Tabaracci Kaitlin, Vos Jacques, Robertson Daniel J
Department of Mechanical Engineering, University of Idaho, Moscow, ID, 83844, USA.
Plant Methods. 2024 Aug 14;20(1):125. doi: 10.1186/s13007-024-01253-9.
Stalk lodging (the premature breaking of plant stalks or stems prior to harvest) is a persistent agricultural problem that causes billions of dollars in lost yield every year. Three-point bending tests, and rind puncture tests are common biomechanical measurements utilized to investigate crops susceptibility to lodging. However, the effect of testing rate on these biomechanical measurements is not well understood. In general, biological specimens (including plant stems) are well known to exhibit viscoelastic mechanical properties, thus their mechanical response is dependent upon the rate at which they are deflected. However, there is very little information in the literature regarding the effect of testing rate (aka displacement rate) on flexural stiffness, bending strength and rind puncture measurements of plant stems.
Fully mature and senesced maize stems and wheat stems were tested in three-point bending at various rates. Maize stems were also subjected to rind penetration tests at various rates. Testing rate had a small effect on flexural stiffness and bending strength calculations obtained from three-point bending tests. Rind puncture measurements exhibited strong rate dependent effects. As puncture rate increased, puncture force decreased. This was unexpected as viscoelastic materials typically show an increase in resistive force when rate is increased.
Testing rate influenced three-point bending test results and rind puncture measurements of fully mature and dry plant stems. In green stems these effects are expected to be even larger. When conducting biomechanical tests of plant stems it is important to utilize consistent span lengths and displacement rates within a study. Ideally samples should be tested at a rate similar to what they would experience in-vivo.
茎倒伏（收获前植物茎杆过早折断）是一个长期存在的农业问题，每年造成数十亿美元的产量损失。三点弯曲试验和果皮穿刺试验是用于研究作物倒伏敏感性的常见生物力学测量方法。然而，测试速率对这些生物力学测量的影响尚未得到充分了解。一般来说，生物标本（包括植物茎杆）具有粘弹性力学特性是众所周知的，因此它们的力学响应取决于其偏转的速率。然而，关于测试速率（即位移速率）对植物茎杆的弯曲刚度、抗弯强度和果皮穿刺测量的影响，文献中几乎没有相关信息。
对完全成熟和衰老的玉米茎杆和小麦茎杆进行了不同速率的三点弯曲试验。还对玉米茎杆进行了不同速率的果皮穿刺试验。测试速率对三点弯曲试验得到的弯曲刚度和抗弯强度计算结果影响较小。果皮穿刺测量显示出强烈的速率依赖性效应。随着穿刺速率的增加，穿刺力降低。这是出乎意料的，因为粘弹性材料通常在速率增加时显示阻力增加。
测试速率影响完全成熟和干燥植物茎杆的三点弯曲试验结果和果皮穿刺测量。在绿色茎杆中，这些影响预计会更大。在进行植物茎杆的生物力学试验时，在一项研究中使用一致的跨度长度和位移速率很重要。理想情况下，样本应以与它们在体内所经历的速率相似的速率进行测试。
