Hardened underground structures are purposely constructed beneath the ground surface for additional protection. The protection and sustainability of such a structure is provided by the soil overburden, supported by the structure's roof slab, also called a primary slab. The soil overburden usually contains one or more layers of protective reinforced concrete slabs, defined as secondary slabs. Hardened sub-surface structures can experience a degree of damage from sub-surface explosions, caused by the detonation of airborne weapons at variable depths within the soil overburden layer. The research objective was to evaluate the degree to which material and geometric parameters influenced the magnitude of groundshock loading and hence the severity of damage to sub-surface positioned reinforced concrete slabs. The work was of an experimental nature, performed within a purposely built test cell. The experimental set-up involved positioning cylindrical charges within the soil overburden at variable standoffs from an initially positioned steel plate, then from a primary slab, which was subjected to a series of cumulative loadings. The structural response of both the steel plate and a reinforced concrete slab were evaluated using an energy balance procedure. A parametric study was performed, determining the influence each geometric parameter had to the magnitude of groundshock loading. The variability of data associated with the material parameters was analysed and compared to the published literature. Numerical simulations were performed at the end of the experimental stage (using the non-linear finite element programme AUTODYN21)) to investigate phenomena that could not be investigated experimentally. A visual damage assessment in the form of a crack pattern analysis and chronological order of occurring mechanisms upon reinforced concrete slabs was performed. The severity of damage to the primary slabs was then associated with the cumulative load impulse history. The research yielded the following conclusions: I. An idealised half sine-wave load distribution approximated the pressure-time history profiles recorded by pressure gauges. 2. The steel plate and one concrete slab (for which conclusive data was obtained) responded impulsively to groundshock loading. 3. The magnitude of groundshock loading was most sensitive to a change in the charge standoff. 4. The reduction in the soil overburden above the top face of a secondary slab did not influence the groundshock loading induced into a primary slab. 5. The effect of the propagating groundshock wave overrode any initial form of soil compaction between the charge and target. This was due to the significantly high stresses induced into the soil, which were well above the initial insitu stresses. 6. Internal weakening of a primary slab, which was unidentifiable from the external damage, caused significant loss in structural strength and stiffness.

This thesis comprehensively investigates the contour method - a newly-invented destructive technique for residual stress evaluation - in terms of its principle and application. The principle of the contour method is based on a variation of Bueckner's elastic superposition theory. A two-dimensional map of residual stress profile normal to a plane of interest can be determined in a simple, cheap and time-efficient manner. In practice,residual stress evaluation using the contour method involves the experimental measurement of the displacement formed by the stress release following a cut on the surface at issue, and then numerical calculation of the residual stress based on the experimentally measured displacement. The whole process of the contour-method measurement was simulated using a finite element method and the simulated result confirms the correctness of the novel technique. A number of different applications have been explored using the contour method to measure a cross-sectional residual stress distribution: a hole cold expansion EN8 steelplate, a hole cold expansion 7475-T7351 aluminium alloy plate, a MIG 2024-T351 aluminium alloy welded plate and a VPPA 2024-T351 aluminium alloy welded plate. Favourably good outcomes were obtained from each case. The most impressive comparison of the contour-method result was made on the VPPA 2024-T351 weld with neutron and synchrotron X-ray diffraction measurements, showing an extremely good match with deviation approximately 9 % on average. This work has proved that the contour method is a powerful novel technique to determine across-sectional residual stress profile with accuracy in many engineering components, and has great prospects to find application elsewhere.

No description available.

This thesis is concerned with the interfacial and durability aspects of Extrinsic Fabry-Perot Interferometric (EFPI) sensors embedded in carbon fibre reinforced composites. Fibre optic sensors are being used in many long term applications and, as is the case for all sensor types, the ability of the EFPI sensors to monitor accurately the measurands of interest over the lifetime of the structure must be proved. Therefore, the aim of this work was to examine the interface between the EFPI sensors and the structures, and then to evaluate the durability of that interface and the sensors. The first stage was an examination of the EFPI sensors including the method of manufacture, interrogation option and inherent strength of the sensors. It was found that the sensors have a very low tensile load to failure (~0.5 N). This was improved by using a resin reinforcement, which was applied to the capillary ends. However, this had implications for the overall sensor size and that influenced their embedment suitability. The second stage was interfacial characterisation; this was achieved through the examination of the surface energy of the sensors, carried out by contact angle measurements; and the interfacial shear strength of the sensors to matrix, using a new variation on the single fibre pull-out technique that involved the use of optical fibres and composite prepreg. Overall, it was found that the silane treatment of the fibres increased the surface energy but for the interfacial shear results the data was less conclusive due to the scatter present within the results. The durability of the sensors was examined through their embedment into carbon fibre composite samples and exposure to tension/compression fatigue loading. From initial quasi-static work it was found that the embedment of the sensors had no significant effect on the composite samples. However, the sensors failed at a strain levels of 0.4% in tension and at 1.1% in compression; the compression strain level was at the point of composite failure. Under fatigue loading the sensors could survive a million cycles at R=-1 at a max stress level of 156 MPa and maintain their reliability. If the tensile loading was increased then the sensors would fail within a few thousand cycles. However, if the compressive stress was increased the sensors survived but the reliability was affected. Overall, it was felt that with some improvements to the sensor design they should be able to survive and provided useful data when exposed to axial tension/compression fatigue regimes.

