A finite element study of fatigue crack propagation in single lap bonded joint with process-induced disbond

This paper presents a method for predicting fatigue crack propagation in adhesive bonded composite joints with an initial full-width disbond using finite element analysis and numerical integration of the material's fatigue crack growth rate law. Fatigue tests were conducted on single lap joints. Crack lengths were monitored from four runout corners. In-situ crack growth measurements were performed by ink injection to identify the crack front profile during fatigue loading. The crack growth was modelled using a fracture mechanics criterion considering two different crack propagation patterns. The material's fatigue crack growth rate law was determined experimentally using the standard double cantilever beam and end notch flexure specimens. Using the total strain energy release rate and the two crack scenarios, the numerical model predicted the lower and upper bounds of the measured fatigue crack growth rates of the lap joint

Experimental and numerical study of process-induced defects and their effect on fatigue debonding in composite joints

Laboratory coupon joints for fatigue debonding tests usually have narrow width and a through-width initial disbond. However, realistic structural joints are much wider and may contain process-induced defects and accidental damage; both are much smaller than the joint width. Small and discrete damage may behave differently from the idealised through-width disbond crack. This has brought a question on whether the laboratory coupon joint can accurately represent the fatigue behaviour of wider structural joints. This paper presents an experimental and numerical study of fatigue behaviour of a wide bonded lap joint with a process-induced defect of semi-circular shape. Fatigue debonding propagation was monitored by ultrasound inspection. Fatigue life was predicted using a normalised strain energy release rate parameter calculated by finite element method, and the adhesive material fatigue crack growth rate data measured under single and mixed mode conditions. Simulation of process-induced defect and validation by experiments have brought a better understanding of fatigue debonding behaviour in wide joints containing realistic damage. Suggestions are given for fatigue fracture tests of bonded joints

Gated communities: Definitions, causes and consequences

Gated communities became an 'object of study' in the 1990s as social scientists observed their growth in several cities; they are now a feature of the urban landscape in most cities around the world. The expansion of gated communities has led to prolific research, examining different aspects of this type of residential development and providing evidence from case studies worldwide. This paper reviews how gated communities are conceptualised according to the literature and identifies the main factors influencing their development. It also considers spatial, economic, political and social consequences of the development of gated communities. These elements should be taken into account by planners and policymakers to minimise their negative impacts and maximise the positive consequences of a residential option that is likely to be part of the urban landscape for a long time

Organising Somalian, Congolese and Rwandan migrants in a time of xenophobia in South Africa: empirical and methodological reflections

Xenophobic practices pervade civil society and the state in South Africa. But its victims are not passive. Academic scholarship has not sufficiently recognised the multiple roles of refugees and asylum seekers migrant organisations in a context where refugees are required to "self-settle”. The dominant methodological focus of existing research has been on the migrant as the individual. This paper’s main research objectives are to question this focus and examine evidence of the collective responses to struggles faced by foreign African migrants and refugee groups in Cape Town. Eleven refugee and asylum seeker associations formed by Somalians, Congolese and Rwandan asylum seekers and refugees were investigated, based on extensive interviews with 11 leaders of refugee organisations. These organisations not only strongly defend migrant interests but also project a long-term view of integration into South African society. In addition, the paper concludes by arguing for a shift in the focus of research in order to show that migrant organisations are crucial in an individual’s collective security concerns, in advocacy with government institutions and in initiatives to build relationships with South Africans