ISO 16840-2:2007 load deflection and hysteresis measurements for a sample of wheelchair seating cushions

Abstract

Load deflection and hysteresis measurements were made on 37 wheelchair seating cushions according to ISO 16840-2:2007. Load deflection plots for all 37 cushions are reported and fundamental aspects of graph interpretation discussed. ISO hysteresis data are also reported and interpretation discussed.

Correlation of ISO 16840-2:2007 impact damping and hysteresis measures for a sample of wheelchair seating cushions

“…(Hollington et al, 2014). However there is also a need for scientific data about the performance of seating support surfaces in order that objective comparisons can be made.…”

“…(Hollington et al, 2014) The aim of this study is to examine the relationship between two of the tests defined in the standard. The first test, load deflection and hysteresis* from section 9 of the standard, describes the compression and recovery characteristics of the cushion as it is subjected to various loads for a duration of 120 s. The second test is the impact damping test from section 11 of the standard, and takes a different approach to measuring the response of the cushion under loading conditions on a much shorter time scale.…”

“…It is also further stated in the standard that "Cushions with larger hysteresis values will tend to absorb energy when used on rough surfaces or when dropping down steps, rather than transfer the impact energy to the user's tissues" (ISO, 2007) which implies the relevance of the hysteresis measure to the impact response of the cushion. Sprigle et al (2010) (Hollington et al, 2014) A comparison between ISO16840-2 hysteresis and impact damping tests would help inform this statement and the rationale.…”

“…(Sprigle, 2010) However, the reports also highlight that a few issues need to be addressed in the ISO standard test methodology in order to ensure this repeatability. Additionally, certain additional data should be reported for improved interpretation of the test (Sprigle, 2010) (Chung, 2009 (Hollington et al, 2014). However, it has also been highlighted that this test must be carefully considered in order to avoid misinterpretation of results in relation to the rationale linked to them.…”

“…"Wheelchair seating cushions must fulfil a variety of requirements in order to meet an individual's specific rehabilitation aims including managing comfort, tissue integrity, postural control, postural alignment and functional enablement." (Hollington et al, 2014) The information available to clinicians when selecting a seating support surface include experience, the theory behind support surfaces, knowledge of material properties, user trials and, if available, interface pressure mapping (IPM) technologies. Unless IPM can be utilised, no scientific data are available for decision making when it comes to comparing the vast range of cushions commercially available.…”