No description available.

The primary objective of this study was to quantitatively analyze compressive static stress distributions across pallet deck surfaces supporting flexible and rigid packaging in simulated warehouse storage systems. Three different densities of polyolefin foams (2, 4, and 6 lb/ft3, pcf) simulated a variety of flexible and rigid packaging with a range of stiffness properties. A layer of single wall C-flute corrugated fiberboard acted as a sensing medium and also simulated the bottom of a corrugated box. Pressure sensitive films were used to detect compressive static stresses at the interface between the polyolefin foams and the pallet deckboard. Image analysis computer software program was developed to quantitatively characterize stress distributions left on pressure sensitive film. 280 lbs of compression load were applied to a Plexiglas® pallet section (40 x 3.5 inches, L x W) with ¾ inch deck thickness, as well as to a steel pallet section (40 x 3.5 inches, L x W) with ½ inch deck thickness. In both cases, the pallet sections were used in a simulated pallet storage rack. 700 lbs of compression load were applied to the same steel pallet section that was used in the racking simulation and the Plexiglas® pallet sections (40 x 3.5 inches, L x W) with ½ and ¾ inch deck thicknesses were used in simulated block (floor) stack storage to measure the stress distributions and deflections of deckboards. Applying the final models of resultant non-uniform stress distributions enabled the development of finite element analysis (FEA) models of pallet deckboard deflections. The predicted FEA models of the deckboard deflections were validated through comparison with experimentally measured deflections in the simulated warehouse storage systems. In the final models, the resultant three foams' stress distributions across pallet deck surfaces in both rack and floor stack storage simulations were non-uniform. The changes in the degree of stress concentrations and maximum stress levels along the deckboards varied, depending on the stiffness of the foams and deckboards and the support conditions in the simulated warehouse storage models. Qualified test indicates that the 2pcf and 4pcf foams represent non-rigid sack products and the 6pcf foam represents rigid packaging and contents. All tests were conducted within a few minutes; hence, all test data were assumed to be initially resulted compressive stresses. The compressive stresses may change over time. The measure of stress concentrations is the stress intensity factor, which is the ratio of initial maximum resultant compressive stress to the applied stress. The initial maximum resultant compressive stresses were adjusted for rate of loading which varied due to the difference in the stiffness of the foams. The table below shows the adjusted initial maximum resultant compressive stress intensity factors. The product of the calculation uniformly distributed compressive stress and the stress intensity factor is the appropriate criteria for designing packaging of product with adequate compressive strength. These factors will be useful when designing pallets, packaging, and unit loads.In simulated block stack storage, the foam stiffness (package and product stiffness) had a more significant effect on the stress distributions and concentrations along the deckboards than did the pallet deck stiffness. As a result, the stiffer foam presented a greater change in stress levels along the deckboard under the compression load. The quantified and evaluated stress concentrations and stress distributions will be useful in understanding the interactions between pallets and packaging, reducing product damage and improving the safety of the work place during the long-term storage of the unit loads. The predicted FEA models will allow the industry to better optimize pallets, packaging, and unit load designs. / Master of Science

M.S.

With increased use of pallets constructed utilizing structural panel decks, there is a need for a standardized, reliability-based design system, PDS-PANEL, to assist in the design and manufacture of panel-deck pallets. The primary objective of this research was to develop finite element models which predict the static bending behavior of pallets with at least one panel deck. stringer and block pallets were modeled using plate elements to simulate deck behavior and were validated by comparing predicted deflections to experimentally measured deflections. Differences were considerably less than the allowable 15 percent for both stringer and block models. Sensitivity studies conducted with these models provided a rational basis to simplify models for use in the existing PDS-PANEL program developed at Virginia Polytechnic Institute & State University. Simplified models were required to have solution times of less than 2 minutes on a 286 type or more powerful personal computer (PC). / Ph. D.

An evaluation was made of the performance of 48 11 x 63 11 , reversible, doubleface, wing-type, two-way entry, nailed red-oak, stevedore pallets of two designs assembled with four different nails. Special consideration was given to Brazilian situations in the light of the interest of the author in the industrial potential of Brazil. The pallets of improved design had their top and bottom leading-edge deckboards backed up by follow-up deckboards. Furthermore, four nails, instead of three, were used for fastening the leading-edge deckboards and three nai Is, instead of two, were used for fastening the inner deckboards to each stringer. The sequence of tests on each pallet started with the initial stiffness test, followed by the rigidity test, the impact-incline deckboard-stringer separation test, and the follow-up static stiff,!'1ess and load-carrying capacity tests. The pallets of improved design were better than those of conventional design during all tests performed. The influence of the nails on pallet performance was significantly different only during the performance of the rigidity and impact-incline tests. During the latter test, the pallets of improved design assembled with 311 helically threaded hardened-steel nails were, on the average, 66 times better than the conventional pallets assembled with the Brazilian 2 ½” helically fluted nails. Recommendations were advanced, suggesting that the study be continued and that special consideration be given to the wood species available in Brazil for pallet assembly, to the use of improved nails, and to the environmental conditions under which stevedore pallets are exposed. / Master of Science

