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Modelling composite toughness and what mechanisms are responsible for added toughness has been less tackled within the composites community. With the advances of computational resources and the development of arbitrary cracking models, such as the Augmented Finite Element Method (AFEM), more complex microstructures can now be tackled with multiple interacting cracks. It has been established that Mode I crack propagation in particle-toughened interlayers within a CFRP laminate involve a process zone rather than a distinct crack tip. This involves multiple cracks forming ahead of the main crack that then coalesce and leave behind bridging ligaments that provide traction across the crack flanks. Preliminary idealised 2D AFEM models are presented in this work, that highlight the effects of the relative role of neat resin to ply interface cohesive properties, and the fraction of ‘idealised de-bonds’/discontinuities, in keeping the crack path within the interlayer. 4- dimensional time-resolved Computed Tomography (CT) experiments complement the abstract models, with the chronology of damage events and resultant crack paths being directly identified in different toughened microstructures. Additionally, quantification of the bridging behaviour elucidated micromechanical differences between the systems, with the number of bridging ligaments and the total bridged area being quantified and compared to macro-scale toughness. This work is intended to improve understanding around interlaminar toughness, and lead to the development and validation of physically representative micro-mechanical models

The time course of cardiac sympathetic nerve activity (CSNA) following acute myocardial infarction (MI) is unknown. We therefore undertook serial direct recordings of CSNA, arterial blood pressure (MAP) and heart rate (HR) in 11 conscious sheep before and after MI, and compared them with 10 controls. Conscious CSNA recordings were taken daily from electrodes glued into the thoracic cardiac nerves. Infarction was induced under pethidine and diazepam analgesia by applying tension to a coronary suture. MI size was assessed by left ventricular planimetry (%) at postmortem, peak troponin T and brain natriuretic peptide levels (BNP). Baroreflex slopes were assessed daily using phenylephrine-nitroprusside ramps. The mean infarcted area was 14.4 ± 2.9%, troponin T 1.88 ± 0.39 μg l−1 and BNP 8.4 ± 1.3 pmol l−1. There were no differences in haemodynamic parameters or CSNA between groups at baseline. MAP and HR remained constant following MI. CSNA burst frequency increased from baseline levels of 55.8 ± 7.1 bursts min−1 to levels of 77.5 ± 8.7 bursts min−1 at 2 h post-MI, and remained elevated for 2 days (P < 0.001). CSNA burst area also increased and was sustained for 7 days following MI (P= 0.016). Baroreflex slopes for pulse interval and CSNA did not change. CSNA increases within 1 h of the onset of MI and is sustained for at least 7 days. The duration of this response may be longer because the recording fields decrease with time. This result is consistent with a sustained cardiac excitatory sympathetic reflex.

The progression of damage in a hybrid composite-metallic structure subject to out-of-plane loading has been examined throughout an interrupted quasi-static-indentation test using micro-focus computed tomography for damage assessment. Two key damage events were identified from the load displacement tests. The CT data shows that the first damage mechanisms to occur are yielding of the aluminum substrate and matrix cracking in the CFRP; the onset of these damage mechanisms occurs at a similar point in the loading process. With increasing load, delamination occurred between all plies in the CFRP layer. The bonded interface between the aluminum and CFRP was maintained at lower loads - a crack initiated preferentially within the innermost CFRP ply rather than at the interface between the two materials. The CT data indicates that the second damage event on the load displacement curve can be attributed to CFRP fibre fracture, consistent with contact forces. This work indicates that relatively low-level out-of-plane loads are likely to cause plastic deformation to the aluminum substrate, whilst the integrity of the fibre in the CFRP is maintained until higher loads.

