G.S. Langdon

Learning as acquiring a discursive identity through participation in a community: improving student learning in engineering education

In this paper, we propose that learning in engineering involves taking on the discourse of an engineering community, which is intimately bound up with the identity of being a member of that community. This leads to the notion of discursive identity, which emphasises that students’ identities are constituted through engaging in discourse. This view of learning implies that success in engineering studies needs to be defined with particular reference to the sorts of identities that students develop and how these relate to identities in the world of work. In order to achieve successful learning in engineering, we need to recognise the multiple identities held by our students, provide an authentic range of engineering-related activities through which students can develop engineering identities and make more explicit key aspects of the discourse of engineering of which lecturers are tacitly aware. We include three vignettes to illustrate how some of the authors of this paper (from across three different institutions) have applied this perspective of learning in their teaching practice.

The Blast Behavior of Fiber Reinforced Thermoplastic Laminates

This article presents the results of a series of blast tests on a carbon fiber-reinforced poly-ether-imide (PEI) and a glass fiber-reinforced PEI composite. Initially, the fracture properties of the two composite systems were characterized through a series of flexural and interlaminar fracture tests. Blast testing was then undertaken on a ballistic pendulum facility, capable of measuring the impulse imparted by the plastic explosive. Delamination, localized fiber buckling, fiber fracture, and shear failure at the boundary of the clamped plates were identified as the primary failure mechanisms in the laminates, with their severity depending on the panel thickness and the applied impulse. Delamination was very localized along the center plane of the laminate, a reflection of the very high interlaminar fracture toughness of these composites. The critical impulse for rear surface fiber fracture has been found to increase rapidly with laminate thickness for the range of panels considered here. The impulses associated with the onset of rear-surface fiber fracture and complete failure of the target were similar, suggesting that rear surface fiber fracture is a pre-cursor to complete failure in these laminates. Limited tests on the glass fiber-reinforced PEI system showed that it offers a superior blast resistance to its carbon fiber counterpart.

The response of polymeric composite structures to air-blast loading: a state-of-the-art

Abstract Composite materials are finding use in an increasing number of structural applications as a result of their high specific strength, high specific stiffness, thermal resistance and the potential for tailoring of properties to suit specific applications. Fibre-reinforced composites, foam core sandwich panels and fibre-metal laminates (FMLs) are examples of composite materials that are employed in high-performance engineering applications, for example in yachts, passenger aircraft, racing cars and sports equipment. Explosive loading is a potential threat to many of these structures, and therefore an improved understanding of the response of such systems to air-blast loading is important. This paper reviews recent experimental and numerical work on the response of composite materials, sandwich structures and hybrid materials to air-blast loading. Commonly employed experimental techniques used to simulate air-blast loading conditions are described, along with the results from recent experiments on plain composite laminates, polymeric sandwich panels and FMLs. The influence of loading distribution, materials and test geometry on the failure of composites is discussed. The latter part of paper discusses numerical modelling considerations and reports methods and results from recent numerical modelling work on the blast loading of composites.

The quasi-static and blast response of steel lattice structures

Lattice structures based on two simple architectures have been manufactured from 316L stainless steel using the selective laser melting process. The compressive properties of structures based on a body-centered cubic (BCC) and a similar structure with vertical pillars (BCC-Z) were initially investigated at quasi-static rates of strain. Blast tests were subsequently performed on the lattice structures as well as on lattice sandwich structures with CFRP skins. When subjected to quasi-static compression loading, the BCC structure exhibited a progressive mode of failure, whereas the BCC-Z lattice deformed in a buckling-dominated mode of collapse. The blast response of the lattice cubes exhibited a linear dependency on the applied impulse up to the threshold for material densification. Relationships between the blast resistance and both the yield stress and energy absorption characteristics of the lattices have been established and an examination of the failed samples indicated that the collapse modes were similar in both the quasi-static and blast-loaded samples. Finally, the failure modes observed in the blast-loaded sandwich panels were investigated and found to be similar to those observed in the lattice blocks.

Understanding the behaviour of fibre metal laminates subjected to localised blast loading

The modelling particulars of the response of Fibre-Metal Laminates (FML) to localised blast loading are discussed, particularly considering the debonding failure at the composite-metal interface. Attention is paid to the though-thickness transient deformation process in order to interpret the deformation mechanism due to highly localised pressure pulses. The study is based on previously reported experimental results on FML panels comprising different numbers of aluminium alloy layers and different thickness blocks of GFPP material. Good agreement between the experimental results and numerical predictions is demonstrated. A brief comparison between the response of a relatively thin FML panel and a monolithic aluminium alloy plate is presented.

