Brazil nut (Bertholletia excelsa) fruits are capable of resisting high mechanical forces when released from trees as tall as 50 m, as well as during animal dispersal by sharp-teethed rodents. Thick mesocarp plays a crucial part in seed protection. We investigated the role of microstructure and how sclereids, fibers, and voids affect nutshell performance using compression, tensile and fracture toughness tests. Fractured specimens were analyzed through scanning electron microscopy (SEM) and microtomography (microCT). Mesocarp showed high deformability (strain at max. stress of ~30%) under compression loading, a critical tensile strength of ~24.9 MPa, a Weibull modulus of ~3, and an elastic modulus of ~2 GPa in the tensile test. The fracture toughness, estimated through the work of fracture of SENB tests, reached ~2 kJ/m². The thick and strong walls of mesocarp cells, with a weaker boundary between them (compound middle lamella), promote a tortuous intercellular crack path. Several toughening mechanisms, such as crack deflection, breaking of fiber bundles, fiber pullout and bridging as well as crack branching, occur depending on how fiber bundles and voids are oriented.

巴西坚果（Bertholletia excelsa）水果在从高至50 m的树木中释放时以及在尖齿啮齿动物传播动物的过程中都能够抵抗较高的机械力。中厚果皮在种子保护中起着至关重要的作用。我们使用压缩，拉伸和断裂韧性测试研究了微结构的作用以及硬化骨，纤维和空隙如何影响螺帽性能。通过扫描电子显微镜（SEM）和显微断层扫描（microCT）分析断裂的标本。中果皮在压缩载荷下表现出较高的变形能力（最大应力为〜30％时的应变），临界拉伸强度为〜24.9 MPa，威布尔模量为〜3，弹性模量为〜2 GPa。通过SENB测试的断裂功估算的断裂韧性达到〜2 kJ / m ²。中果皮细胞的厚而坚固的壁（它们之间的边界较弱）（复合中间层）促进了曲折的细胞间裂纹路径。根据纤维束和空隙的定向方式，会出现几种增韧机制，例如裂纹挠曲，纤维束断裂，纤维拉出和桥接以及裂纹分支。