43 research outputs found

    Single point incremental forming: An assessment of the progress and technology trends from 2005 to 2015

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    The last decade has seen considerable interest in flexible forming processes. Among the upcoming flexible forming techniques, one that has captured a lot of interest is single point incremental forming (SPIF), where a flat sheet is incrementally deformed into a desired shape by the action of a tool that follows a defined toolpath conforming to the final part geometry. Research on SPIF in the last ten years has focused on defining the limits of this process, understanding the deformation mechanics and material behaviour and extending the process limits using various strategies. This paper captures the developments that have taken place over the last decade in academia and industry to highlight the current state of the art in this field. The use of different hardware platforms, forming mechanics, failure mechanism, estimation of forces, use of toolpath and tooling strategies, development of process planning tools, simulation of the process, aspects of sustainable manufacture and current and future applications are individually tracked to outline the current state of this process and provide a roadmap for future work on this process

    Impact of prevalent and incident vertebral fractures on utility: results from a patient-based and a population-based sample

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    Data are scarce on the impact of vertebral fractures (VFX) on utility. The objective of this study was to assess the impact of prevalent and incident VFX on utility in both a patient-based and population-based sample. Data from the Multiple Outcomes of Raloxifene Evaluation (MORE) study (n = 550 for prevalent VFX and n = 174 for incident VFX) and the European Prospective Osteoporosis Study (EPOS) (n = 236) were used. Utility was assessed by the index score of the EQ-5D. In the MORE study, highly statistically significant associations were found between utility and the presence of prevalent VFX (p < 0.001), number of prevalent VFX (p < 0.001), severity of prevalent VFX (p < 0.001), the combination of number and severity of prevalent VFX (p = 0.001) and location of prevalent VFX (p = 0.019). The mean utility was significantly lower among women who suffered an incident VFX (utility = 0.67) than among women who did not (utility = 0.77) (p = 0.005), although utility loss was not significantly different between the two groups (p = 0.142). In EPOS, the combination of number and severity of incident VFX was significantly related to utility (p = 0.030). In conclusion, utility is lower among persons with prevalent and incident VFX, especially in a patient-based sample. Utility loss was not significantly different between women without and with incident VFX

    Review on the influence of process parameters in incremental sheet forming

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    Incremental sheet forming (ISF) is a relatively new flexible forming process. ISF has excellent adaptability to conventional milling machines and requires minimum use of complex tooling, dies and forming press, which makes the process cost-effective and easy to automate for various applications. In the past two decades, extensive research on ISF has resulted in significant advances being made in fundamental understanding and development of new processing and tooling solutions. However, ISF has yet to be fully implemented to mainstream high-value manufacturing industries due to a number of technical challenges, all of which are directly related to ISF process parameters. This paper aims to provide a detailed review of the current state-of-the-art of ISF processes in terms of its technological capabilities and specific limitations with discussions on the ISF process parameters and their effects on ISF processes. Particular attention is given to the ISF process parameters on the formability, deformation and failure mechanics, springback and accuracy and surface roughness. This leads to a number of recommendations that are considered essential for future research effort

    The prognosis for pain, disability, activities of daily living and quality of life after an acute osteoporotic vertebral body fracture: its relation to fracture level, type of fracture and grade of fracture deformation

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    The level of the acute osteoporotic vertebral fracture, fracture type and grade of fracture deformation were determined in 107 consecutive patients and related to pain, disability, activities of daily living (ADL) and quality of life (QoL) after 3 weeks, 3, 6 and 12 months. Two-thirds of the fractured patients were women and with a similar average age, around 75 years, as the men. Fifty-eight of the acute fractures were located in the thoracic spine and 49 in the lumbar spine and predominantly at the Th12 and L1 levels. Sixty-nine percent of the fractures were wedge, 19% concave and 12% crush fractures. There were 22 mildly, 50 moderately and 35 severely deformed vertebrae. The grade of fracture deformation was not related to gender, age or fracture location. Severely deformed vertebrae predominantly (92%) occurred among the crush fracture type. One year after the fracture, irrespective of fracture level, fracture type or grade of fracture deformation, 4/5 still had pronounced pain and deteriorated QoL. Initial severe fracture deformation by far was the worst prognostic factor for severe lasting pain and disability, and deterioration of ADL and QoL. Factors like fracture level, lumbar fractures tended to improve steadily while thoracic deteriorated, type of fracture, the wedge and concave resulting in less pain and better QoL than the crush fracture type and gender influenced to a lesser extent the outcomes during the year after the acute fracture

