Toh Yen Pang

Bicycle Helmet Size, Adjustment, and Stability

Objectives: One of the main requirements of a protective bicycle helmet is to provide and maintain adequate coverage to the head. A poorly fitting or fastened helmet may be displaced during normal use or even ejected during a crash. The aims of the current study were to identify factors that influence the size of helmet worn, identify factors that influence helmet position and adjustment, and examine the effects of helmet size worn and adjustment on helmet stability. Methods: Recreational and commuter cyclists in Sydney were surveyed to determine how helmet size and/or adjustment affected helmet stability in the real world. Anthropometric characteristics of the head were measured and, to assess helmet stability, a test analogous to the requirements of the Australian bicycle helmet standard was undertaken. Results: Two hundred sixty-seven cyclists were recruited across all age groups and 91% wore an AS/NZS 2063–compliant helmet. The main ethnic group was Europeans (71%) followed by Asians (18%). The circumferences of the cyclists’ heads matched well the circumference of the relevant ISO headform for the chosen helmet size, but the head shapes differed with respect to ISO headforms. Age and gender were associated with wearing an incorrectly sized helmet and helmet adjustment. Older males (>55 years) were most likely to wear an incorrectly sized helmet. Adult males in the 35–54 year age group were most likely to wear a correctly adjusted helmet. Using quasistatic helmet stability tests, it was found that the correctness of adjustment, rather than size, head dimensions, or shape, significantly affected helmet stability in all test directions. Conclusions: Bicycle helmets worn by recreational and commuter cyclists are often the wrong size and are often worn and adjusted incorrectly, especially in children and young people. Cyclists need to be encouraged to adjust their helmets correctly. Current headforms used in standards testing may not be representative of cyclists’ head shapes. This may create challenges to helmet suppliers if on one hand they optimize the helmet to meet tests on ISO-related headforms while on the other seeking to offer greater range of sizes.

Evaluation of thermal and evaporative resistances in cricket helmets using a sweating manikin.

The main objective of this study is to establish an approach for measuring the dry and evaporative heat dissipation cricket helmets. A range of cricket helmets has been tested using a sweating manikin within a controlled climatic chamber. The thermal manikin experiments were conducted in two stages, namely the (i) dry test and (ii) wet test. The ambient air temperature for the dry tests was controlled to ~ 23 °C, and the mean skin temperatures averaged ~ 35 °C. The thermal insulation value measured for the manikin with helmet ensemble ranged from 1.0 to 1.2 clo. The results showed that among the five cricket helmets, the Masuri helmet offered slightly more thermal insulation while the Elite helmet offered the least. However, under the dry laboratory conditions and with minimal air movement (air velocity = 0.08 ± 0.01 ms(-1)), small differences exist between the thermal resistance values for the tested helmets. The wet tests were conducted in an isothermal condition, with an ambient and skin mean temperatures averaged ~ 35 °C, the evaporative resistance, Ret, varied between 36 and 60 m(2) Pa W(-1). These large variations in evaporative heat dissipation values are due to the presence of a thick layer of comfort lining in certain helmet designs. This finding suggests that the type and design of padding may influence the rate of evaporative heat dissipation from the head and face; hence the type of material and thickness of the padding is critical for the effectiveness of evaporative heat loss and comfort of the wearer. Issues for further investigations in field trials are discussed.

Factors affecting motorcycle helmet use: size selection, stability, and position

Objectives: One of the main requirements of a protective helmet is to provide and maintain appropriate and adequate coverage to the head. A helmet that is poorly fitted or fastened may become displaced during normal use or even ejected during a crash. Methods: Observations and measurements of head dimensions, helmet position, adjustment, and stability were made on 216 motorcyclists. Helmet details were recorded. Participants completed a questionnaire on helmet usability and their riding history. Helmet stability was assessed quasistatically. Results: Differences between the dimensions of ISO headforms and equivalent sized motorcyclists’ heads were observed, especially head width. Almost all (94%) of the helmets were labeled to be compliant with AS/NZS 1698 (2006). The majority of riders were satisfied with the comfort, fit, and usability aspects of their helmets. The majority of helmets were deemed to have been worn correctly. Using quasistatic pull tests, it was found that helmet type (open-face or full-face) and the wearing correctness were among factors that affected the loads at which helmets became displaced. The forces required to displace the helmet were low, around 25 N. Conclusions: The size of the in-use motorcycle helmets did not correspond well to the predicted size based on head dimensions, although motorcyclists were generally satisfied with comfort and fit. The in vivo stability tests appear to overpredict that helmets will come off in a crash, based on the measured forces, tangential forces measured in the oblique impact tests, and the actual rate of helmet ejection.

