Masonry arch bridges with observed or suspected defects require effective structural health monitoring to ensure their safety under increasing traffic loads. Traditional methods, such as visual inspections, provide only qualitative assessments and do not capture the variations in key local and global response characteristics under traffic loading. More advanced structural health monitoring techniques can measure the variations in displacements and strain fields under traffic; however, they typically require contact sensors and partial or complete occupation of the monitored spans. This study examines, for the first time, the application of 3D Digital Image Correlation (DIC) as a non-invasive method for monitoring masonry arch bridges in the field. It offers a refined 3D DIC monitoring technique specifically designed for such structures under traffic loading, providing improved accuracy through various error mitigation strategies. Using a case study of the Mill Road Viaduct, a multi-span railway bridge in Lewisham (London, UK), 3D DIC effectively captured full-field displacements and crack openings caused by live traffic loads. The results revealed significant 3D effects, particularly in the arch barrel, and confirmed crack development in different directions, highlighting the superiority of 3D DIC monitoring over the conventional 2D DIC counterpart. The accuracy of the 3D DIC measurements was validated against 3D scanning data, demonstrating its reliability for bridge monitoring applications. Despite its advantages, factors such as camera stability, environmental noise and calibration complexities are identified in this paper as critical challenges that should be addressed for successful deployment in the field. This study highlights 3D DIC as a realtime, high-resolution structural monitoring tool, offering valuable insights for proactive maintenance strategies.

3D laser scanning and digital image correlation (DIC), two novel techniques capable of non-contact, full-field measurements of surface geometry and deformations respectively, have emerged and gained increasing applications in structural engineering research. The aim of the present study is to provide a state-of-the-art review and best-practice guidance on 3D laser scanning and DIC in the context of structural testing, and to introduce their main applications and advantages in physical experiments on metallic structures. For 3D laser scanning, the basic principles and general applications are firstly introduced. Laser scanning of a generic structural steel sample is subsequently described as a case study to demonstrate the workflow, with recommendations provided on the best practice. 3D laser scanning has been utilised in structural experiments for determining dimensional parameters, examining surface topography, characterising geometric imperfections of different forms and representing true geometry in finite element modelling, examples of which, along with corresponding data analysis methods, are provided and discussed. For DIC, following an initial review, the procedure for setting up a stereo DIC system in a stub column test is subsequently presented, where recommendations are provided on the setup, speckle pattern, execution and data processing. Example applications of DIC in various types of structural experiments, ranging from material tests to geometric imperfection measurements, structural element tests and structural system tests, are subsequently presented, and the advantages offered by DIC over conventional measurement methods are discussed. 3D laser scanning and DIC provide structural researchers with deeper insights into the geometric properties and behaviour of metallic structures in physical experiments, and the presented work will help to facilitate the broader and more effective use of these techniques among peer researchers.

The primary aim of the present study is to explore the use, advantages and potential of two advanced data acquisition techniques – 3D scanning and digital image correlation (DIC), in the testing of metallic structures. 3D scanning is a novel method for capturing the full outer geometry of an object. It is being increasingly used in experimental studies for the determination of dimensional parameters and the characterisation of local and global imperfections, examples of which are given and discussed. Digital image correlation (DIC) is a rapidly evolving technology for the full‐field measurement of the displacements and strains over a surface. A brief introduction to DIC and its workflow is firstly provided. Example applications of DIC in various scales of experiments, including material tests, structural element tests and full‐scale structural system tests, are subsequently discussed. These new‐generation data acquisition techniques enable structural researchers to gain a deeper insight into the behaviour of metallic structures in experimental research.

The recent advances in the additive manufacturing (AM) have enhanced the development of light-weight, energy-absorbing structures in many aspects with precise, designed configurations of the internal structure. Given the range of potential materials many possible variations exist compared to the existing polymer-based foams. The advantages of rapid prototyping, enabled through AM, allows a streamlined process in obtaining a structure of desired mechanical behaviour. In this work, development, and design variation of a flexible lattice structure with core strut modification is demonstrated. The core struts are varied in terms of shape and density and are fabricated using vat photopolymerisation with Formlabs Flexible 80A resin and experimental methodology is outlined for the characterisation of the printed specimen under compressive loading. Mechanical characterisation under three different compression rates presents that the implementation of the core strut increases the elastic modulus of the lattice structure. The enhanced stiffness effects are further increased with the variations in shape, while the evaluation of the density variations shows significantly different deformation behaviour and strain rate sensitivity. The behaviour of each specimen types is discussed further in terms of their functional viability and potential applications where the design specific behaviour and small, lightweight form factor can be most effectively utilised.