The Response of Honeycomb Core Sandwich Panels, with Aluminum and Composite Face Sheets, to Blast Loading

The results of blast tests on sandwich panels with honeycomb cores are reported. Two core heights (13 mm and 25 mm) and two face sheet materials (glass fiber epoxy composite and aluminum alloy) were investigated. Increasing the core thickness reduced the permanent displacements exhibited by the sandwich panels. The panels with composite face sheets also exhibited smaller residual displacements than the aluminum face sheet counterparts. Damage took the form of core crushing, core shearing, debonding of the face sheet from the core, permanent displacement, cracking of the composite face sheets, and tearing. Higher damage levels were observed at elevated impulse levels. Load localization was found to concentrate the damage to the central portion of the panel, preventing the whole panel being employed in resisting the blast.

The blast resistance of a woven carbon fiber-reinforced epoxy composite

The blast resistance of a carbon fiber-reinforced epoxy (CFRE) resin has been investigated through experiments on a range of panels. The panels were subjected to blast loading by detonating small quantities of plastic explosive at a fixed stand-off distance. A ballistic pendulum was used to provide a measure of the impulse imparted to the specimen. Tests were undertaken at impulses up to those required to completely destroy the laminates. An examination of the damaged panels highlighted a number of different fracture mechanisms including delamination, top surface fiber buckling, fiber fracture, and shear failure along the edges of the plates. The impulses associated with the onset of fiber fracture and complete target failure were found to increase in a linear fashion for the range of panels considered here. The experimental data are compared with previously published results from similar tests on a woven carbon fiber-reinforced poly-ether-imide. Here, it was demonstrated that the CFRE offered a similar blast resistance to that of the thermoplastic—matrix composite.

Sandwich Panels Subjected to Blast Loading

The ability of sandwich panels to resist dynamic loading has been shown to be superior to monolithic metal plates of the same areal density by a number of investigators. Experimental and numerical studies on the response of sandwich panels to air-blast, water-blast and “simulated blast” are increasing, but mainly focus on the latter two. Three types of sandwich panels are identified, by core type: cellular core, micro-architectural core (small-scale lattice type) and macro-architectural core (larger scale plastic deforming elements). With advances in manufacturing techniques, several new core topologies have emerged which can allow core properties to be tailored according to design requirements (of which blast resistance may only be one factor), for example, lattice cores formed by selective laser-melting and metallic fiber cores. This chapter provides an overview on the state-of-the-art in the field of sandwich panel protection under blast and dynamic loading.

Fiber–Metal Laminate Panels Subjected to Blast Loading

Fiber–metal laminates (FML) are hybrid metal and composite structural materials that have been attracting interest due to the improved fatigue and impact resistance reported in the literature (J Mater Proc Tech 103:1–15, 2000; Int J Impact Eng 18(3):291–307, 1996; Compos Struct 61:73–88, 2003; Appl Comput Mater 11:295–315, 2004). Much less is known about their performance under blast loading conditions, as until recently there was very little written in the literature on this subject. This chapter reviews experimental and numerical studies that focus on the blast response of FMLs manufactured from aluminium alloy and glass fiber-reinforced polymer layers. Herein, the difference in response to localized and uniformly distributed blast loading are reviewed, application of nondimensional analysis techniques used for steel are described, and any potential advantages of FMLs over the equivalent areal density metal panels are highlighted.

The blast response of composite and fibre-metal laminate materials used in aerospace applications

The blast behaviour of composite materials is a subject of growing importance generally due to the ever-present threat of subversive activity. The aircraft industry will employ composite materials more frequently in the future as they are lightweight, offer superior fatigue resistance, life cycle cost savings, fuel efficiency and (in some cases) improved impact properties, when compared with monolithic metals such as aluminium alloy. However, little is known about their response to blast loading. This chapter provides a brief introduction to the characteristics of explosions and demonstrates that a careful assessment of the blast loading scenarios for each aircraft design is required, as the loading is complicated by the degree of confinement, geometric variations and the multiplicity of potential explosion scenarios. Various blast protection paradigms are reported, with the containment strategy being most relevant for aircraft design at present. Recent experimental and numerical investigations concerning the blast behaviour of aerospace composites are reported. The response of fibre-reinforced polymers, polymeric sandwich panels and multilayered fibre-metal laminate (FML) structures are discussed in the context of the aerospace environment.