Large Deformation Finite Element Analyses for 3D X-ray CT Scanned Microscopic Structures of Polyurethane Foams

Polyurethane foams have unique properties that make them suitable for a wide range of applications, including cushioning and seat pads. The foam mechanical properties largely depend on both the parent material and foam cell microstructure. Uniaxial loading experiments, X-ray tomography and finite element analysis can be used to investigate the relationship between the macroscopic mechanical properties and microscopic foam structure. Polyurethane foam specimens were scanned using X-ray computed tomography. The scanned geometries were converted to three-dimensional (3D) CAD models using open source, and commercially available CAD software tools. The models were meshed and used to simulate the compression tests using the implicit finite element method. The calculated uniaxial compression tests were in good agreement with experimental results for strains up to 30%. The presented method would be effective in investigating the effect of polymer foam geometrical features in macroscopic mechanical properties, and guide manufacturing methods for specific applications.

Introduction to the special issue on comfort: A review of 26 papers from the International Comfort Congress 2019

Various aspects related to comfort are described in this special issue. Some papers are focused on the environment, like smell, temperature, light, acoustics, space and some on an artefact touching the human, like the floor angle, the seat, a bed and light. However, in this special issue also topics like modelling and behavior get more attention.

PCQ: Preferred Comfort Questionnaires for product design

BACKGROUND:

Selecting the most suitable questionnaire(s) in comfort research for product design is always a challenge, even for experienced researchers.

OBJECTIVE:

The objective of this research is to create a list of Preferred Comfort Questionnaires (PCQ) for product design to help researchers in the selection of questionnaires for comfort research.

METHODS:

Fifteen questionnaires that are often used in comfort research for product design were selected as candidate questionnaires. During the Second International Comfort Congress (ICC 2019), 55 researchers and practitioners working in the field of comfort joined together in a workshop to rate these questionnaires individually as well as rank them in groups based on their experience. The criteria of rating and ranking included easiness to answer, easiness for data interpretation, time needed to complete, the need for prior training, as well as mapping the applicable design phases and field of application.

RESULTS:

The elicited responses related to each questionnaire were analyzed. For comfort research in five proposed application fields and four design phases, the preferred questionnaires were highlighted and categorized into four categories: preferred questionnaire, suitable for less prior training, suitable for fast completion and generally applicable, which led to a list of PCQ for product design.

CONCLUSION:

We expect that the PCQ list can be used as a useful instrument to help researchers in selecting questionnaires for comfort research in product design.

Integrating and applying models of comfort

This paper gives an overview of the relevance of the comfort concept, its definitions, boundary conditions, and stakeholders. Current comfort theories are presented and reflected on, both in their applicability and testing methodology. Questionnaires commonly used to study comfort and discomfort are also reviewed. An example of a comfort lab is introduced in its functionality and tools, which can be useful as a benchmark for others studying comfort.

Engineering movement into automotive seating: Does the driver feel more comfortable and refreshed?

The concept of introducing movement in automotive seating was investigated. Three seat conditions, a control (no movement) and two movement conditions (fore-aft and cushion-backrest) were compared. Movement was introduced at a fixed speed, slow, smooth and within a small range. Ten participants took part in a 60 min simulated drive for each condition - single blind, repeated measures, and balanced order. Discomfort ratings were collected for six body areas and overall discomfort, together with a wellbeing questionnaire. Driver posture and Seat Fidgets and Movements (SFMs) were captured. There was a trend for lower ratings of discomfort, overall and in the neck, shoulders, lower back, buttocks, and ankles with both seat movement conditions. Wellbeing ratings were also better with movement. Significant differences were found at minute 60 for buttock discomfort - less discomfort with seat movement. Overall discomfort and SFMs frequency increased with time driving. Generally, passive seat movement was well received.

Neonatal head and torso vibration exposure during inter-hospital transfer

Inter-hospital transport of premature infants is increasingly common, given the centralisation of neonatal intensive care. However, it is known to be associated with anomalously increased morbidity, most notably brain injury, and with increased mortality from multifactorial causes. Surprisingly, there have been relatively few previous studies investigating the levels of mechanical shock and vibration hazard present during this vehicular transport pathway. Using a custom inertial datalogger, and analysis software, we quantify vibration and linear head acceleration. Mounting multiple inertial sensing units on the forehead and torso of neonatal patients and a preterm manikin, and on the chassis of transport incubators over the duration of inter-site transfers, we find that the resonant frequency of the mattress and harness system currently used to secure neonates inside incubators is [Formula: see text]. This couples to vehicle chassis vibration, increasing vibration exposure to the neonate. The vibration exposure per journey (A(8) using the ISO 2631 standard) was at least 20% of the action point value of current European Union regulations over all 12 neonatal transports studied, reaching 70% in two cases. Direct injury risk from linear head acceleration (HIC15) was negligible. Although the overall hazard was similar, vibration isolation differed substantially between sponge and air mattresses, with a manikin. Using a Global Positioning System datalogger alongside inertial sensors, vibration increased with vehicle speed only above 60 km/h. These preliminary findings suggest there is scope to engineer better systems for transferring sick infants, thus potentially improving their outcomes.