Instrumented indentation techniques at micro or nano-scales have become more popular for determining mechanical properties from small samples of material. These techniques can be used not only to obtain and to interpret the hardness of the material but also to provide information about the near surface mechanical properties and deformation behaviour of bulk solids and/or coating films. In particular, various approaches have been proposed to evaluate the elastic-plastic properties of power-law materials from the experimental loading-unloading curves. In order to obtain a unique set of elastic-plastic properties, many researchers have proposed to use more than one set of loading-unloading curves obtained from different indenter geometries. A combined Finite Element (FE) analysis and optimisation approach has been developed, using three types of indenters (namely, conical, Berkovich and Vickers), for determining the elastic-plastic material properties, using one set of ‘simulated’ target FE loading-unloading curves and one set of real-life experimental loading-unloading curves. The results obtained have demonstrated that excellent convergence can be achieved with the ‘simulated’ target FE loading-unloading curve, but less accurate results have been obtained with the real-life experimental loading-unloading curve. This combined technique has been extended to determine the elastic and visco-plastic material properties using only a single indentation ‘simulated’ loading-unloading curve based on a two-layer viscoplasticity model. A combined dimensional analysis and optimisation approach has also been developed and used to determine the elastic-plastic material properties from loading-unloading curves with single and dual indenters. The dimensional functions have been established based on a parametric study using FE analyses and the loading and linearised unloading portions of the indentation curves. It has been demonstrated that the elastic-plastic material properties cannot be uniquely determined by the test curves of a single indenter, but the unique or more accurate results can be obtained using the test curves from dual indenters. Since the characteristic loading-unloading responses of indenters can be approximated by the results of dimensional analysis, a simplified approach has been used to obtain the elastic-plastic mechanical properties from loading-unloading curves, using a similar optimisation procedure. It is assumed that the loading-unloading portions of the curves are empirically related to some of the material properties, which avoids the need for time consuming FE analysis in evaluating the load-deformation relationship in the optimisation process. This approach shows that issues of uniqueness may arise when using a single indenter and more accurate estimation of material properties with dual indenters can be obtained by reducing the bounds of the mechanical parameters. This thesis highlights the effects of using various indenter geometries with different face angles and tilted angles, which have not been covered previously. The elastic-plastic material parameters are estimated, for the first time, in a non-linear optimisation approach, fully integrated with FE analysis, using results from a single indentation curve. Furthermore, a linear and a power-law fitting scheme to obtain elastic-plastic material properties from loading-unloading indentation curves have been introduced based on dimensional analysis, since there are no mathematical formulas or functions that fit the unloading curve well. The optimisation techniques have been extended to cover time-dependent material properties based on a two-layer viscoplasticity model, has not been investigated before.

The strain gauge is a physical sensor, in which the influence of an externally applied strain causes the resistance to undergo a reversible change. It can be applied to the measurement of force, pressure, and displacement etc. The thick film strain gauge is relatively new however and has been seen to have many advantages. System zero (offset) and system gain (sensitivity) are key characteristics of the strain gauges. Hence intensive research was carried out to study these two aspects of different construction types of thick film strain gauges, i.e. X-plane and Z-plane strain gauges. Different fabrication parameters of these devices were studied for their effect on the characteristic. Temperature characteristics of both of these types of devices were examined as a measure of system zero stability. Combinations of resistor thickness, construction materials and geometric parameters of these types of devices were noticed to affect their temperature behavior. These observations would undoubtedly facilitate the achievement of good TCR matching between resistors in practical application. A programme of explanatory theory to understand these observations has been submitted, which comprises strain analysis and conduction mechanism study. Loading characteristics of Z-plane strain gauges have also been studied to explore the potential of this type of device.