• Preetish Ramasawmy

    Student thesis: Doctor of Engineering


    Steel racks are complex freestanding structures that are used to store goods on pallets. The complexity of their structural response to impact loads poses many challenges. In the prevailing competitive market, steel racks must be light yet still be able to withstand high impact loads. Ultimately, they should be manufactured as economically as possible. Two types of rack structures are predominant in most warehouses; selective and drive-in. Existing racking standards, such as the BS EN 15512:2009, and rack design guidelines, such as FEM 10.2.02 discuss the design limitations of racking legs but only minimally address the issue of impact behaviour. Selective rack is a pallet rack in which every pallet is stored on a horizontal beam and is accessible from an aisle. Drive-in racks however are normally three to nine pallets deep and require minimal floor space; achieved by storing pallets on rail beams, one after the other, with nominal space between them. The forklift truck drives into the rack to position the pallets on the first-in, last-out code. To allow passage, drive-in racks are normally braced at the back and at the top in the down-aisle direction resulting in a complicated structure with poorly understood mechanical behaviour and increased risk of impact. When subjected to an impact force, the bowing of a racking leg may trigger progressive failure of a whole racking structure. Data that adequately describes the 3D behaviour and mechanism of racking legs during a range of impact conditions is not currently available. This thesis provides pertinent data thereby bridging the gap in the understanding of the behaviour of racking legs. It is further motivated by the need to minimise catastrophic collisions from impact loads experienced by racking legs; achieved through the creation of a novel rackguard with superior energy absorption capabilities. The research will assess the energy absorption capability of an A-Safe Ltd rackguard made from a new blend of materials - high-density polyethylene, thermoplastic elastomer and glass fibre (HDPE/TPE/GF). Current guidelines state that racking legs must be able to withstand impact energy of up to 400 joules with a maximum permanent deflection of 3mm. The material will be subjected to impact energy of 400 Joules and its response evaluated. Experimental results are presented for tensile, compression, shear and three-point bending experiments performed on 80% HDPE/ 10% TPE/ 10% GF samples. Improvements in testing methodologies are made to increase experimental and numerical modelling accuracy. Experimental results from tensile tests conducted on ASTM D638 Type 4 specimens are presented where the effects of gauge length and strain-rate sensitivity are investigated. The mechanisms involved in double yielding of HDPE/TPE/GF in compression is also presented through experimental testing. Shear test results show the influence of notch depth and notch angle on strain localisation and uniformity between the notches. Using 3D DIC optical method, accurate and representative material behaviour is obtained in the form of true stress-true plastic strain. From the results, recommendations are proposed in detail, for an improved shear specimen design, and hence a robust test procedure to generate reliable material strain data. Finite Element Analysis (FEA) results show that the rackguard significantly minimises the impact energy transferred to the rack leg and influences the overall displacement to less than 3 mm for all scenarios with the exception of a point load side impact. Furthermore, using FEA, the influence of impactor geometry and impact height on the rackguard and rack legs behaviour are analysed and reported herein. The rack leg is modelled using Johnson-Cook material model while the rackguard is modelled using SAMP-1 material model. FEA requires accurate material model, calibrated from reliable experimental data to describe material behaviour. SAMP-1 is used to model the rackguard because of
    Date of Award31 Dec 2017
    Original languageEnglish
    Awarding Institution
    • The University of Manchester
    SupervisorZhenmin Zou (Supervisor) & Qing Li (Supervisor)


    • Drop Weight Test
    • Double Yield Point
    • Injection Moulding
    • Notch Depth/Notch Angle
    • SAMP-1
    • Strain rate sensitivity
    • Polymers

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