    The course of the acute vertebral body fragility fracture: its effect on pain, disability and quality of life during 12 months

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    The vertebral body fracture is the most frequent bone fragility fracture. In spite of this there is considerable uncertainty about the frequency, extent and severity of the acute pain and even more about the duration of pain, the magnitude of disability and how much daily life is disturbed in the post-fracture period. The aim of the present study was to follow the course of pain, disability, ADL and QoL in patients during the year after an acute low energy vertebral body fracture. The study design was a longitudinal cohort study with prospective data collection. All the patients over 40 years admitted to the emergency unit because of back pain with a radiologically acute vertebral body fracture were eligible. A total of 107 patients were followed for a year. The pain, disability (von Korff pain and disability scores), ADL (Hannover ADL score), and QoL (EQ-5D) were measured after 3 weeks, 3, 6 and 12 months. Two-thirds of the patients were women, and were similar in average age, as the men around 75 years. A total of 65.4% of the fractures were due to a level fall or a minor trauma, whereas 34.6% had no recollection of trauma or a specific event as the cause of the fracture. A total of 76.6% of the fractured patients were immediately mobilized and allowed to return home while the remaining were hospitalized. The average pain intensity score after 3 weeks was 70.9 (SD 19.3), the disability score 68.9 (SD 23.6), the ADL score 37.7 (SD 22.1) and EQ-5D score of 0.37 (SD 0.37). The largest improvements, 10–15%, occurred between the initial visit and the 3 months follow-up and were quite similar for all the measures. From 3 months, all the outcome measures leveled out or tended to deteriorate resulting in a mean pain intensity score of 60.5, disability score of 53.9, ADL score of 47.6, and EQ-5D score 0.52 after 12 months. After a whole year the fractured patients’ condition was similar to the preoperative condition of patients with a herniated lumbar disc, central lumbar spinal stenosis or in patients 100% work disabled due to back or neck problems. Instead of the generally believed good prognosis for the greater majority of those fractured, the acute vertebral body fracture was the beginning of a long-lasting severe deterioration of their health

    Health-related quality of life after vertebral or hip fracture: a seven-year follow-up study

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    <p>Abstract</p> <p>Background</p> <p>The negative impact of vertebral and hip low-energy fractures on health-related quality-of-life (HRQOL) has been demonstrated previously, but few prospective long-term follow-up studies have been conducted. This study aims to (i) investigate the changes and long-term impact of vertebral or hip fracture and between fracture groups on HRQOL in postmenopausal women prospectively between two and seven years after the inclusion fracture, (ii) compare HRQOL results between fracture and reference groups and (iii) study the relationship between HRQOL and physical performance, spinal deformity index and bone mineral density at seven-year follow-up.</p> <p>Methods</p> <p>Ninety-one women examined two years after a low-energy vertebral or hip fracture were invited to a new examination seven years after the diagnosis. HRQOL was examined using the SF-36 questionnaire and was compared with an age and sex-matched reference group. Physical function was assessed using tests and questionnaires. Bone mineral density was measured. Radiographs of the spine were evaluated using the visual semiquantitative technique. A longitudinal and cross-sectional design was used in this study. Statistical analyses included descriptive statistics, Student's <it>t</it>-tests, ANCOVA, and partial correlation.</p> <p>Results</p> <p>Sixty-seven women participated. In the 42 women (mean age 75.8, SD 4.7) with vertebral fracture as inclusion fracture, bodily pain had deteriorated between two and seven years and might be explained by new fracture. Remaining pronounced reduction of HRQOL was seen in all domains except general health and mental health at seven-year follow-up in women with vertebral fractures compared to the reference group (p < 0.05). All 25 women (mean age 75.0, SD 4.7) with hip fracture as inclusion fracture had no significant changes in HRQOL between two and seven years and did not differ from the reference group regarding HRQOL after seven years. The vertebral group had significantly lower values for bodily pain, vitality, role-emotional function and mental health compared to the hip group. HRQOL showed a positive relationship between physical activity, static balance and handgrip strength.</p> <p>Conclusion</p> <p>The long-term reduction of HRQOL in women with vertebral fracture emerged clearly in this study. The relationships between HRQOL and physical performance in women with vertebral and hip fracture raise questions for more research.</p