Driver discomfort in vehicle seats - Effect of changing road conditions and seat foam composition

Discomfort in vehicle seats is a multi-factorial problem with contributions occurring from effects of sitting duration, seat design, and the dynamic environment to which the occupant is exposed. This paper reports laboratory studies investigating the extent to which reports of discomfort are affected by vibration commencing or ceasing, and whether methods of assessment are sensitive enough to detect small changes in foam composition. Study 1 measured discomfort ratings for two conditions of 60 min each, comprising 30 min of vibration exposure followed by 30 min of static sitting in a car seat, and vice-versa. Study 2 measured discomfort ratings for three conditions over a period of 40 min each, whilst participants were sitting in one of two car seat compositions, and either exposed to vibration or not. In both studies participants operated a driving simulator. It is shown that exposure to vibration increases the rate of discomfort onset in comparison to periods of static sitting. When vibration stopped, there was an acute improvement in comfort but discomfort did not drop to the levels reported by those who had been unexposed. When vibration started after 30 min of static sitting, there was an acute increase in discomfort but not to the levels reported by those who had been exposed to 30 min of vibration. After 40 min of continuous exposure it was possible to detect significant differences in overall discomfort between the two seat compositions, although trends could be observed in less time.

Driving performance and driver discomfort in an elevated and standard driving position during a driving simulation

The primary purposes of a vehicle driver's seat, is to allow them to complete the driving task comfortably and safely. Within each class of vehicle (e.g. passenger, commercial, industrial, agricultural), there is an expected driving position to which a vehicle cabin is designed. This paper reports a study that compares two driving positions, in relation to Light Commercial Vehicles (LCVs), in terms of driver performance and driver discomfort. In the 'elevated' driving position, the seat is higher than usually used in road vehicles; this is compared to a standard driving position replicating the layout for a commercially available vehicle. It is shown that for a sample of 12 drivers, the elevated position did not, in general, show more discomfort than the standard position over a 60 min driving simulation, although discomfort increased with duration. There were no adverse effects shown for emergency stop reaction time or for driver headway for the elevated posture compared to the standard posture. The only body part that showed greater discomfort for the elevated posture compared to the standard posture was the right ankle. A second experiment confirmed that for 12 subjects, a higher pedal stiffness eliminated the ankle discomfort problem.

Prenatal diagnosis using combined quantitative fluorescent polymerase chain reaction and array comparative genomic hybridization analysis as a first-line test: results from over 1000 consecutive cases

OBJECTIVES

First, to assess the performance of a prenatal diagnostic service using quantitative fluorescent polymerase chain reaction (QF-PCR) and array comparative genomic hybridization (aCGH) as first-line investigations. Second, to determine the incidence of copy number variants (CNVs) by indication for testing, with particular reference to ultrasound and biochemical parameters measured in combined first-trimester screening.

METHODS

All patients undergoing invasive prenatal testing at a specialist prenatal screening service in Sydney, Australia, were included in the study. All samples underwent QF-PCR and targeted aCGH.

RESULTS

Of 1049 cases, CNVs were reported in 156 (14.9%). Preliminary QF-PCR identified abnormalities in 104 of these cases. Of the remaining 52 cases, 20 could have been detected on karyotype testing, leaving 32 cases (3.1%) with CNVs only detectable by aCGH, of which 13 (1.2%) were pathogenic. Variants of unknown significance (VOUS) were seen in only three cases. Fetal structural abnormalities identified in the first trimester were the group most likely to be associated with pathogenic CNVs (11.8%).

CONCLUSIONS

Combining QF-PCR and aCGH is an effective first-tier prenatal testing regime that does not require conventional karyotyping. The incidence of VOUS in this study was very low owing to appropriate aCGH targeting and specific reporting criteria that reduced the number of potentially difficult counseling encounters. Pathogenic CNVs are positively correlated with the presence of fetal structural abnormalities, but not with enlarged nuchal translucency or abnormal first-trimester serology results.

Bilateral ground reaction forces and joint moments for lateral sidestepping and crossover stepping tasks

Racquet sports have high levels of joint injuries suggesting the joint loads during play may be excessive. Sports such as badminton employ lateral sidestepping (SS) and crossover stepping (XS) movements which so far have not been described in terms of biomechanics. This study examined bilateral ground reaction forces and three dimensional joint kinetics for both these gaits in order to determine the demands of the movements on the leading and trailing limb and predict the contribution of these movements to the occurrence of overuse injury of the lower limbs. A force platform and motion-analysis system were used to record ground reaction forces and track marker trajectories of 9 experienced male badminton players performing lateral SS, XS and forward running tasks at a controlled speed of 3 m·s(-1) using their normal technique. Ground reaction force and kinetic data for the hip, knee and ankle were analyzed, averaged across the group and the biomechanical variables compared. In all cases the ground reaction forces and joint moments were less than those experienced during moderate running suggesting that in normal play SS and XS gaits do not lead to high forces that could contribute to increased injury risk. Ground reaction forces during SS and XS do not appear to contribute to the development of overuse injury. The distinct roles of the leading and trailing limb, acting as a generator of vertical force and shock absorber respectively, during the SS and XS may however contribute to the development of muscular imbalances which may ultimately contribute to the development of overuse injury. However it is still possible that faulty use of these gaits might lead to high loads and this should be the subject of future work. Key pointsGround reaction forces and joint moments during lateral stepping are smaller in magnitude than those experienced during moderate running.Force exposure in SS and XS gaits in normal play does not appear to contribute to the development of overuse injuryThe leading and trailing limbs perform distinct roles, acting as a generator of vertical force and shock absorber respectively.This distinct contribution may contribute to the development of muscular imbalances which may ultimately contribute to the development of overuse injury.