Greater Strain Research Articles

Electro-hydraulic forming of sheet metals: Free-forming vs. conical-die forming

This work builds upon our recent advances in quantifying high-rate deformation behavior of sheet metals, during electro-hydraulic forming (EHF), using high-speed imaging and digital image correlation techniques. Aluminum alloy AA5182-O and DP600 steel sheets (1mm thick, ∼152mm diameter) were EHF deformed by high-energy (up to ∼34kJ) pressure-pulse in an open die (free-forming) and inside a conical die. The deformation history (velocity, strain, strain-rate, and strain-path) at the apex of the formed domes was quantified and analyzed. The data shows that the use of a die in the EHF process resulted in an amplification, relative to free-forming conditions, of the out-of-plane normal velocity and in-plane strain-rate at the dome apex. This amplification is attributed to the focusing action of the die on account of its conical geometry. Further, while the strain-path at the dome apex was generally linear and proportional, the use of a die resulted in greater strain at the apex relative to the strain during free-forming. The sheet deformation profile in the EHF process was found to be different from that previously observed in electromagnetic forming (EMF) and, thus, the two processes are expected to result in different strain-paths and formability. It is anticipated that quantitative information of the sheet deformation history, made possible by the experimental technique developed in this work, will improve our understanding of the roles of strain-rate and sheet–die interactions in enhancing the sheet metal formability during high-rate forming.

Shear mediated elongational flow and yielding in soft glassy materials

In this work, we study the deformation behavior of thin films of various soft glassy materials that are simultaneously subjected to two creep flow fields, rotational shear flow by applying torque and elongational flow by applying normal force. The generic behavior under the combined fields is investigated in different soft glassy materials with diverse microstructure such as: hair gel, emulsion paint, shaving foam and clay suspension. Increase in strength of one stress component while keeping the other constant, not only leads to an expected enhanced deformation in its own direction, but also greater strain in the other direction. Herschel Bulkley model is observed to explain this behavior qualitatively. Elongational flow induced in the materials eventually causes failure in the same. Interestingly time to failure is observed to be strongly dependent not just on normal force but also on the applied rotational shear stress. We believe that the presence of a three dimensional jammed structure, in which overall unjamming can be induced by applying stress having sufficient magnitude irrespective of the direction leads to the observed behavior. In addition, we observe self-similarity in the elongational as well as rotational strain time curves corresponding to various combinations of both the fields. This observation suggests a mere shift in the time-scales involved keeping the path followed in the process unchanged. A phase diagram is also constructed for various soft glassy materials by determining different combinations of orthogonal stresses beyond which materials yield. Estimated yield stress in the limit of flow dominated by applied tensile force on the top plate demonstrates scatter, which might be originating from fingering instability. Except this deviation, yielding is observed when the invariant of stress tensor exceeds yield stress, validating the Von Mises criterion.

The Study of Field Effect through Uniaxial Compression Experiment on Marine Recycled Concrete Specimen Based on DPDM Technique

Recycled concrete is a kind of composite heterogeneous material. Through the uniaxial compression experiment on recycled concrete specimen, the corresponding stress-strain curve is depicted with the major variables of replacement rate of recycled aggregate and time of corrosion by seawater, and the analysis of compression resistance capacity of recycled concrete sample is carried out by comparing common samples with those after the process of vacuum pumping. According to the results of comparison, the process of vacuum pumping can raise the strength of concrete by 9% to 22% and the lowering speed of compression resistance capacity rises as replacement rate of recycled aggregate goes up after the same corrosion period. The compression resistance capacity of the concrete specimen with replacement rate of 60% descends 50% to 80% faster than the sample with 30% of rate. DPDM technique is used to analyze deformation field, displacement field and strain field of concrete specimen during the process of uniaxial compression. As shown in the images from the experiment, the cracks develop from the bottom and both edges towards the middle part along the direction of loading until some of them run through the cube with the failure of the overall specimen while the stress reaches the peak, the displacement amount decreases from bottom to top and from both edges to center and the greatest strain concentration scatters around the bottom of the specimen while the strain of 62% appears around the peak stress of 33-36MPa. This paper puts forward constructive references and guidance for the application of recycled concrete in marine engineering on the basis of the study of field effect through uniaxial compression experiment based on DPDM technique.

Evaluation of a Brief Intervention to Improve the Nursing Care of Young Children in a High HIV and AIDS Setting

The HIV epidemic in South Africa is putting great strain on health services, including the inpatient care of young children. Caregivers and young children (107 pairs) and 17 nurses participated in an intervention to improve the care of young children in hospital in a high HIV and AIDS setting. The intervention addressed caregiver expectations about admission and treatment, responsive feeding, coping with infant pain and distress, assistance with medical procedures, and preparation for discharge and home care. Following a preparatory and piloting phase, measures of nurse burnout, caregiver physical and emotional well-being, and caregiver-child interaction were made before and after intervention. No changes were found between before and after intervention on assessments of caregiver wellbeing. However, mothers in the postintervention phase rated nurses as more supportive; mother-child interaction during feeding was more relaxed and engaged, and babies were less socially withdrawn. While the intervention proved useful in improving certain outcomes for children and their caregivers, it did not address challenging hospital and ward administration or support needed by caregivers at home following discharge. To address the latter need, the intervention has been extended into the community through home-based palliative care and support.

The impact of advanced practice nursing in healthcare: recipe for developing countries.

The increasing demand for healthcare services on all levels is placing great strain on healthcare systems throughout the world. Escalating demands combined with a shortage of General Practitioners (GPs) have forced politicians in many countries to reevaluate the distribution of work tasks and areas of responsibility between different healthcare personnel.1,2 Registered nurses’ (RN) roles and scope of practice have been expanded in many countries and the quality and cost-effectiveness of healthcare systems have improved.2,3 For example, a private nurse practitioner-run clinic opened in Brisbane, Australia4 in September 2011 with the aim to shorten patient waiting times for basic healthcare needs; in most parts of the world RNs now comprise the largest group of healthcare providers.

Introduction: Household Finances under Pressure: What is the Role of Social Policy?

This themed issue examines household finances within the context of the 2007 banking crisis, which triggered the biggest downturn in many global economies since the Great Depression in the 1930s. The effects of this crisis and subsequent global recession were still unfolding at the time the articles of this issue were submitted to the journal. The election of the coalition government in May 2010, and its emergency budget aimed at reducing the nation's budget deficit, precipitated the biggest reduction in public sector funding in living memory. Rising unemployment and the increasing cost of living means that for many households even greater strain has been placed on their finances. Other developments, such as the winding-up of the Treasury Financial Inclusion Taskforce and the axing of asset building policies, for example the Child Trust Fund and Saving Gateway, had, to some, signalled an end to the consensus in government that had been built up around the financial inclusion agenda, and had left a big gap in social policy.

An experimental investigation of the interactions between reaction-driven and stress-driven melt segregation: 2. Disaggregation at high melt fraction

To investigate the coupling between stress-driven melt segregation and reaction-driven melt infiltration, we performed static annealing and torsional deformation experiments on couples constructed from a melt-rich basaltic source and melt-poor olivine + orthopyroxene + chromite + basalt sink. In this study (the second of two companion papers), the melt source is almost completely molten with ϕ = 0.8–0.9, well above the rheologically critical melt fraction. We deformed two geometries of source/sink couples with the source either as the core or the outer ring of a cylinder. Our experiments demonstrate (1) that deformation significantly enhances the rate of melt infiltration from the source into the sink and (2) that combined reaction and deformation promote greater strain localization than does deformation alone. Deformation and melt infiltration enhance disaggregation at the interface of the source and sink. The implication of these coupled interactions is that deformation and melt-rock reaction may enhance the corrosion (or ‘stoping’) rates of the wall rocks of magma chambers and intrusions in the crust and upper mantle.

Foreword: Vulnerable populations in the Arctic

Interest in the Arctic has grown significantly in recent years. The Arctic environment is unique and highly sensitive to disturbances. Temperatures have already risen twice as quickly in the Arctic as elsewhere on Earth. Glaciers and sea ice are melting more extensively than in the past. This is already putting a great strain on communities and ecosystems. As ice withdraws, technological advances are creating opportunities to open transport routes across the Arctic Ocean and exploit the natural resources of the Arctic. These developments must be managed in a responsible and sustainable manner so that they do not lead to undesired effects. (Published: 22 November 2011) Citation: Global Health Action 2011, 4 : 11132 - DOI: 10.3402/gha.v4i0.11132

Airport capacity utilization in Nigeria: A performance and efficiency analysis

Most airlines in Nigeria fly at about the same time of the day creating great strains on airports’ runways and air traffic management. This study examines air traffic flow: recorded landings and take-offs times, arrival times and time between arrivals and times spent in the airport. The data collected were analyzed using the queue theory to know the airport turnaround time and the rate of usage of the airport as well as time variation in usage pattern. The results showed that the airport was grossly underutilized; most domestic traffic movements had two main peaks (morning and evening) with the headway been dangerously close. There is grave danger in clustered take-offs and landings so it was advised that to boost airport capacity utilization staggering of airlines’ schedules should be encouraged.

Revisiting dirt cracking as a physical weathering process in warm deserts

A half century ago C.D. Ollier proposed that insolation-driven temperature changes expand and contract fill in fissures enough to widen cracks, a process that would permit progressively deeper penetration of fissure fills, that would in turn generate a positive feedback of greater and greater strain until desert boulders and bedrock shatters. Although desert physical weathering by “dirt cracking” has occasionally been cited, this hypothesized process remains without support from subsequent research. Here, field observations, electron microscopy, X-ray powder diffraction, particle-size analysis, and laboratory experiments shed new light on dirt cracking. Little clear evidence supports the original notion of expansive pressures from thermal fluctuations. However, mineralogical, high resolution transmission electron microscopy, back-scattered electron microscopy, and experimental evidence support two alternative processes of widening fractures: wetting and drying of fills inside fissures; and the precipitation and remobilization of calcium carbonate. A re-envisioned dirt-cracking wedging process starts with calcium carbonate precipitating in fissures less than 5 μm wide. First precipitation, and then ongoing dissolution of this laminar calcrete, opens enough space for dust to penetrate into these narrow fractures. Wetting of expansive clays in the fissure fill exerts enough pressure to widen and deepen the fissure, allowing the carbonate precipitation process to penetrate even deeper and allowing even more dust to move into a fracture. As the dust infiltrates, its texture changes from a chaotic mix of particles to an alignment of clays parallel to fissure sides. This parallel alignment could increase the efficiency of fill wedging. Ollier's concept of a positive feedback remains supported; each increment of fracture deepening and widening permits more, even deeper infiltration of laminar calcrete and dust. Field and electron microscope observations of rock spalling in the winter of 2010 are consistent with Ollier's hypothesis that dirt cracking is a common physical weathering process in deserts that splits rocks of all different sizes.

Legal Aid and Legal Expenses Insurance, Complements or Substitutes? The Case of the Netherlands

The budget of the Dutch Ministry of Justice is under great strain. Quite recently, the budget for legal aid (some € 450 million in total) has been critically reviewed in order to save € 50 million in the next few years. One of the main savings proposed was to discontinue subsidized legal aid for non-criminal cases for all but the lowest income groups and to refer the citizens involved to private legal expenses insurance (LEI). This proposal did not receive much public support and has been put aside for the time being. But on the next occasion it is quite likely to reappear on the political agenda. Given the present state of affairs, it seems wise to study the interrelationship between legal aid and LEI. Is LEI a system that is only relevant to the high income groups which are not eligible for subsidized legal aid? Is it therefore a complement to legal aid? Or is LEI also of interest to lower income groups, and can it serve as a substitute? Our paper provides an empirical study of the interrelationship between legal aid and LEI in the Netherlands at present. It uses the results of the second wave of the Dutch Paths to Justice survey held in the first quarter of 2009. We first analyze how the holdership of LEI policies is distributed among the population in general and among income classes in particular. We then discuss how the incidence of justiciable problems interrelates with the possession of LEI. Next, we study how the possession of LEI affects the responses to justiciable problems. Do people take action? Do they seek legal advice? And from which sources? Finally, we take a look at the results. Comparing the respondents with and without LEI in various income classes, we try to answer the central question: complement or substitute? We conclude that a shift from legal aid to LEI has some clear disadvantages for low income citizens, but these may well be compensated for by some important advantages, brought to the fore by our empirical data.

Strains across the Acetabular Labrum during Hip Motion

Background Labral tears commonly cause disabling intra-articular hip pain and are commonly treated with hip arthroscopy. However, the function and role of the labrum are still unclear. Hypotheses (1) Flexion, adduction, and internal rotation (a position clinically defined as the position for physical examination known as the impingement test) places greatest circumferential strain on the anterolateral labrum and posterior labrum; (2) extension with external rotation (a position clinically utilized during physical examination to assess for posterior impingement and for anterior instability) places significant circumferential strains on the anterior labrum; (3) abduction with external rotation during neutral flexion-extension (the position the extremity rests in when a patient lies supine) places the greatest load on the lateral labrum. Study Design Descriptive laboratory study. Methods Twelve cadaveric hips (age, 79 years) without labral tears or arthritis were studied. Hips were dissected free of soft tissues, except the capsuloligamentous structures. Differential variable reluctance transducers were placed in the labrum anteriorly, anterolaterally, laterally, and posteriorly to record circumferential strains in all 4 regions as the hip was placed in 36 different positions. Results The posterior labrum had the greatest circumferential strains identified; the peak was in the flexed position, in adduction or neutral abduction-adduction. The greatest strains anteriorly were in flexion with adduction. The greatest strains anterolaterally were in full extension. External rotation had greater strains than neutral rotation and internal rotation. The greatest strains laterally were at 90° of flexion with abduction, and external or neutral rotation. In the impingement position, the anterolateral strain increased the most, while the posterior labrum showed decreased strain (greatest magnitude of strain change). When the hip is externally rotated and in neutral flexion-extension or fully extended, the posterior labrum has significantly increased strain, while the anterolateral labrum strain is decreased. Conclusion These are the first comprehensive strain data (of circumferential strain) analyzing the whole hip labrum. For the intact labrum, the greatest strain change was at the posterior acetabulum, whereas clinically, acetabular labral tears occur most frequently anterolaterally or anteriorly. The results are consistent with the impingement test as an assessment of anterolateral acetabular labral stress. The hyperextension-rotation test, often used clinically to assess anterior hip instability and posterior impingement, did not show a change in strain anteriorly, but did reveal an increase in strain posteriorly. Clinical Relevance Although this study does not include muscular forces across the hip joint, it does provide a clue as to the stresses about the labrum through the complete range of motions of the hip, which may help in providing a better understanding of the cause of labral tears and in the protection of labral repairs.

Mechanics of Pressure-Adaptive Honeycomb

Pressure-adaptive honeycomb is a new type of adaptive structure that can exhibit great strains by relying on a pressure differential to alter the structural stiffness. The structure consists of a grid of honeycomb cells that extend a significant length perpendicular to the plain of the hexagons. Each cell possesses a pouch that can be pressurized and alter the stiffness of the structure. An analytical model is presented that predicts the stress—strain behavior in principal directions of this pressure-adaptive honeycomb. The predictions of the analytical model are shown to correlate well to experimental tests on a 130-cell aluminum honeycomb specimen that is loaded up to compressive strains of 12.5%. Based on this model, an equivalent material stiffness is defined for the honeycomb cell walls that can be employed in a FEA. An FE approximation of a 145-cell honeycomb beam based on this equivalent material stiffness is shown to correlate well to experimental results of a three-point bend test of such a specimen. The model of equivalent material stiffness greatly reduces the complexity of the FE approximation by eliminating the need to define a pouch or an internal pressure field. Therefore, the prediction method could be used in a design tool for pressure-adaptive honeycomb structures.

Effect of Strain Rate on Plastic Flow in Zr-Based Metallic-Glass-Reinforced Porous Tungsten Matrix Composites

The rate-dependent deformation of Zr38Ti17Cu10.5Co12Be22.5 bulk metallic-glass-reinforced porous tungsten matrix composites was investigated over a wide range of strain rates. The composites were examined in two forms: the as-cast composite and the as-extruded composite by extrusion. In addition to showing greater strain hardening, the as-cast composite also shows much more obvious strain rate dependence of flow stress than the as-extruded composite. Microhardness tests were performed on the tungsten and the metallic glass phase in both composites, respectively. The results from the microhardness measurements indicate that the strain rate sensitivity of the as-extruded composite is primarily a result of strain rate sensitivity of the tungsten phase.

Strain response of an instrumented intramedullary nail to three-point bending

Objectives: An experimental biomechanical evaluation of an instrumented intramedullary nail (TriGen® META Nail, Smith&Nephew®) was undertaken. The objectives were two-fold. The first was to identify the most sensitive strain gauge positions and orientations on the nail, and the second was to demonstrate that the nail was capable of detecting changes in stiffness of the nail–bone composite. The function of the instrumented nail is to quantify fracture healing objectively and directly, and so to predict delayed repair or non-union 2 months before current methods.Methods: Eight flat pockets were machined onto the surface of the nail and three strain gauges attached in each pocket. The instrumented nail was inserted into fourth generation biomechanical grade Sawbones® tibiae with three different fracture configurations as well as into a non-fractured bone. The nail–bone composite was loaded in three-point bending at five positions to determine the strain changes in each of the eight strain gauge pockets located along the length of the nail. To simulate callus in the simplest way and to increase the stiffness of the nail–bone composite, loops of duct tape in multiples of four were applied over the fracture locus. A three-point loading jig was used to obtain the change in strain with increasing stiffness. Relative displacement of the bone ends was quantified using radiostereometric analysis.Results: There was no single position of greatest strain sensitivity for all fracture types. The greatest change in strain occurred when the strain gauge pocket and fracture line were closest. Applying the loading moment directly over the strain gauge pocket also maximised its sensitivity. The duct tape callus simulation showed that the instrumented nail was able to detect a change in stiffness of less than 4.1 Nm/°.Conclusions: It has been shown that the instrumented nail can detect physiologically relevant changes in stiffness, and so to provide a useful function as an objective monitor of fracture repair.

One-pot synthesized polyurethane-based nanocomposites filled by original rectorite with enhanced strength and elongation

The unmodified rectorite (REC), a kind of layered silicate, was incorporated into polyurethane (PU) as matrix by the process of one-pot synthesizing polyurethane in situ, and hence produced a series of nanocomposite materials with enhanced strength and elongation. It is worth noting that the nanocomposite containing 2 wt% REC had the maximum elongation (1 449%) and strength (32.66 MPa) as ca. 2.7- and 1.4-fold over those of neat PU film, respectively. Meanwhile, the unexfoliated agglomerates and exfoliated nanoplatelets of REC co-existed in PU matrix. By virtue of strong interfacial interaction on the surface of REC lamella, the stress facilely transferred to the rigid RECs and hence contributed to the enhancement of strength in spite that the original structure and interaction in the PU matrix were partly cleaved. Moreover, the intertwisting of polymer chains in PU matrix with REC as well as the gliding among the REC lamellae might produce greater strain. Nevertheless, excess unexfoliated REC agglomerates under high loading level inhibited the enhancement of mechanical performances, which verified the key role of exfoliated REC nanoplatelet in improving mechanical performances. As a result, this work submitted a simple method to develop a polyurethane-based nanocomposite with high mechanical performances without any modification of layered silicates and the complicated treatment for exfoliation and dispersion.

Alleviating fatigue and failure of NiTi endodontic files by a coating containing inorganic fullerene-like WS2 nanoparticles

Abstract

Modeling stress–strain state of screw transpedicular spine fixation system with variable structure of the vertebral body

