A vast amount of goods and products are transported in bulk as palletized unit loads, where the pallet is the base of the unit load. Material handling systems represent the physical environment in which unit loads are transported through supply chains. Material handling systems include different transportation modes and storage conditions, many of which are well researched. While industrial forklifts are paramount to material handling systems, the physical effect they have on load systems is not well understood. The weight of the unit load causes the pallets to deflect, and previous research has revealed that forklift vibration amplifies pallet deflection. The effects of forklift vibration on pallet deflection are not considered in international standards used to determine pallet load capacities. Standards such as ISO 8611 and ASTM D1185 provide deflection limits that are used to determine pallet load capacities, yet there is a lack of understanding and justification on these deflection limits related to forklift support conditions. A comprehensive understanding of the effects of forklift vibration on unit load performance is necessary to produce accurate and safe load capacity ratings. In this research, two studies were completed to gain further understanding on unit load performance and stability in forklift handling conditions. The first study evaluated pallet deflection and unit load stability of unbound unit loads designed with a 20 mm. performance limit (ISO 8611, 2011). Common forklift handling factors were investigated and included fork tine angle (level and 4-degree incline) and pallet orientation (racked across the width and across the length). The results showed that the dynamic environment of forklift handling created unstable unit loads. The second study of this research project investigated unit load performance against unit load design factors of load capacity (500 lbs., 750 lbs., 900 lbs.) and box size (8 in., 12 in., 16 in.). The results showed that unit load instability occurred at all load levels and all box sizes. Additionally, an increase in box size decreased load bridging for unit loads under fork tine support conditions. Furthermore, the time to instability was used to calculate projected forklift travel distances that can be used to further optimize material handling systems. / Master of Science / Many goods and products are transported across the world every day using a multitude of transportation modes and systems. The use of pallets to transport goods in bulk optimizes efficiency of the supply chain system. The physical transportation environment pallets are exposed to is used to determine their load capacity. While pallets are commonly handled by industrial forklifts, the environment the forklift creates for the pallet is not well understood. The mechanical stressors that forklifts create play a vital role in pallet performance and have been found to cause unit load instability.  Vibration represents one mechanical stressor that creates a hazard for material handling.  The goal of this research was to evaluate the performance of pallets in relation to the vibration imposed by industrial forklifts.   Previous studies measured forklift vibration and developed test procedures to replicate the forklift handling environment in a laboratory setting. Previous research investigated unit load performance where the pallet load capacity was determined using a 4.5-degree performance limit (ISO 8611, 2021). This study expanded on previous research by further investigating unit load performance against various load capacities and design parameters. This study included two experiments. The first experiment investigated the effect of common material handling factors on unit loads designed with a 20 mm. performance limit (ISO 8611, 2011). The second experiment investigated the effect of unit load design parameters such as load capacity and box size on unit load performance.   This study found that forklift vibration creates a hazardous environment where pallet deflection combined with magnified vibration caused unbound unit loads to become unstable. The data also revealed that larger boxes decrease unit load bridging in the fork tine support condition. Additionally, projected forklift travel distances were determined for various pallet testing standards. This data can be used to further optimize material handling systems.

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To achieve goal-orientated behaviour, selective attention is often needed to filter out irrelevant information. Past research has shown that working memory (WM) plays a critical role in selective attention, with high WM load leading to more distractor interference than low WM load. However, because WM load is usually manipulated by requiring participants to hold in memory either one or several digits that were presented simultaneously while performing a selective attention task, the extent of attentional focus was not controlled. The present study examined the effect of WM load on distractor inhibition while keeping attentional focus constant by presenting one digit (low load condition) or six digits (high load condition) sequentially. The participants in the high-load condition demonstrated greater distractor interference than the participants in the low-load condition, suggesting that WM load influences distractor inhibition even when the extent of attentional focus was controlled. This result provides converging evidence to Lavie's (1995, 2005) load theory of attention and cognitive control.

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