This chapter describes the various methods by which the changing positions of large numbers of stations can be monitored by standard surveying methods. Once the network of fixed stations has been measured, the detection of displacements due to ground deformation will depend upon a later re-measurement of the same stations. The best site for a tilt station or tiltmeter under this kind of deformation regime would therefore be near the point of maximum inclination on the flanks, whereas a network measuring horizontal deformation would be best placed across the summit. Despite the maximum vertical deformation at the summit, tilt is zero here, and reaches maximum values on the flanks. The best way to achieve this information rapidly is with a trilateration network that also includes trigonometric levelling. For levelling traverses on active volcanoes, a self-levelling instrument is virtually essential because of the necessity for speed, and will correct small changes in horizontality of the instrument.

Metal foams are often used as energy absorbers and lightweight materials. Inspired by a natural blueprint, open‐cell metal foams can significantly reduce the mass of a structure. The innovative manufacturing process of electrodeposition provides the possibility to customize the coating layer thickness of nickel (Ni) on a polyurethane (PU) precursor foam. Consequently, the mechanical properties can be adjusted according to the requirements of the expected application. Herein, quasistatic compression tests and low‐velocity impact tests are conducted on open‐cell Ni/PU hybrid foams to investigate the strain‐rate effects for strain rates in the range of 10−3 to 550 s−1. Furthermore, digital image correlation is performed with the intention of comparing the micromechanical deformation mechanisms under quasistatic loading with those under dynamic loading. For the first time, the heat evolution at different impact velocities of metal foams has been investigated with an infrared camera.

Characterising material properties of ligaments is essential in the analysis of human morbidity and mortality of low-speed sporting accidents, high-speed road traffic accidents, and very high-speed battlefield injuries. At lower strain rates the elastic modulus and ultimate stress increase relative to strain rate, although very high strain rate testing has not been performed to date.A porcine stifle joint lateral collateral ligament experiment was conducted that simulated the strain rates that occur during across a full range of different human knee ligament injuries. Tensile testing was performed at five strain rates, each an order of magnitude apart, in the range 100–104%/s. Seven specimens were tested at each rate. Three loading techniques were used: 1) screw-driven, 2) servo-hydraulic, 3) drop weight rig with tensile impact adaptor. Cross sectional area was measured by counting pixels on a standardized digital photograph of an alginate-paste cast of the mid-substance of each sample. Strain was measure...

AbstractOpen‐cell metal foams are a new class of cellular materials with structural features resembling those of lightweight load‐bearing materials such as cancellous bones and wood. Their high stiffness‐to‐weight ratio coupled with their typical long, flat stress‐strain response make them ideal candidates as cost‐effective shock energy absorbers in crashworthiness, impact loading and blast mitigation strategies. The macroscopic mechanical properties of foams are strongly influenced by both the mechanical behaviour of single pores at the mesoscopic level and the struts and their structure at the microscopic length‐scale, based on a strong structure‐property relationship. This is shown in the present contribution where an experimental‐numerical investigation has been conducted demonstrating the existence of strain‐rate effects at different hierarchical scales. Micro inertia effects arising due to the pore geometry as well as further strain‐rate effects stemming from the rate‐sensitivity of the Ni coating in Ni/Al hybrid foams are also outlined. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

New engineered materials have critical applications in different fields in medicine, engineering and technology but their enhanced mechanical performances are significantly affected by the microstructural design and the sintering process used in their manufacture. This work introduces (i) a methodology for the calculation of the full deflection profile from video recordings of bending tests, (ii) an optimisation algorithm for the characterisation of Young's modulus, (iii) a quantification of the effects of optical distortions and (iv) a comparison with other standard tests. The results presented in this paper show the capabilities of this procedure to evaluate the Young's modulus of highly stiff materials with greater accuracy than previously possible with bending tests, by employing all the available information from the video recording of the tests. This methodology extends to this class of materials the possibility to evaluate both the elastic modulus and the tensile strength with a single mechanical test, without the need for other experimental tools.