To ensure the stability of the spine in the postoperative period transpedicular fixation spine's elements is often used. Usually transpedicular system is formed from the rods that eventually form the frame structure type, attached with screws to the vertebrae. Such design must be rigid and take active part spine loads without significant deformation. Simple transpedicular system can be represented as: bone-1–transpedicular screw-1–Bar–transpedicular screw-2–bell-2–Cage–bell-1. This bar takes in about 20% and Cage takes in about 80% applied load. From the standpoint of improving the well-known structures interest should be given in their stress–strain state as a whole, and for each of the elements, in particular. This study was held in modeling of pedicle screw and the estimation of its deformation, taking into account the interaction with the body of vertebra, which has a variable structure. Vertebra has a complex structure provided with hard enough outer (cortical) layer and soft inner body. A simplified model can be considered with homogeneous materials characterized by different Young's modulus and Poisson's ratio. Transpedicular screw can be represented as a bar having a variable cross-section, located on an elastic base, characterized by different modulus of subgrade reaction. The modulus of subgrade reaction of the elastic foundation is changing stepwise at the transition from one layer of the vertebral body to another. In addition, it is assumed that the vertebra is rigidly clamped (conditionally stationary), and the load is transferred from the screw rod, being uniformly distributed along the length of the local section at the end of the screw. The numerical solution of this problem was obtained by using the generalized Heaviside function. Analysis of the solution indicates that the greatest strain occurs in the area of the screw located in the cortical layer of the vertebra, while the rest is practically not deformed. The same problem was solved by the finite element method in the medium CosmosDesignStar. At the same time 3D-models were used for the spinal segment, fixed transpedicular system. Results of solutions obtained by the two methods described above were sufficiently close, suggesting the adequacy of the proposed model with respect to the real conditions. Thus, the proposed technique can be used to analyze the stress–strain state of various screws, to assess the impact of new constructional elements of screws on the nature of their deformations, to develop improved designs of transpedicular systems, including their dynamics.

Martin Meyerson

Martin Meyerson’s career demonstrates the range and variety of achievement that is possible in the world of planning. Beginning as a practitioner in the Chicago Housing Authority, he went on to become one of the most important planning theorists and academics of the 1950s. However, the major part of his career was devoted to institution building as a university president. At the University of California, Berkeley, during the tumultuous early 1960s, he steered the university through a great crisis but did not receive recognition. At the State University of New York, in the 1970s, he took on the task of a huge expansion, which resulted in great strain and conflict. However, his major achievement was as president of the University of Pennsylvania, which was rejuvenated academically, financially, and physically under his leadership.

Caring for a loved one with cancer

I am a physician who had been diagnosed with throat cancer 4 years ago. I very much appreciate the care and support I received from my family. They endured with me the difficult times I went through, often neglecting their own needs. I personally experienced the great strain and challenges they faced in caring for me. I realized that there is a need to highlight and improve the attention given to caregivers of patients with cancer. Being a caregiver for a loved one with a serious illness such as head and neck cancer is very difficult. It can be extremely hard to watch their loved one suffer especially if there is little that they can do to reverse the illness. It can be physically and emotionally very taxing. Caregivers should, however, realize how important is what they are doing even when they get no or little appreciation. Caregivers often fear the potential death of their loved one and life without them. This can be very anxiety provoking and depressive. Some cope by refusing to accept the diagnosis of cancer and believe that their loved ones’ illness is less serious in nature. Caregivers often sacrifice their own well-being and needs to accommodate those of the person they care for. They often have to calm down their loved one’s fears and support them despite being often the target of their vented anger, frustrations, and anxieties. These frustrations may be exaggerated in those with head and neck cancer who have often difficulties in expressing themselves verbally. Caregivers frequently suppress their own feelings and hide their own emotions so as not to upset the sick person. All of this is very taxing and difficult. It is very useful for the patient and their caregivers to openly and honestly talk to each other, sharing their feelings, worries, and aspiration. This may be more difficult in those who have difficulties in speaking. Jointly meeting the health care providers allows for better communication and facilitates shared decision-making. Unfortunately, the well-being of caregivers is frequently ignored as all the attention is focused on the sick individual. It is essential, however, that the needs of the caregivers are not ignored. Getting physical and emotional support through friends, family, support groups, and mental health professionals can be very helpful for the caregiver. Professional counseling can be an individual or joint one with other family members and or the patient. They should find time for themselves to “recharge” their own batteries. Having time dedicated to their own needs can help them continue to be a source of support and strength for their loved ones. Dr. Brook is the author of the book My voice: a physician’s personal experience with throat cancer. The book can be read at http://dribrook.blogspot.com