Cardiac sympathetic nerve activity (CSNA) is of major importance in the etiology of heart disease but is impossible to measure directly in humans. Ovine and human cardiovascular systems are similar; therefore, we have developed a method for the daily recording of CSNA in conscious sheep. After thoracotomy, electrodes were glued into the left thoracic cardiac nerve and CSNA, blood pressure (BP), and heart rate were recorded daily. Satisfactory recordings ≥7 days of CSNA were obtained in 11 of 28 sheep (40%), mean recording time 10.6 days, range 7-47. During the first week, CSNA decreased gradually from 78 ± 8 at baseline to 60 ± 7 bursts/min on day 5( P = 0.02) or from 76 ± 9 to 57 ± 7 bursts/100 beats on day 7 ( P = 0.04). Similarly, BP decreased from 103 ± 4 to 94 ± 4 mmHg ( P = 0.03). Low-frequency heart rate variability decreased from 0.12 ± 0.02 to 0.06 ± 0.02 ms2on day 6 ( P = 0.004) but was not correlated to CSNA. In conclusion, CSNA that can be continually recorded in conscious sheep decreases during the first week postsurgery and, thereafter, stabilizes. This model should provide valuable insights in future investigations of cardiac disease.

Mode I and Mode II crack growth through particle-toughened CFRPs (Carbon Fibre Reinforced Plastics) have been captured using in situ and ex situ Synchrotron Radiation Computed Tomography (SRCT) and Synchrotron Radiation Computed Laminography (SRCL). These experiments were used to provide non-destructive identification of fracture mechanisms at representative stress states for two different material geometries. The local micro-structure prior to crack propagation, the location of particle/matrix de-bonding events, the formation of bridging ligaments, and the evolution of the resultant crack path was identified and related to the local micro-structure. Such data is invaluable to the development and validation of physically representative micro-mechanical models for these material systems that are increasingly being used in primary aerospace structures.

This work investigates the micromechanisms associated with particle-toughening strategies to improve the damage resistant and damage tolerant performance in carbon fibre reinforced polymer (CFRP) materials. Five material systems were studied; consisting of one untoughened and four particle-toughened systems. Synchrotron radiation computed tomography (SRCT) was used to study the damage micromechanisms in standard 150mm x 100 mm rectangular coupons subjected to 30 J low velocity impact loading. Laboratory based micro-focus computed tomography (?CT) enabled damage assessments and comparison of coupons subjected to low velocity impact, quasi-static indentation and at the onset of compression-after-impact failure. Mechanisms leading to damage resistance and damage tolerance are discussed along with strategies to use these observations to inform finite element models.

In the pathophysiological study of vasovagal syncope, the nature of the interaction between baroreceptor sensitivity (BS), sympathetic withdrawal, and parasympathetic activity has yet to be ascertained. Altered BS may predispose toward abnormal sympathetic and parasympathetic responses to orthostasis, causing hypotension that may progress to syncope if there is sympathetic withdrawal. To examine this hypothesis, we monitored blood pressure (BP), heart rate (HR), BS, forearm blood flow, and muscle nerve sympathetic activity (MNSA) continuously in 18 vasovagal patients during 60° head-up tilt, syncope, and recovery. Results were compared with those of 17 patients who were able to tolerate tilt for 45 min. During early tilt, BP was maintained in both groups by an increase in HR and MNSA from baseline ( P < 0.01), but BS decreased more in the syncopal group ( P < 0.05). At the start of presyncope (mean 2.7 ± 0.2 min before syncope and 15.2 ± 12 min after tilt), when BP fell, HR and sympathetic activity remained increased from baseline ( P< 0.01). Thereafter, BP and HR correlated directly with sympathetic activity and regressed in linear fashion until syncope ( P < 0.001), whereas BS increased to baseline. At syncope, BP, HR, and sympathetic activity fell below baseline ( P < 0.01, P < 0.05, and P < 0.01, respectively), but BS did not increase. During recovery, sympathetic activity increased to baseline and BS increased ( P < 0.05), whereas HR and BP remained low ( P < 0.01 and P < 0.05, respectively). The mechanism for the initiation of hypotension during presyncope remains unknown, but BS may contribute. Vasodilatation and bradycardia during presyncope appear to be more closely related to withdrawal of sympathetic activity than to increased parasympathetic cardiac activity.

In a controlled study, 26 patients with a history of recurrent syncope were found to have increased arginine vasopressin, corticotrophin, and atrial natriuretic factor levels after 5 minutes of 60 degrees head-up tilt, long before they became hypotensive. The exaggerated neurohormonal response in these patients may indicate a greater sensitivity to central hypovolemia which may predispose to vasovagal syncope, mediated by the vasodilatory effects of atrial natriuretic factor or the sensitization of mechanoreceptors by arginine vasopressin.

In this study interrupted quasi-static indentation and post-impacted compression tests were performed at incremental load steps with X-ray computed tomography performed at each step. This enabled non-destructive, three-dimensional damage assessments to be carried out allowing initiation and propagation of different damage modes to be monitored. Preliminary results from these experiments are reported in this paper.

Synchrotron Radiation Computed Tomography (SRCT) allows for non-destructive identification of fracture mechanisms in materials at very high resolutions. In this work, carbon fibre reinforced plastics (CFRPs) were imaged using SRCT to ascertain fracture micro-mechanisms under both quasi-static Mode I and Mode II dominated loading conditions. This, combined with previous work on impacted coupons, provides mechanistic comparison between the different loading conditions on similar material systems. Initial findings have identified particle/matrix debonding, crack bridging and ligamented behaviour as reported previously, but have emphasized micro-cracks and the extent to which particle/matrix debonding occurs ahead of the crack tip under both Mode I and Mode II loading conditions. Such work is intended to support both material development and more accurate structural performance simulation for the toughened materials that are being increasingly used as primary structures in aerospace applications.

Pure vasodilator drugs are currently the preferred agents for treatment of acute and chronic heart failure of all grades of severity. In contrast, the role of drugs that combine vasodilation with inotropic action remains highly controversial despite their several advantageous physiological actions and long therapeutic history in heart failure. We hypothesize that this uncertainty might be due first to subtle unfavorable hemodynamic effects not detectable by the relatively crude hemodynamic methods by which these agents are usually analyzed, particularly with regard to the quantification of afterload, and secondly to the narrow therapeutic range of these drugs, such that the dose administered is critical. We tested this hypothesis by comparing several refined hemodynamic measurements of dopexamine, an inotropic vasodilator, with a pure arteriovenous dilator (sodium nitroprusside, SNP) on left ventricular (LV) systolic and diastolic function, large arterial behavior, and coupling of the left ventricle to the arterial system at two dose levels in 35 patients with ischemic heart disease. The study protocol was a fixed order of 15-min infusions of saline, dopexamine 1 microg/kg/min, and dopexamine 3 + ++microg/kg/min, or saline, SNP 1 microg/kg/min, and SNP 3 microg/kg/min. Detailed hemodynamic observations were made at the end of each 15-min infusion period. Both drugs produced equivalent arterial vasodilation, as measured by the decrease in systemic vascular resistance index (SVRI), but dopexamine resulted in a significantly greater increase in cardiac index (CI). Myocardial contractility, assessed by several load-independent indexes, increased with dopexamine, as anticipated with an inotropic drug, but did not alter with SNP. Arterial compliance, a measure of the distensibility of large conduit arteries, was increased by SNP but not by dopexamine. Arterial wave reflection was increased by dopexamine, especially at high doses, but reduced by SNP. Increased arterial compliance and reduced wave reflection reduce LV afterload. SNP reduced preload, whereas dopexamine had no effect on this aspect of ventricular function. Vasodilator drugs and those which combine vasodilator and inotropy increase cardiac output (CO) and reduce SVR. Therapy with inotropic vasodilators has no effect on preload and does not reduce the dynamic components of ventricular afterload, although it does reduce its static components. These effects are dose dependent; there is less perturbation of afterload at lower doses. In contrast, vasodilator therapy reduces preload and both static and dynamic parts of afterload.

3D X-ray computed tomography (CT) was used to study the effects of particle toughening within unidirectional carbon fibre reinforced polymer (CFRP) materials subjected to impact damage, followed by ex situ CT of compression after impact (CAI) tests at incremental loads. A multi-scale approach utilizing synchrotron radiation CT and laminography was used to study the damage micro-mechanisms of impact-loaded specimens, and micro-focus CT (?CT) assessed damage at meso- and macro-scopic levels. For the ex situ compression after impact testing, plates were CT scanned after progressively larger compressive loads were applied. Particle toughening processes were observed, with damage growth and micro-buckling events being captured close to the final failure in the CAI test.

International audience; On présente dans cette étude la discrimination des phénomènes de ruptures de fibre, de microfissuration intralaminaire, de macrofissuration intralaminaire ainsi que du microdélaminage au sein des composites stratifiés d'unidirectionnels orientés, dans le cadre d'une méthode de détection des endommagements basée sur la technique de l'Emission Acoustique. Ces résultats expérimentaux sont confrontés aux prévisions issues d'un modèle de comportement de matériaux composites unidirectionnels, basés sur la physique des phénomènes à l'échelle des constituants.

