipping container in which the packaged item will move in order to dissipate shock and vibration energy; the sway space may either be filled with cushion material or be partially open (as in the case of pad solutions).
Thermal half time
The time it takes for a package to reach a new temperature that is halfway between its current equilibrium temperature and the temperature of a new environment to which it is suddenly exposed.
Transmissibility
A non-dimensional ratio of the vibration response of a system to the amplitude that causes the motion under steady-state conditions.
Triwall
Triple-wall corrugated cardboard, 1.6 cm (5/8 in) thick.
Void fill
Foam that extends beyond the surface of an object to fill in voids, such as corners, inside the sway space of the package.
Weight
The total weight supported by a cushioning system, including the weight of the fragile object plus the weight of any support frames or inner containers that are used.
Width
The longer horizontal dimension of an object when in its preferred transit orientation.

Abbreviations and symbols

a:
linear dimension used in design (cushion design parameter)
b:
linear dimension used in design (cushion design parameter)
n:
umber of additional support pads. If n=0, then no support pads will be added to the layout.
A:
pad area
cm:
centimetre
Con.:
convoluted
ft:
foot
G:
force of impact expressed as a multiple of the force due to gravity
h:
hour
Hz:
hertz (cycles per second)
in:
inch
kg:
kilogram
kPa:
kilo pascal, where the pascal is the International System Unit (SI) derived unit of pressure used to quantify internal pressure. It is defined as one newton per square metre.
lb:
pound
m:
metre
psi:
pound per square inch or, more accurately, pound-force per square inch is a unit of pressure resulting from a force of one pound-force applied to an area of one square inch.
PE:
polyethylene
PS:
polystyrene
PU:
polyurethane
Q:
vibration transmissibility
XLPE:
cross-linked polyethylene
Date modified: