This paper studies the influence of displacement rate on mode II delamination of unidirectional carbon/epoxy composites. End-notched flexure test is performed at displacement rates of 1, 10, 100 and 500 mm/min. Experimental results reveal that the mode II fracture toughness GIIC increases with the displacement, with a maximum increment of 45% at 100 mm/min. In addition, scanning electron micrographs depict that fiber/matrix interface debonding is the major damage mechanism at 1 mm/min. At higher speeds, significant matrix-dominated shear cusps are observed contributing to higher GIIC. Besides, it is demonstrated that the proposed rate-dependent model is able to fit the experimental data from the current study and the open literature generally well. The mode II fracture toughness measured from the experiment or deduced from the proposed model can be used in the cohesive element model to predict failure. Good agreement is found between the experimental and numerical results, with a maximum difference of 10%. The numerical analyses indicate crack jump occurs suddenly after the peak load is attained, which leads to the unstable crack propagation seen in the experiment.
Stepladders are compact, foldable ladders with flat steps and a platform. Despite all the research and design efforts, there are still limitations in terms of the multifunctionality, usability and simplicity of stepladders and related variants. By combining ideas, features and functions from patent literature, existing products and scientific journals, this study aims to conceptualise a multifunctional stepladder for improved usability. Five concepts are created, which are screened and evaluated against a set of criteria to select the best concept for improved usability, divided into three categories: simplicity, effectiveness and efficiency. The result is a versatile invention that functions as a stepladder, walker, wheelchair and Pilates chair, suitable for older people and caregivers in nursing homes. It allows medical records or supplies to be retrieved from high places without the need for inappropriate aids. The invention can replace wheelchairs and walkers and converts into a Pilates chair to provide a mobile exercise option for older people. The concept offers older people flexibility and independence in terms of mobility and healthcare, while saving space in the nursing home. Further design studies, prototyping and testing are needed before this idea can go into production.