    Investigation of the effect of forming parameters in incremental sheet forming using a micromechanics based damage model

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    The incremental sheet forming (ISF) process is considered as a feasible solution for forming a variety of small batch and even customised sheet components. The quality of an ISF product is affected by various process parameters, e.g. sheet material, step-down, feed rate, tool diameter and lubricant. To produce an ISF part of sufficient quality and accuracy without defects, optimal parameters of the ISF process should be selected. In the present work, experiments and FE analyses were conducted to evaluate the influence of the main ISF process parameters including the step-down, feed rate and tool diameter on the formability and fracture of two types of pure Ti (grade 1 and 2). The Gurson–Tvergaard-Needleman (GTN) damage constitutive model with consideration of stress triaxiality was developed to predict ductile fracture in the ISF process due to void nucleation, growth and coalescence. It was found that the ISF parameters have varying degrees of effect on the formability and fracture occurrence of the two types of pure Ti, and grade 2 pure Ti sheet is more sensitive than grade 1 Ti sheet to the forming parameters due to low ductility

    The effect of osteoporotic vertebral fracture on predicted spinal loads in vivo

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    The aetiology of osteoporotic vertebral fractures is multi-factorial, and cannot be explained solely by low bone mass. After sustaining an initial vertebral fracture, the risk of subsequent fracture increases greatly. Examination of physiologic loads imposed on vertebral bodies may help to explain a mechanism underlying this fracture cascade. This study tested the hypothesis that model-derived segmental vertebral loading is greater in individuals who have sustained an osteoporotic vertebral fracture compared to those with osteoporosis and no history of fracture. Flexion moments, and compression and shear loads were calculated from T2 to L5 in 12 participants with fractures (66.4 ± 6.4 years, 162.2 ± 5.1 cm, 69.1 ± 11.2 kg) and 19 without fractures (62.9 ± 7.9 years, 158.3 ± 4.4 cm, 59.3 ± 8.9 kg) while standing. Static analysis was used to solve gravitational loads while muscle-derived forces were calculated using a detailed trunk muscle model driven by optimization with a cost function set to minimise muscle fatigue. Least squares regression was used to derive polynomial functions to describe normalised load profiles. Regression co-efficients were compared between groups to examine differences in loading profiles. Loading at the fractured level, and at one level above and below, were also compared between groups. The fracture group had significantly greater normalised compression (p = 0.0008) and shear force (p < 0.0001) profiles and a trend for a greater flexion moment profile. At the level of fracture, a significantly greater flexion moment (p = 0.001) and shear force (p < 0.001) was observed in the fracture group. A greater flexion moment (p = 0.003) and compression force (p = 0.007) one level below the fracture, and a greater flexion moment (p = 0.002) and shear force (p = 0.002) one level above the fracture was observed in the fracture group. The differences observed in multi-level spinal loading between the groups may explain a mechanism for increased risk of subsequent vertebral fractures. Interventions aimed at restoring vertebral morphology or reduce thoracic curvature may assist in normalising spine load profiles. © 2006 Springer-Verlag
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