The Helmet Fit Index - A Method for the Computational Analysis of Fit between Human Head Shapes and Bicycle Helmets

While a bicycle helmet protects the wearers head in the event of a crash, not every user benefits to the same extent when wearing the headgear. A proper fit with the cyclists head is found to be one of the most important attributes to improve protection during impact. A correct fit is defined as a small and uniform distance between the helmet liner and the wearers head shape, with a broad coverage of the head area. The scientific community has recognised the need for improved fitting, but in-depth methods to analyse and compare the fit performance of distinct helmets models are still absent from the literature. We present a method based on 3D anthropometry, reverse engineering techniques and computational analysis to redress this shortcoming. As a result of this study, we introduce the Helmet Fit Index (HFI) as a tool for fit analysis between a helmet model and a human head. It is envisaged that the HFI can provide detailed understanding of helmet efficiency regarding fit and should be used during helmet development phases and testing.

A novel hierarchical clustering algorithm for the analysis of 3D anthropometric data of the human head

ABSTRACTIn recent years, the use of 3D anthropometry for product design has become more appealing because of advances in mesh parameterisation, multivariate analyses and clustering algorithms. The purpose of this study was to introduce a new method for the clustering of 3D head scans. A novel hierarchical algorithm was developed, in which a squared Euclidean metric was used to assess the head shape similarity of participants. A linkage criterion based on the centroid distance was implemented, while clusters were created one after another in an enhanced manner. As a result, 95.0% of the studied sample was classified inside one of the four computed clusters. Compared to conventional hierarchical techniques, our method could classify a higher ratio of individuals into a smaller number of clusters, while still satisfying the same variation requirements within each cluster. The proposed method can provide meaningful information about the head shape variation within a population, and should encourage ergonomist...

Nonlinear Finite Element and Post-Buckling of Large Diameter Thin Walled Tubes

This study investigates the crush behaviour of a relatively large diameter, thin walled tube through both experimental and finite element methods. The experiments were conducted using test specimens of cylindrical tube which were placed into a load press, and crushed by a distance of 150 mm. The thin walled tubes were found to collapse through localised buckling, with a folding layered mode of failure. Numerical analysis of the cylindrical tube was conducted using finite element (FE) methods through an explicit analysis (utilising a three dimensional shell model). Through the use of both ductile damage criteria and the Muschenborn–Sonne forming limit diagram (MSFLD), the model was able to initiate buckling failure without creating imperfections. The numerical model exhibited a similar layered, ring-folding mode of failure as observed in the experiment. Shear failure was also analysed, however caused a large amount of element distortion. The model showed a large degree of sensitivity to the coefficient of friction used in contact between the tube and the press. With the careful selection of mesh density, friction coefficient, and material properties, the FE model demonstrated very good correlation with the experiment in terms of critical buckling force and post-buckling response.

Experimental and Finite Element Nonlinear Dynamics Analysis of Formula SAE Impact Attenuator

Energy absorption and weight are major concerns in the design of an impact attenuator. To reduce the costs involved in the design and development of a new attenuator, it is important to minimise the time spent in the development and testing phase. The aim of this paper is to report on a study that used computer dynamic simulation to analyse the energy absorption and damage in a new impact attenuator. All initial requirements of the new attenuator were set in accordance with the 2011 Formula SAE rules. In this study, a nonlinear dynamic finite element was used to simulate an FSAE impact attenuator crash against a rigid barrier. Geometrical and material nonlinearities were performed using ABAQUS/Explicit commercial code. The numerical model was verified by experimental tests. Agreement between the numerical simulations and the test results showed that finite element analysis could be used effectively to predict the energy absorption and damage performance of an impact attenuator.