The Pallet Design System (PDS) is a widely accepted engineering procedure for comparing the performance of competing pallet designs. As part of a new version of the PDS, the objective of this study was to develop a durability model for pallets with structural panel decking. An accelerated rough material handling test system, "the VPI unit-load material handling FasTrack" , was developed to simulate pallets used in the unit-load material handling environments. 100 pallets representing 14 different designs were tested in the "FasTrack." Damages to these pallets were recorded after each test cycle. A procedure relating damage to repair cost was developed. The effect of panel-deck pallet design on the resistance to damage was evaluated in terms of the total number of damaged parts and average damage cost or repair cost. Test results indicate that panel grade and type, species of related wood parts, size of stringer and deckboards, joints, and pallet configurations affect the resistance of panel deck pallet to damage. The plots of average total damage cost, Cu adjusted for repair as a function of test cycle, U, fit the equation: Ct = aU - 1. The equation provided good fits to all the pallet designs tested. Using the initial purchase prices, the average cost and the economic life were calculated for all the pallet designs. The VPI "FasTrack" was calibrated based on the number of physical handlings and the amortized life. Three typical in-field handling environments were compared with the VPI "FasTrack". It concluded that the 30-cycle test period in the VPI "FasTrack" simulates between 2 to 5 years of field uses depending on the field handling system being simulated. Thirty Canadian Pallet Council (CPC) pallets with known 7 years of amortized life in the field were tested in the VPI "FasTrack". The 30-cycle test in the VPI system simulated 6 years of use in the similar handling environment of the CPC pallet used by the grocery industry in Canada. The average total damage costs for different pallet designs were related to pallet structural characteristics using multivariate regression analysis. The shear resistance through the thickness of the top panel deck, bottom deck flexural strength, pallet flexural strength, fastener withdrawal resistance, and pallet configuration were used to predict the total damage cost. A multiple regression model was developed. The model was verified by comparing the predicted values with the tested values of 12 panel deck pallets representing 2 designs. The results indicated that the model is reliable for the future predictions. / Master of Science

Pallet repair and reinforcement with metal connector plates (MCPs) may reduce wood waste while providing pallet users with quality, economical pallets. The study objectives were to evaluate the effect of MCP repair and reinforcement on pallet performance, and to evaluate preliminary standards for repair and reinforcement of pallets with MCPs. Whole pallets and pallet components were tested. Stringers and notched segments were tested in static bending, while end feet were tested for resistance to fork tine impact. Whole pallets were evaluated with a test protocol that simulated the effects of long-term handling. Stringers, repaired at notch corners, had greater strength, but less stiffness than the original stringers. Notch reinforcement with MCPs resulted in stringers with greater strength and stiffness than equivalent unreinforced stringers. No consistent species-width effect was found for strength of plated stringers. MCP-repair of above-notch failures did not restore the original strength or stiffness of notched segments. However, these repairs may be satisfactory since above-notch failures are secondary in frequency of occurrence. No differences were found between performance of plates used to repair stringers and notched segments. Both repaired and reinforced end feet had greater impact resistance than the equivalent original or unreinforced end feet. Wood species, rather than stringer width, had a greater influence on MCP performance. In general, tests of whole pallets supported the results from component tests which suggests that component testing may be a practical means of assessing the effect of repair and reinforcement techniques on pallet performance. / Master of Science

A large percentage of the total annual lumber production in the U.S.A is consumed by the pallet industry. However, standardized design procedures for these products have only recently been developed. A four-year cooperative pallet research, development and application program was undertaken by the National Wooden Pallet and Container Association, Virginia Polytechnic Institute and State University, and the U.S Forest Service. This research is directed towards developing standardized design procedures for both stringer and block-type pallets. Phase I dealt exclusively with stringer-type pallets while Phase II expands the scope to include block-type pallets. The objective of this work was to develop methods to analyze the effects of loads, supports and geometry on the response of block-style pallets. The developed analysis procedures are based on matrix structural analysis methods. A quarter symmetric 3-dimensional model is used to simulate pallets racked across the stringerboards (RAS) and a half symmetric 2-dimensional model is used for the racked across deckboards (RAD) and sling support modes. Both models are used in the stack condition. Deckboard/stringerboard joints are modeled as a single spring in the RAS model and the deck-block joint in both the RAS and RAD models are modeled as a framework of rigidly connected members and five springs (2 rotational and three axial). The procedure has the capability to handle both uniformly distributed and line loads in rack, stack, or sling support modes, and a wide variety of commonly used geometries. The developed analysis methodology is presented in computerized form and will provide the user a means of communication with pallet manufacturers for defining expected performance. / M.S.

