Abstract
AimsRoot tensile tests are often rejected if failure location is outside the middle section of samples. This study aims to identify where and why failure occurs along a root axis, and hence to revisit current approaches to test-validity.MethodsRoots from Festuca arundinacea; Lolium multiflorum; Lolium perenne were sampled from field-grown plants. Roots were tensile tested using a universal testing machine. Root samples were randomly allocated into two groups for testing. Group 1 roots were orientated with the older tissue closest to the top clamp, group 2 roots were orientated oppositely. Tensile strength, Young’s modulus and failure location were recorded for each sample.ResultsLolium multiflorum roots were thinner and stronger than roots of Festuca arundinacea. Failure location in tensile tests depended significantly on tissue age with 75% of samples failing in the younger third of root tissue regardless of the root orientation in the testing frame. Only 7% of roots failed in the middle third of the sample.ConclusionsFibrous roots tested in tension were observed to consistently fail in the younger tissue along the root axis. Exclusion of samples which fail outside the middle region of the root axis needs re-evaluation for a range of species.
Highlights
Root biomechanical properties are fundamental parameters to understand and quantify root mechanical reinforcement provided by vegetation to soil on slopes (Giadrossich et al 2017; Liang et al 2017; Mao et al 2012; Stokes et al 2009)
Tensile strength and Young’s modulus for roots with diameter between 0.1 and 7.0 mm are generally obtained by laboratory tensile testing, where a root segment is clamped at either end with tensile displacement until breakage occurs (Boldrin et al 2017; De Baets et al 2008; Giadrossich et al 2017; Loades et al 2013)
We propose that the exclusion of root samples which fail out with the middle region of the root samples during tensile testing is poorly justified, with failure occurring typically in the youngest region along the root axis
Summary
Root biomechanical properties are fundamental parameters to understand and quantify root mechanical reinforcement provided by vegetation to soil on slopes (Giadrossich et al 2017; Liang et al 2017; Mao et al 2012; Stokes et al 2009). Tensile strength and Young’s modulus are the most common biomechanical properties tested in bioengineering literature and are important inputs for predictive models of root mechanical reinforcement (Mao et al 2012; Pollen and Simon 2005; Schwarz et al 2013; Wu et al 1979). Tensile strength and Young’s modulus for roots with diameter between 0.1 and 7.0 mm are generally obtained by laboratory tensile testing, where a root segment is clamped at either end with tensile displacement until breakage occurs (Boldrin et al 2017; De Baets et al 2008; Giadrossich et al 2017; Loades et al 2013). Giadrossich et al (2020) combined laboratory tensile tests (root diameters: 1–4 mm) and field pull-out tests (root diameters: 5–57 mm) to quantify mechanical properties of Pinus radiata roots
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