We describe the capability of a high-resolution three-dimensional digital image correlation (DIC) system specifically designed for high strain-rate experiments. Utilising open-source camera calibration and two-dimensional DIC tools within the MATLAB framework, a single camera three-dimensional DIC system with submicron displacement resolution is demonstrated. The system has a displacement accuracy of up to 200 times the optical spatial resolution, matching that achievable with commercial systems. The surface strain calculations are benchmarked against commercially available software before being deployed on quasi-static tests showcasing the ability to detect both in- and out-of-plane motion. Finally, a high strain-rate (1.2x10(3)s(-1)) test was performed on a top-hat sample compressed in a split-Hopkinson pressure bar in order to highlight the inherent camera synchronisation and ability to resolve the adiabatic shear band phenomenon.

There is considerable interest in the high-rate compaction of brittle granular materials such as sand. However, the vast majority of studies focus on a single granular system, limiting our ability to make comparisons between materials to discern how granular structure manifests as bulk material response. Here, three different silica sands with similar grain size and shape are studied: we compare a rough quarry sand, a smoother-grained sand, and a sandy loam. Quasi-static compaction and planar shock loading responses are compared, and recovered samples analyzed. The combination provides information regarding the interplay between granular properties, loading conditions, and material response. We show that the fundamental grain-scale behaviour depends on loading conditions: At low strain rates compaction behaviour is dominated by grain morphology, and in particular, smoothness and particle size distribution. Under shock loading, grain rearrangement and force chain effects are suppressed, and the nature of inter-granular contact points, modified by the presence of moisture or fines, is most important. Furthermore, grain fracture under shock loading is substantially reduced with increasing moisture content.

Metal foams are used as absorbers for kinetic energy but predominantly, they have only been investigated under quasi-static load-conditions. Coating of open-cell metal foams improves the mechanical properties by forming of Ni/Al hybrid foam composites. The properties are governed by the microstructure, the strut material and geometry. In this study, the strain-rate effects in open-cell aluminium foams and new Ni/Al composite foams are investigated by quasi-static compression tests and low-velocity impact. For the first time, drop weight tests are reported on open-cell metal foams, especially Ni/Al composite foams. Furthermore, size-effects were evaluated. The microstructural deformation mechanism was analysed using a high-speed camera and digital image correlation. Whereas pure aluminium foams are only strain-rate sensitive in the plastic collapse stress, Ni/Al foams show a general strain-rate sensitivity based on microinertia effects and the rate-sensitive nano-nickel coating. Ni/Al foams are superior to aluminium foams and to artificial aluminium foams with equal density.

Predictive computational modeling of the response of armor systems to dynamic threats such as blast and impact requires understanding and quantification of the behavior of the armor materials. This paper describes the mechanical characterization of Dyneema HB26. The in-plane tensile, compressive, and shear stress-strain behavior and strength of the laminate at low rates has been determined experimentally. The tensile behavior of the Dyneema SK76 fibers, which comprise 83% of the laminate has been determined, including the effect of temperature and rate. (C) 2014 American Society of Civil Engineers.

Alumina (aluminum oxide, Al2O3) particles are pelletised and fired to produce high porosity catalyst pellets of complex shapes. These pellets fill cylindrical reactor columns with particulate packing structures that are key to the in-service performance, but will suffer breakages which impact on catalyst performance. The combined FiniteDiscrete Element Method (FEMDEM) is ideally suited to the simulation of both the multi-body pellet dynamic packing and quasi-static interactions as well as the stress field of each individual pellet, its deformations and fragmentation. The application of FEMDEM fracture modelling to a fine-grained brittle and porous material is novel. This paper presents a methodology for a validation study through comparison with three pointbending and Brazilian tests and discusses FEMDEM's potential in modelling multi-body fragile systems.

The material properties of ligaments are not well characterized at rates of deformation that occur during high-speed injuries. The aim of this study was to measure the material properties of lateral collateral ligament of the porcine stifle joint in a uniaxial tension model through strain rates in the range from 0.01 to 100/s. Failure strain, tensile modulus and failure stress were calculated. Across the range of strain rates, tensile modulus increased from 288 to 905 MPa and failure stress increased from 39.9 to 77.3 MPa. The strain-rate sensitivity of the material properties decreased as deformation rates increased, and reached a limit at approximately 1/s, beyond which there was no further significant change. In addition, time resolved microfocus small angle X-ray scattering was used to measure the effective fibril modulus (stress/fibril strain) and fibril to tissue strain ratio. The nanoscale data suggest that the contribution of the collagen fibrils towards the observed tissue-level deformation of ligaments diminishes as the loading rate increases. These findings help to predict the patterns of limb injuries that occur at different speeds and improve computational models used to assess and develop mitigation technology.