This project focuses on the consequences of decisions to reunify children who had entered the looked-after system for abuse or neglect. It compares the progress and outcomes of a sample of maltreated children who either went home or remained in the looked-after system.

Laminated fibre reinforced polymer composite materials are increasingly being applied within critical structures, with a corresponding demand for reliable damage prediction tools to reduce the time and cost associated with product development. The present work is carried out to underpin the evolution of micromechanically-based models by providing developers with a resource of 4D (time & spatially resolved) microstructural and micromechanical data obtained from high-resolution synchrotron radiation computed tomography of essentially standard materials. The intention is to share data with the composites community as part of the public materials data repository that is currently being developed within the University of Southampton’s School of Engineering Sciences. Testing was conducted at the European Synchrotron Radiation Facility (ESRF) during in-situ loading of [90/0]s laminate in both small tensile coupon and larger plate forms. Image processing has been used to visualize the evolution of transverse ply cracks, longitudinal splits, inter-ply delaminations and associated interactions. Methods for full-field and full-volume crack displacement (e.g. mode I & II opening) are discussed.

National audience; A model to predict fibre break accumulation that takes into account all physical phenomena at the origin of the fibre break (i.e. the random nature, stress transfer due to breaks, fibre debonding and viscosity of the matrix) shows clearly that the failure of a unidirectional composite structure results in the formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. The object of the study is to experimentally confirm this scenario. Many techniques exist to detect the failure of carbon fibre composites, however none of them offer a resolution that allows this goal to be achieved in a non-destructive manner and in three dimensions. High resolution computed tomography has been used to confirm the scenario modelled. A sample was tested and observed in-situ at the European Synchrotron Research Facilities, ESRF, Grenoble. All fibre breaks arising in the vicinity of the final rupture of a unidirectional composite have been detected and the formation of clusters can be observed.

International audience; Fracture toughness anisotropy of AA2139 (Al-Cu-Mg) in T351 and T8 conditions has been investigated via mechanical testing of smooth and notched specimens of different geometries, loaded in the rolling direction (L) or in the transverse direction (T). Fracture mechanisms were investigated via SEM and synchrotron radiation computed tomography (SRCT). Contributions to failure anisotropy are identified with: (i) anisotropic initial void shape and growth, (ii) plastic behaviour including isotropic/kinematic hardening and plastic anisotropy, and (iii) nucleation at a 2nd population of 2nd phase particles leading to coalescence via narrow crack regions. A model based in part on the Gurson-Tvergaard-Needleman approach is constructed to describe and predict deformation behaviour, crack propagation and, in particular, toughness anisotropy. Model parameters are fitted using microstructural data and data on deformation and crack propagation for a range of small test samples. Its transferability has been shown by simulating tests of large M(T) samples.

Many adaptive numerical modelling (ANM) techniques such as artificial neural networks, (including multi-layer perceptrons) support vector machines and Gaussian processes have now been applied to a wide range of regression and classification problems in materials science. Materials science offers a wide range of industrial applications and hence problem complexity levels from well physically characterised systems (e.g. high value, low volume products) to high volume low cost applications with intrinsic scatter due to commercial manufacturing processes. We review a number of recent examples in the literature, with the aim of identifying best practice in the use of these techniques as part of a multi-strand modelling approach. The importance of understanding the basic principles of these modelling techniques and how they can link with other modelling strategies is emphasised. In particular we wish to identify the importance of hybrid physically based-ANM in taking the field forward, which can range from, at the most basic level, careful data selection and data pre-processing to a full integration of physically based models with advanced ANM. A number of case studies are presented to illustrate the main points of the paper.

International audience; no abstract

International audience

The present work applies a model for microstructural evolution in the solid state and Al-Cu-Mg alloys and expands it in a computationally efficient way to include solid-liquid reactions in fusion welds. The model is used to predict local strength and hardness of the welds, using a formulation that incorporates hardening due to two types of precipitates i.e. Cu-Mg co-clusters and the S phase precipitates. The model predictions are compared with hardness, differential scanning calorimetry and transmission electron microscopy data for a fusion welded 2024-T351 aluminium alloy. The model predicts solid state reactions and solid-liquid reactions including co-cluster dissolution, S phase formation, growth, coarsening and dissolution, co-cluster reformation on cooling, and solute partitioning on re-solidification. The model predictions are in good agreement with the experimental results and illustrate the dominant role that (sub-) nano scale co-clusters play in strengthening of welds. The yield strength of as-welded material tested normal to the weld is mainly due to the co-clusters.

The friction stir welding process has been used to join 13mm gauge 2024-T351 aluminium alloy plates together. A detailed microstructural study of the resulting weld was carried out using Differential Scanning Calorimetry (DSC), hardness testing, Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD). DSC was used to explain the hardness results at a number of regions across the weld in terms of co-cluster dissolution and reformation and S phase formation, coarsening and dissolution. The “onion rings” structure found in the nugget weld was shown to be the result of a combination of the slight grain size variations and a change in nature and size of the particles present (i.e. intragranular versus intergranular). The variation in corrosion properties and hardness of the rings is discussed in terms of the local microstructure and quench sensitivities.

Analysis of toughness in 6156 Al-Mg-Si-Cu sheet has been performed using enhanced Kahn tear tests on samples quenched at different rates, whilst microstructures of the samples have been assessed using differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Crack initiation energies were unaffected by changing water quench temperature from 20°C to 60°C, however a significant reduction was evident on air cooling. Crack propagation resistance was reduced for both 60°C water quenched and air cooled materials. The failure morphology of the air cooled material appears consistent with classical intergranular ductile failure. Coarse voiding and shear decohesion was prevalent in the 20°C water quenched material, whilst the 60°C water quenched material showed a mixture of transgranular and intergranular fracture modes. Changes in microstructure and precipitation behaviour resulting from reduced quenching rate were identified and related to the observed fracture behaviour, particularly in terms of precipitate free zone formation and the simultaneous presence of coarse particles at grain boundaries.

This paper was written shortly after the publication of the Laming Report and before the publication of Every Child Matters. Much that has happened since then has addressed the concerns we raised. To bring the paper up to date with these developments would require rewriting it altogether. That said, it is, perhaps, not merely of historical interest. Those reading it may like to consider two issues. First, how far have services in fact moved to address the concerns we outline? Second, how far do services continue to be dogged by an unrealistic desire to eliminate risk? Insofar as the paper prompts these reflections, it will have met its authors' aims.

A model has been developed to predict short crack fatigue life in the fusion zone of Metal Inert Gas (MIG) welded 2024-T351, based on the observed propensity for complex, multiple cracking processes in this region. To initiate cracks, a Monte-Carlo method has been used, based on the probability of initiation at interdendritic defects derived from the experimental observations. Short crack propagation simulation has been achieved via a microstructurally sensitive approach using continuous dislocation distribution methods. Different geometrical conditions to define crack shielding or crack coalescence have also been identified, along with a first order estimate of crack closure effects and associated influences of residual stress on crack growth. In the regime of specific interest here (crack growth to 1mm total length), good correlation is shown between measured and predicted fatigue performance.

Age forming of lower wing skin structures for civil airframes requires an alloy with good age formability and mechanical properties (yield strength, ultimate tensile strength, fatigue resistance, toughness). Using property modelling and general metallurgical understanding, a series of Al-Cu-Mg-Li (Mn, Zr, Sc) alloys have been designed. After artificial ageing representative of age-forming several of the newly designed alloys have yield strength, fatigue crack growth resistance and toughness that are at least comparable to the incumbent damage tolerant material for such applications, viz. 2024-T351. Coarse grain structure and high Li content are seen to be associated with good fatigue resistance but reduced formability, and an optimum balance needs to be sought.

The importance of cardiac output (CO) to blood pressure level during vasovagal syncope is unknown. We measured thermodilution CO, mean blood pressure (MBP), and leg muscle mean sympathetic nerve activity (MSNA) each minute during 60° head-up tilt in 26 patients with recurrent syncope. Eight patients tolerated tilt (TT) for 45 min (mean age 60 ± 5 yr) and 15 patients developed syncope during tilt (TS) (mean age 58 ± 4 yr, mean tilt time 15.4 ± 2 min). In TT patients, CO decreased during the first minute of tilt (from 3.2 ± 0.2 to 2.5 ± 0.3 l · min−1 · m−2, P = 0.001) and thereafter remained stable between 2.5 ± 0.3 ( P = 0.001) and 2.4 ± 0.2 l · min−1 · m−2( P = 0.004) at 5 and 45 min, respectively. In TS patients, CO decreased during the first minute (from 3.3 ± 0.2 to 2.7 ± 0.1 l · min−1 · m−2, P = 0.02) and was stable until 7 min before syncope, falling to 2.0 ± 0.2 at syncope ( P = 0.001). Regression slopes for CO versus time during tilt were −0.01 min−1 in TT versus −0.1 l · min−1 · m−2 · min−1in TS ( P = 0.001). However, MBP was more closely correlated to total peripheral resistance ( R = 0.56, P = 0.001) and MSNA ( R = 0.58, P = 0.001) than CO ( R = 0.32, P = 0.001). In vasovagal reactions, a progressive decline in CO may contribute to hypotension some minutes before syncope occurs.

Fatigue failure characteristics of friction stir welds in 13mm gauge 2024-T351 plate have been assessed. Failure occurred from either the weld region (nugget/flow arm) or from the material immediately surrounding the weld. Fatigue failure from the surrounding material was essentially conventional, initiating from large S-phase intermetallic particles and growing in a macroscopic mode I manner. Corresponding fatigue lives were seen to be comparable to parent plate and results previously reported for similar welds in thinner plate. Failure over the weld region was identified with discontinuities in the macroscopic flow pattern of the weld flow arm. Subsequent crack growth showed pronounced macroscopic crack deflection around the ‘onion ring’ structure of the weld nugget. The bands making up the onion rings were identified with variations in local hardness levels, consistent with a mechanical contribution to the crack deflection process.

A 48-year-old woman presented with a history of progressive cough, dysphonia, dysphagia, and postural symptoms. Subsequent neurological investigations were consistent with a bilateral vagal mononeuropathy, and neurosarcoidosis was diagnosed after scalene node biopsy. Autonomic investigations including microneurography, neurohormones, and heart rate variability demonstrated arterial and cardiopulmonary baroreflex failure. In addition, parasympathetic control of heart rate was absent and consistent with a bilateral, nonselective lesion in the proximal vagus.

The development of grain size during commercial thermomechanical processing of 6000 series aluminium alloy components has been investigated by combining physical experiments and modelling techniques. A range of grain structures was generated by varying both deformation temperature and heat treatment practice. The different deformation conditions were simulated by finite element modelling, which allowed parameters such as plastic strain, strain rate and deformation temperature to be subsequently extracted. An adaptive numeric technique (neurofuzzy modelling) was employed to describe the recrystallized grain size in terms of the process parameters, and its performance compared with that of an empirical relationship from the literature.

The incidence of roughness induced fatigue crack closure has been studied by finite element modelling.Results show an increasing effect of crack path angle on closure levels with the closure mechanism being strongly dependent on residual plastic strains in the wake rather than global shear displacements of the fracture surfaces.An analytical expression for the functional dependence of roughness induced closure has been produced which shows reasonable agreement with the finite element results.

The paper deals with the application of multiple linear regression and neurofuzzy modelling approaches to 7xxx series based aluminium alloys. 36 compositional and ageing time variants and subsequent proof strength and electrical conductivity measurements have been studied. The input datasets have been transformed in two ways: to reveal more explicit microstructural information and to reflect some empirical findings in the literature. Neurofuzzy modelling exhibited improved performance in modelling proof strength and electrical conductivity cf. the multiple linear regression approach. Electrical conductivity is best modelled using the explicit microstructural input dataset, whilst proof strength is best modelled by a further modification of this dataset, decided upon after inspection of the subnetwork structures produced by neurofuzzy modelling. Neurofuzzy modelling offers a transparent empirically based data-driven approach that can be combined with pre-processing of the data and initialising of the model structure based upon physical understanding. An iterative modelling approach is defined whereby data-driven empirical modelling approaches are first used to assess underlying data structures and are validated against physically based understanding, these then inform subsequent initialised neurofuzzy models and input data transformations to provide both optimal subset and feature representation.