An equation for bolt clampup relaxation in transient environments

An equation for bolt clampup relaxation for transient temperature-moisture (T-M) conditions was derived starting with a relaxation equation for steady-state conditions, and then using an incremental time approach that exploits the superposition principle for linear viscoelasticity. The resulting equation uses the initial T-M condition (at the time of clamping), the T-M history after clamping, and elastic clampup coefficients for temperature and moisture changes. For a given material and joint configuration, the clampup coefficients are constants that can be calculated by elastic analyses. The clampup equation was used to calculate the changes in clampup occurring in a T300/5208 graphite/epoxy joint exposed to a one-year history of temperature and moisture. Two cases were considered: one was a dry joint exposed to a relatively humid environment and the other was a nearly saturated joint exposed to an arid environment

Bolt clampup relaxation in a graphite/epoxy laminate

A simple bolted joint was analyzed to calculate bolt clampup relaxation for a graphite/epoxy (T300/5208) laminate. A viscoelastic finite element analysis of a double-lap joint with a steel bolt was conducted. Clampup forces were calculated for various steady-state temperature-moisture conditions using a 20-year exposure duration. The finite element analysis predicted that clampup forces relax even for the room-temperature-dry condition. The relaxations were 8, 13, 20, and 30 percent for exposure durations of 1 day, 1 month, 1 year, and 20 years, respectively. As expected, higher temperatures and moisture levels each increased the relaxation rate. The combined viscoelastic effects of steady-state temperature and moisture appeared to be additive. From the finite-element analysis, a simple equation was developed for clampup force relaxation. This generalized equation was used to calculate clampup forces for the same temperature-moisture conditions as used in the finite-element analysis. The two sets of calculated results agreed well

Effects of T-tabs and large deflections in DCB specimen tests

A simple strength of materials analysis was developed for a double-cantilever beam (DCB) specimen to account for geometric nonlinearity effects due to large deflections and T-tabs. A new DCB data analysis procedure was developed to include the effects of these nonlinearities. The results of the analysis were evaluated by DCB tests performed for materials having a wide range of toughnesses. The materials used in the present study were T300/5208, IM7/8551-7, and AS4/PEEK. Based on the present analysis, for a typical deflection/crack length ratio of 0.3 (for AS4/PEEK), T-tabs and large deflections cause a 15 percent and 3 percent error, respectively, in the computer Mode 1 strain energy release rate. Design guidelines for DCB specimen thickness and T-tab height were also developed in order to keep errors due to these nonlinearities within 2 percent. Based on the test results, for both hinged and tabbed specimens, the effects of large deflection on the Mode 1 fracture toughness (G sub Ic) were almost negligible (less than 1 percent) in the case of T300/5208 and IM7/8551-7; however, AS4/PEEK showed a 2 to 3 percent effect. The effects of T-tabs G sub Ic were more significant for all the materials with T300/5208 showing a 5 percent error, IM7/8551-7 a 15 percent error, and, AS4/PEEK a 20 percent error

Usability Inspection Report of iLumina

iLumina is a digital library of sharable undergraduate teaching resource materials for science, mathematics, technology, and engineering being developed by the University of North Carolina at Wilmington (UNCW), Collegis, Virginia Tech, Georgia State University, Grand Valley State and The College of New Jersey. Types of iLumina resources include papers, tutorials, applets, presentations, visualizations, experiments, assignments, software, exercises

A Methodology for Characterization of the Strain Rate-Dependent Behavior of PU Foam

Polymeric foams are known to be sensitive to strain rate under dynamic loads. Mechanical characterization of such materials would not thus be complete without capturing the effect of strain rate on their stress-strain behaviors. Consistent data on the dynamic behavior of foam is also necessary for designing energy-absorbing countermeasures based on foam such as for vehicle occupant safety protection. Strain rates of the order of 100-500 s−1 are quite common in such design applications; strain rates of this range cannot be obtained with an ordinary UTM (universal testing machine) and a special test set-up is usually needed. In the current study, a unique approach has been suggested according to which quasi-static tests at low strain rates and low velocity drop tests at medium strain rates are utilized to arrive at an empirical relation between initial peak stress and logarithm of strain rate for a rigid closed-cell PU foam. Using a stress-scaling methodology and the empirical relation mentioned, foam stress-strain curves are obtained for a number of strain rates spanning low (from 0.00033 s−1) to high strain rates (up to1000 s−1). This data on foam material behavior is expected to be particularly useful in numerical modelling of foam-based countermeasures for impact energy absorption applications

Evolving Neural Networks Applied to Predator-Evader Problem

The creation of strategies to meet abstract goals is an important behavior exhibited by natural organisms. A situation requiring the development of such strategies is the predator-evader problem. To study this problem, Khepera robots are chosen as the competing agents. Using computer simulations the evolution of the adaptive behavior is studied in a predator-evader interaction. A bilaterally symmetrical multilayer perceptron neural network architecture with evolvable weights is used to model the “brains” of the agents. Evolutionary programming is employed to evolve the predator for developing adaptive strategies to meet its goals. To study the effect of learning on evolution a self-organizing map (SOM) is added to the architecture, it is trained continuously and all the predators can access its weights. The results of these two different approaches are compared