Pallets are abundant throughout the supply chain with 2.6 billion pallets in circulation in the United States (Freedonia, 2015). More than 93% of goods are transported in the form of a palletized unit load (White and Hamner, 2005). Plastics are the second most commonly used material to manufacture these shipping platforms (Bond, 2018), yet there is a lack of information to be found about the plastic pallet industry's characteristics. Therefore, the main objective of this research was to investigate the status of the plastic pallet industry in the United States in 2018. To gather information, an online survey was conducted. It was sent out electronically to twenty-six plastic pallet manufacturers with response rate of 54%. The results have shown that almost 16 million plastic pallets were manufactured in the United States by the survey respondents in 2018. Of these, over 80% were multiple use pallets and about 80% were standard size. Most plastic pallets that were manufactured by the respondents were made with high pressure injection molding (63%) using high density polyethylene (HDPE) resin (68%). Close to 50% of the pallets had reinforcement beams and 12% had fiberglass reinforcement. Although most plastic pallets were manufactured using virgin resin, 34% were manufactured from recycled resin which reduces the cost and increases the sustainability of the plastic pallet. In addition, this study has shown that most of the plastic pallets manufactured in 2018 had no flame-retardant additives since only 20% from the respondents indicated that their pallets were Underwriter Laboratories (UL) or Factory Mutual (FM) certified. Based on these results, a new survey format and framework is designed with a recommendation to conduct it in every five years in order to further explore the state and market trends of the plastic pallet industry. / Master of Science / Pallets are abundant throughout the supply chain with 2.6 billion pallets in circulation in the United States (Freedonia, 2015). In 2005 it is estimated that more than 93% of goods are transported in the form of a palletized unit load (White and Hamner, 2005). Plastics are the second most commonly used material to manufacture these shipping platforms (Bond, 2018), yet there is a lack of information to be found about the plastic pallet industry's characteristics. Therefore, the main objective of this research was to investigate the status of the plastic pallet industry in the United States in 2018. To gather information, an online survey was conducted. It was sent out electronically to twenty-six plastic pallet manufacturers with response rate of 54%. The results have shown that almost 16 million plastic pallets were manufactured in the United States by respondents in 2018. Of these, over 80% were multiple use pallets and about 80% were standard size (48 in. x 40 in., 45 in. x48 in.). Most plastic pallets manufactured by the respondents were made with high pressure injection molding (63%) using high density polyethylene (HDPE) resin (68%). Close to 50% of the pallets had reinforcement beams and 12% had fiberglass reinforcement. Although most plastic pallets were manufactured using virgin resin, 34% were manufactured from recycled resin which reduces the cost and increases the sustainability of the plastic pallet. In addition, this study has shown that most of the plastic pallets manufactured in 2018 had no flame-retardant additives since only 20% from the respondents indicated that their pallets were Underwriter Laboratories (UL) or Factory Mutual (FM) certified. Based on these results, a new survey format and framework is designed with a recommendation to conduct it in every five years in order to further explore the state and market trends of the plastic pallet industry.

Pallets are the foundation of unit loads and supply chains. They provide a way to store and transport products in an efficient manner. The load capacity of pallets greatly depends on the type of packages carried by the pallet; however, current pallet design methods do not consider the effect of packages on the load carrying capacity of the pallet. This results in excessive use of materials which reduces the sustainability of unit loads, drives costs up, and creates issues for people in the supply chain. The objective of this study was to investigate the effect of a corrugated box's size and head space on pallet deflection and stress distribution on the top of the pallet as a function of pallet stiffness across multiple pallet support conditions. Data analysis identified that box size had a significant effect on the deflection of the pallet. This effect was only significant for warehouse racking across the width and length support conditions. As much as a 53% reduction in pallet deflection was observed for high stiffness pallets supporting corrugated boxes with 25.4 mm headspace when the size was increased from small to large. Meanwhile, no significant effect of box size was found for other supports. The effect of headspace was significant in some scenarios but inconsistent thus more investigation with a larger sample size is recommended. In addition, redistribution of vertical compression stresses towards the supports was observed as a function of the increasing box size. The increased concentration of compression stresses on top of the supports and the resulting lower pallet deflection could significantly increase the actual load carrying capacity of some pallet designs. / Master of Science / Pallets are the foundation of unit loads and supply chains. They provide a way to store and transport products in an efficient manner. The load capacity of pallets greatly depends on the type of packages carried by the pallet; however, current pallet design methods do not consider the effect of packages on the load carrying capacity of the pallet. This results in excessive use of materials which reduces the sustainability of unit loads, drives costs up, and creates issues for people in the supply chain. The objective of this study was to investigate the effect of a corrugated box’s size and head space on pallet deflection and stress distribution on the top of the pallet as a function of pallet stiffness across multiple pallet support conditions. The data from the study identified that box size does have an effect on the deflection of the pallet but, it was only found to be significant for the warehouse racking supports. The highest reduction in pallet deflection was 53% on the high stiffness pallets carrying corrugated boxes with 25.4 mm of headspace as the boxes increased in size. The other support conditions showed no significant effect of the box size. Headspace showed some significant effect in some conditions but was found inconsistent, therefore an investigation with a larger sample size is recommended. In addition, the redistribution of vertical compression stresses towards the supports was observed as a function of increasing box size. This increase in stress on the supports resulted in lower pallet deflection that could significantly increase the actual load carrying capacity of some pallet designs.