Implementation of a non-orthogonal model for the finite element simulation of textile composite draping

In the pursuit of producing high quality, low-cost composite aircraft structures, out-of-autoclave manufacturing processes for textile reinforcements are being simulated with increasing accuracy. This paper focuses on the continuum-based, finite element modelling of textile composites as they deform during the draping process. A non-orthogonal constitutive model tracks yarn orientations within a material subroutine developed for Abaqus/Explicit, resulting in the realistic determination of fabric shearing and material draw-in. Supplementary material characterisation was experimentally performed in order to define the tensile and non-linear shear behaviour accurately. The validity of the finite element model has been studied through comparison with similar research in the field and the experimental lay-up of carbon fibre textile reinforcement over a tool with double curvature geometry, showing good agreement.

A low-cost digital image correlation technique for characterising the shear deformation of fabrics for draping studies

A novel digital image correlation (DIC) technique has been developed to track changes in textile yarn orientations during shear characterisation experiments, requiring only low-cost digital imaging equipment. Fabric shear angles and effective yarn strains are calculated and visualised using this new DIC technique for bias extension testing of an aerospace grade, carbon-fibre reinforcement material with a plain weave architecture. The DIC results are validated by direct measurement, and the use of a wide bias extension sample is evaluated against a more commonly used narrow sample. Wide samples exhibit a shear angle range 25% greater than narrow samples and peak loads which are 10 times higher. This is primarily due to excessive yarn slippage in the narrow samples; hence, the wide sample configuration is recommended for characterisation of shear properties which are required for accurate modelling of textile draping.

Novel system for distant assessment of cataract surgical quality in rural China

BACKGROUND: This study aims to assess the quality of various steps of manual small incision cataract surgery and predictors of quality, using video recordings.
DESIGN: This paper applies a retrospective study.
PARTICIPANTS: Fifty-two trainees participated in a hands-on small incision cataract surgery training programme at rural Chinese hospitals.
METHODS: Trainees provided one video each recorded by a tripod-mounted digital recorder after completing a one-week theoretical course and hands-on training monitored by expert trainers. Videos were graded by two different experts, using a 4-point scale developed by the International Council of Ophthalmology for each of 12 surgical steps and six global factors. Grades ranged from 2 (worst) to 5 (best), with a score of 0 if the step was performed by trainers.
MAIN OUTCOME MEASURES: Mean score for the performance of each cataract surgical step rated by trainers.
RESULTS: Videos and data were available for 49/52 trainees (94.2%, median age 38 years, 16.3% women and 77.5% completing > 50 training cases). The majority (53.1%, 26/49) had performed ≤ 50 cataract surgeries prior to training. Kappa was 0.57∼0.98 for the steps (mean 0.85). Poorest-rated steps were draping the surgical field (mean ± standard deviation = 3.27 ± 0.78), hydro-dissection (3.88 ± 1.22) and wound closure (3.92 ± 1.03), and top-rated steps were insertion of viscoelastic (4.96 ± 0.20) and anterior chamber entry (4.69 ± 0.74). In linear regression models, higher total score was associated with younger age (P = 0.015) and having performed >50 independent manual small incision cases (P = 0.039).
CONCLUSIONS: More training should be given to preoperative draping, which is poorly performed and crucial in preventing infection. Surgical experience improves ratings.© 2015 Royal Australian and New Zealand College of Ophthalmologists.

Perceived difficulty of various steps of manual small incision cataract surgery among trainees in rural China

Background: The perceived difficulty of steps of manual small incision cataract surgery among trainees in rural China was assessed. Design: Cohort study. Participants: Fifty-two trainees at the end of a manual small incision cataract surgery training programme. Methods: Participants rated the difficulty of 14 surgical steps using a 5-point scale, 1 (very easy) to 5 (very difficult). Demographic and professional information was recorded for trainees. Main Outcome Measure: Mean ratings for surgical steps. Results: Questionnaires were completed by 49 trainees (94.2%, median age 38 years, 8 [16.3%] women). Twenty six (53.1%) had performed ≤50 independent cataract surgeries prior to training. Trainees rated cortical aspiration (mean score±standard deviation=3.10±1.14) the most difficult step, followed by wound construction (2.76±1.08), nuclear prolapse into the anterior chamber (2.74±1.23) and lens delivery (2.51±1.08). Draping the surgical field (1.06±0.242), anaesthetic block administration (1.14±0.354) and thermal coagulation (1.18±0.441) were rated easiest. In regression models, the score for cortical aspiration was significantly inversely associated with performing >50 independent manual small incision cataract surgery surgeries during training (P=0.01), but not with age, gender, years of experience in an eye department or total number of cataract surgeries performed prior to training. Conclusions: Cortical aspiration, wound construction and nuclear prolapse pose the greatest challenge for trainees learning manual small incision cataract surgery, and should receive emphasis during training. Number of cases performed is the strongest predictor of perceived difficulty of key steps. © 2013 Royal Australian and New Zealand College of Ophthalmologists.