A simple experimental method for determining a set of triaxial properties for concrete and other geologically based materials such as rock and soil is described. The method involves the uniaxial loading of a cylindrical material specimen that is radially confined by a steel tube. The steel tube is lined to reduce friction and is externally strain gauged to determine axial and circumferential strains. Elastic thick-cylinder theory is then applied to determine the radial stresses and strains induced in the specimen during uniaxial loading. The specimen load conditions are approximately those of uniaxial strain, with lateral strains being two orders of magnitude lower than the axial strains. The test is capable of directly outputting pressure against volumetric strain and stress difference against mean effective stress in a form that, within a single test, is suitable for evaluation of the parameters for hydrocode material models that can be employed in military equipment performance assessments, where triaxial compressive stresses can be significantly greater than those typically resulting from structural service loads. This paper describes specimen preparation, the test set-up, the test process and associated data capture, the theory of the stress analysis and the application of the test data to simple hydrocode material models. A database of concrete, rock and soil properties has been generated using the gauged reactive confinement (GREAC) cell and the method has also been compared with the more traditional active confinement triaxial test method. The issues of strain rate are also addressed.

The use of thick fiber reinforced polymer (FRP) laminates in composite armor and naval structures requires thorough characterization of the through-thickness properties of said laminates, both quasi-statically and at high strain rates. Specimens cut from an E-Glass/vinyl ester FRP were tested in compression both quasi-statically and dynamically using a split Hopkinson pressure bar (SHPB). The SHPB tests utilized a conical striker for pulse shaping, to reduce the variation in strain rate during the test. The quasi-static through-thickness compressive strength was 417 MPa, while the SHPB tests produced a strength of 462 MPa at an average strain rate of 5.1 × 102 s−1. A single HPB configured for spalling tests was used to determine the dynamic through-thickness tensile strength (interlaminar tension). The interlaminar tensile strength was 125 MPa at an average strain rate of 1.8 × 103 s−1.

BACKGROUND:Improvised explosive devices have become the characteristic weapon of conflicts in Iraq and Afghanistan. While little can be done to mitigate against the effects of blast in free-field explosions, scaled blast simulations have shown that the combat boot can attenuate the effects on the vehicle occupants of anti-vehicular mine blasts. Although the combat boot offers some protection to the lower limb, its behaviour at the energies seen in anti-vehicular mine blast has not been documented previously.METHODS:The sole of eight same-size combat boots from two brands currently used by UK troops deployed to Iraq and Afghanistan were impacted at energies of up to 518 J, using a spring-assisted drop rig.RESULTS:The results showed that the Meindl Desert Fox combat boot consistently experienced a lower peak force at lower impact energies and a longer time-to-peak force at higher impact energies when compared with the Lowa Desert Fox combat boot.DISCUSSION:This reduction in the peak force and extended rise time, resulting in a lower energy transfer rate, is a potentially positive mitigating effect in terms of the trauma experienced by the lower limb.CONCLUSION:Currently, combat boots are tested under impact at the energies seen during heel strike in running. Through the identification of significantly different behaviours at high loading, this study has shown that there is rationale in adding the performance of combat boots under impact at energies above those set out in international standards to the list of criteria for the selection of a combat boot.

This paper summarises experimental investigations of undamaged and partially damaged reinforced-concrete beams and columns. The aim of the work was to establish and carry out experimental methods for determining the load deformation behaviour and strength of these simple structural elements under varying levels of localised pre-damage (such as weakening or partial loss of concrete material). In particular, the effect of such partial/local damage on the overall behaviour and, crucially, its contribution to structural collapse, were also studied. There is little experimental evidence to validate predictions obtained from analysis or numerical modelling of partially damaged concrete members. Often, the ultimate capacity is the primary output of interest and it is usually determined using specimens that have no prior local damage. The present study produced data that led to a comparative study between the structural behaviour of both damaged and undamaged structural elements in order to help understand the effect of local damage and its contribution to structural collapse. The experimental results can also be used for future modelling and validation purposes. [doi: 10.1680/stco.2010.11.3.139]