结论：拐杖的失效多数是疲劳失效，而疲劳只能靠循环试验暴露

拐杖、手杖在每一步行走中都承受一次加载和卸载。按每天行走数千步计算，使用几年的累计循环次数非常可观。

在这种工况下，主要的失效机理是疲劳 ——材料在远低于静态强度的应力下，经过足够多的循环后产生裂纹并最终断裂。

静载试验合格的产品，疲劳试验可能不合格。 所以只做静载强度而不做疲劳，对这类产品是不充分的。

受力的特点

冲击性。 每一步落地时是冲击加载，峰值力大于静态体重的分量。

偏心。 力的作用线与管件轴线通常不重合，产生弯矩。这是应力集中的来源。

方向变化。 行走中拐杖的倾角不断变化，受力方向随之变化。

高循环次数。 前面提过。

意外的大载荷。 使用者失去平衡时，拐杖可能承受远超正常的力。

「偏心产生弯矩」是理解拐杖受力的关键。 拐杖不是纯轴向受压的杆件，弯曲应力往往是决定疲劳寿命的因素，而弯曲应力集中在结构变化的位置——销孔、弯折处、焊缝、把手连接处。

疲劳试验的设计

要素 设定依据
载荷大小 按额定体重与步态峰值系数
加载方向 模拟实际使用角度
循环次数 按预期使用年限折算
加载频率 不宜过高，避免发热影响
调节位置 在最长位置做（最不利）
失效判据 断裂、裂纹、旷量超限、功能异常

加载方向的设定很关键。 纯轴向加载测出来的寿命会明显高于带倾角的加载，而实际使用中拐杖总是有倾角的。建议按实际的使用角度加载。

失效判据不应只看断裂。 旷量增大、锁定失效、把手松动都是实际的失效，虽然还没断。

易失效的位置

实际的疲劳裂纹常出现在：

销孔周围。 孔的边缘是应力集中点。

弯折处。 腋拐的弯曲段。

焊接与连接处。 材料性能变化的位置。

管件直径变化处。 内外管过渡。

把手安装位置。 集中受力。

脚垫连接处。 反复受冲击。

这些位置在试验后应当重点检查，用目视或者必要时用无损方法查看有无裂纹。只看有没有断是不够的 ——已经开裂但未断的产品实际上已经失效了。

材料与结构的考虑

材料的疲劳性能。 不同材料的疲劳特性差别大。某些材料存在疲劳极限，低于该应力可以近似无限次循环；另一些材料没有明确的疲劳极限，应力越低寿命越长但始终有限。

应力集中的缓解。 孔边倒角、过渡圆角、避免尖锐缺口。

壁厚与直径的搭配。 在重量允许的范围内增加抗弯能力。

表面质量。 划痕和加工缺陷是疲劳裂纹的起点，表面处理质量影响疲劳寿命。

腐蚀的影响。 腐蚀环境会明显降低疲劳寿命，两者是叠加的。

最后一条值得注意。 单独做疲劳试验和单独做腐蚀试验都合格的产品，在腐蚀环境下的疲劳寿命可能明显低于干燥环境。对于长期使用且可能接触潮湿的产品，建议考虑这个叠加效应。