Giant cell tumor of flexor tendon sheath of little finger: a case report

Giant cell tumor of the tendon sheath is a benign proliferative lesion of synovial origin that may affect the joints, bursae and tendon sheaths. We report the case of a giant cell tumor of the tendon sheath arising from the flexor tendon sheath of 5th finger of left hand of a 44 year old male patient. The patient underwent ultrasound examination and subsequently magnetic resonance imaging

Surgical management of fractures of distal end radius using uniplanar external fixator augmented with percutaneous kirschner wire fixation

Background: Distal end radius fractures is one of the most common fractures of the upper limb especially in the elderly population, accounting for about 17% of all upper limb fractures. Surgical stabilization of these fractures remains a challenge even today. Although the recent trend is towards internal fixation with locking plates, the external fixator itself has its own advantages in the treatment of these fractures.Methods: This study is a prospective, time bound, hospital based study conducted in Kempegowda Institute of Medical Sciences and Research Center, Bangalore, between November 2014 to April 2016. The study included 30 cases of distal end radius fractures that were operated with the closed reduction and uniplanar external fixator augmented with k-wire for distal end radius by the principle of ligamentotaxis.Results: In our study, 14 (46.6 %) patients had excellent results. Whereas, 11 (36.7%) patients had good results and 3 (10%) had fair and only 2 (6.7%) patients had poor results. Most of the fractures united by 12 weeks. Complications associated with the study was stiffness, malunion, sudeck’s  osteodystrophy and pin tract infection. Conclusions: The uniplanar external fixator augmented with k-wire is a good choice in the treatment of distal end radius fractures  in terms of providing a good functional outcome if proper preoperative planning, good reduction and surgical technique are followed, leading to high rate of bone union, minimal soft tissue damage and complications

Perinatal Symptoms and Treatment Engagement in Female Veterans

INTRODUCTION: Women veterans using Veterans Health Care Administration maternity benefits have a high prevalence of mental health disorders, including depression, PTSD, and anxiety. Additionally, women with psychiatric histories often experience a relapse or worsening of symptoms during pregnancy and postpartum. Adequate perinatal mental healthcare engagement is critical to optimizing outcomes for mother and child. MATERIALS AND METHODS: This study evaluated psychiatric symptom severity and predictors of women veteran\u27s mental health treatment engagement during pregnancy and postpartum at the VA North Texas Health Care System. Seventy women using Veterans Health Administration were assessed longitudinally via chart review and interviews (including the Edinburgh Postnatal Depression Scale) during pregnancy and postpartum. A Friedman test was used to evaluate the change in symptom severity during (1) the 6 months before pregnancy, (2) pregnancy, and (3) postpartum. Multivariate logistic regressions were used to determine predictors of attending outpatient mental health appointments. Potential predictors examined included sociodemographic factors, symptoms of depression, history of military sexual assault, presence of a pre-pregnancy psychiatric diagnosis, and attendance of mental health appointments before pregnancy. RESULTS: Approximately 40% of participants demonstrated at least mild psychiatric symptoms before pregnancy, and symptom severity did not significantly change across the perinatal period (pre-pregnancy, pregnancy, and postpartum) X2 (2, n = 70) = 3.56, P = .17. Depressive symptoms during the 2nd or 3rd trimester were a significant predictor for attendance of mental health appointments during both pregnancy (OR = 1.18, 95% CI, 1.04 to 1.34) and postpartum (OR = 1.18, 95% CI, 1.02 to 1.36). An active psychiatric diagnosis during the 6 months before pregnancy was also a significant predictor of attendance following delivery (OR = 14.63, 95% CI, 1.55 to 138.51). CONCLUSION: Our results demonstrate that women with prior histories of mental health conditions will continue to be symptomatic, and this is a good predictor of mental health treatment engagement during the perinatal period. This work is written by (a) US Government employee(s) and is in the public domain in the US

Polymer Coated Polymeric (PCP) microneedles for sampling of drugs and biomarkers from tissues

The Polymer Coated Polymeric (PCP) microneedles were fabricated using PVP K30 in the core and ethyl cellulose in the coating. The PCP microneedles do not disintegrate in the tissue upon insertion and rather stays intact and allows diffusion of drugs and analytes across the membrane both inward and outward. In this project the potential use of PCP microneedles for sampling analytes from the dermal tissue was explored. The amount of analyte sampled depended on the concentration in the tissue, physicochemical properties of the analyte and duration of insertion of the array in the tissue. Further, an advanced type of PCP microneedle array was fabricated by entrapping absorbent beads in the core microneedles. The adsorbent enabled the PCP microneedles to recover significantly higher amount of analyte from the tissue