The close the forks are together, the greater the amount of stress and vice versa. Therefore, when pallets are stacked in blocks and the top surface of the underlying (bottom) load is uneven, the bottom deck boards will be subjected to a certain amount of stress.

A loaded pallet is subjected to higher static stresses
when it is supported in ordinary pallet racking or
drive-in stacking than when it is lifted by forked machines.

The relative magnitude of the bending moment
(ceteri paribus) and the stated conditions.

The forks of a pallet truck are normally spaced about 686mm apart and in some cases, allowance for narrower fork spacing of 533 mm, and assuming that the racking beams have a 75mm over-hang on each side.

The relative severity of the loading conditions resulting from the different types of support and that the bending moment, M, increases disproportionately with the size of the pallet.

The deck of the pallet must have the ability to withstand these bending moments without breaking or deflecting to an extend which puts the load in a precarious position.

Where a pallet has two decks, the load will be shared so that both decks contribute to the support and the blocks or feet of the pallet will have to bear compression loads, especially for block stacking.

In any particular situation, the actual stress that occurs in a pallet will depend very much on the nature of the load.

For example, a load consisting of bags of free flowing material such as rice will result in more stress than an equivalent load made up of large carton boxes.

Performance Criteria of pallets
The adoption of standard pallets is the pivotal point for
the standardization of the logistic chain in materials handling. Pallet should be able to resist prolonged exposure to moisture,  they have to be fire resistant.

As a general guideline, all pallet should be able to meet the following requirements:-

• it must be of adequate strength and carry the load it has been designed for in normal handling and storage processes.
   
• It must have adequate stiffness so that it can carry its load without deflecting to an unacceptable extent.
   
• It must be resilient enough to resist repeated abuse and accidental damage.
   
• The coefficient of friction of the deck must be high enough to prevent slippage of loaded goods. The coefficient of friction in the throat, when acting with the fork should also be high enough to prevent the forks from slipping.
   
• It should be sufficiently light to allow manual handling and its weight /strength ratio should be such that the pallet is not easily damaged when dropped.
   
• If it is durable, as opposed to expendable, the pallet should be designed for economic repair to an extent depending on the likelihood of its sustaining damage and the costs of repair.
   
• Certain industries call for hygienically clean pallets. For this purpose, the pallet in question should be easily cleaned for the particular purpose.
   
• Pallets are often required to be stored in the open or carried in open transport. In such instances, they should be able to resist the prolonged exposure to moisture and if used close to high temperature areas, like boilers, they have to be fire resistant.

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Although timber seems to be predominant material used in the fabrication of pallets... These four groups of materials may be sub-divided :-
1. Metals- steel, aluminum alloys
2. Plastics- injection molded, light weight formed or formed
3. Wood Products- cellular boards, clipboard pressing and plywood.
4. Composites- steel and timber, steel and plastic, plastic and timber,
    or glass fiber and plastic.