脚垫的管理

脚垫是拐杖上磨损最快的部件，也是防滑的关键：

磨损。 橡胶脚垫会逐渐磨平，防滑性能下降。

老化。 橡胶随时间硬化，湿态摩擦性能下降。

脱落。 与管件的配合松动后可能脱落。

磨损指示。 建议设计磨损指示——磨到某个标记就该换。这把判断从主观变成客观。

更换的便利性。 应当便于使用者自行更换，并能单独购买。

湿态防滑。 前面讲过，干燥与潮湿条件下的防滑性能差别很大，两种条件都应当测。

「磨损指示」这个设计值得推广。 使用者通常不知道脚垫磨到什么程度该换，有明确的标记之后判断就简单了。

使用与检查

说明书应当包括：适用体重；正确的高度调节；使用姿势；日常检查要点；脚垫的检查与更换；以及出现什么情况应当停用。

日常检查的要点建议包括： 脚垫的磨损程度；管件有无变形或裂纹；调节机构是否可靠；把手是否松动；以及各连接处是否牢固。

「管件有无裂纹」这一项可以给出检查位置的提示 ——销孔周围、弯折处这些易发位置。使用者不会主动查，但如果资料指出了具体位置，检查就变得可行。

试验样品与数量

疲劳试验的结果有较大的分散性，样品数量影响结论的可靠性：

单个样品的结果代表性不足。 材料和制造的差异会导致寿命差别明显。

建议多个样品。 具体数量按要求和实际情况确定。

样品应当是量产状态。 试制样品的工艺可能与量产不同，特别是焊接和表面处理。

记录样品信息。 批号、生产日期、生产线。

保留失效样品。 失效样品用于分析失效位置和形态，对改进有价值。

最后一条实务中常被忽略。 试验结束后样品被丢弃，失效分析的机会也就没了。建议保留并拍照记录失效形态。

使用者体重与安全余量

拐杖的额定体重设定要考虑实际情况：

实际使用者可能超重。 声称的体重上限如果偏低，超载使用的情况会发生。

冲击放大。 步态中的峰值力大于体重，倍数与步态和行走速度相关。

单侧承载。 使用一侧拐杖时，该侧承担的比例较高。

意外载荷。 失去平衡时的瞬时载荷可能远超正常。

建议额定体重的设定留出余量，并在产品上清晰标注上限。标注不清的产品，超载使用的概率明显更高，而超载会显著缩短疲劳寿命。

我们的做法

做拐杖类产品测试时，我们会按实际使用角度做疲劳加载，并在调到最长位置的状态下做，因为这两点都对应实际中最不利的情形。

试验结束后，我们不只看有没有断裂，还会检查易发位置有无裂纹，并测量旷量的变化。已经开裂但未断的产品，实际上寿命已经到了。

如果你有拐杖或手杖类产品需要安排疲劳验证，想先理清试验条件，可以把产品结构和参数发过来一起讨论，或者直接联系：132 4819 8029。检测能力见服务介绍，产品分类见手动轮椅检测与电动轮椅检测，案例见案例。

English version

Conclusion. Crutches and walking sticks are loaded and unloaded once at every step. At several thousand steps a day, the cumulative cycle count over years of use is considerable. Under that duty the principal failure mechanism is fatigue: a crack initiates and eventually propagates to fracture at stresses well below the static strength. A product passing static load testing may fail fatigue testing, so static strength testing alone is inadequate for these products.

Loading characteristics. Loading is impulsive, since each footfall applies an impact whose peak exceeds the static share of body weight. Loading is eccentric, since the line of force usually does not coincide with the tube axis, producing a bending moment and hence stress concentration. Direction varies, since the crutch angle changes continuously during walking. Cycle counts are high, as noted. And occasional large loads occur when the user loses balance and the crutch carries far more than normal. Eccentricity is the key to understanding crutch loading: a crutch is not a purely axially compressed strut, and bending stress usually governs fatigue life, concentrating where the structure changes at pin holes, bends, welds and handle attachments.

Designing fatigue tests. Load magnitude follows rated user weight and a gait peak factor. Load direction simulates actual angles of use. Cycle count converts from the expected service life. Loading frequency should not be excessive, to avoid heating effects. The adjustment position should be the longest, being least favourable. And failure criteria should cover fracture, cracking, excessive play and functional abnormality. Load direction matters greatly: purely axial loading yields markedly longer life than angled loading, while a crutch in use is always angled, so load at realistic angles. Failure criteria should not be limited to fracture either, since increased play, locking failure and handle loosening are genuine failures even without breakage.

Where failures occur. Fatigue cracks commonly appear around pin holes, where the hole edge concentrates stress; at bends, in the curved section of an underarm crutch; at welds and joints where material properties change; at diameter transitions between inner and outer tubes; at handle attachments, where load concentrates; and at ferrule attachments, subject to repeated impact. Inspect these locations after testing, visually and where necessary by non-destructive methods, since checking only for fracture is insufficient: a product already cracked but not broken has effectively failed.

Material and structural considerations. Fatigue properties vary widely between materials, with some exhibiting a fatigue limit below which cycling is effectively unlimited and others having no definite limit, so that lower stress extends life without making it infinite. Stress concentration can be relieved through chamfered hole edges, generous transition radii and avoidance of sharp notches. Wall thickness and diameter should be matched to increase bending capacity within the weight allowance. Surface quality matters because scratches and machining defects initiate fatigue cracks, so surface treatment quality affects life. And corrosion markedly reduces fatigue life, the two acting together. The last deserves attention: a product passing fatigue testing and corrosion testing separately may show substantially shorter fatigue life in a corrosive environment than in dry conditions, so consider the combined effect for products in long-term use that may encounter moisture.

Managing ferrules. The ferrule wears fastest and provides the grip. Wear flattens rubber ferrules and reduces grip. Ageing hardens rubber and reduces wet friction. Loosening can lead to the ferrule coming off. A wear indicator is worth designing in, so that replacement is due at a visible mark, converting a subjective judgement into an objective one. Replacement should be easy for the user and ferrules should be separately purchasable. And wet grip must be tested as well as dry, since performance differs greatly. The wear indicator deserves wider adoption: users generally do not know how worn is too worn, and a clear mark makes the judgement simple.

Use and inspection. Instructions should state the weight limit, correct height adjustment, posture in use, daily check points, ferrule inspection and replacement, and when the product should be withdrawn. Daily checks should include ferrule wear, deformation or cracking of tubes, reliability of the adjustment mechanism, handle tightness and security of connections. Give locations for the crack check, such as around pin holes and at bends, since users will not look unprompted but will check if told where.

How we handle it. For walking aids we apply fatigue loading at realistic angles of use and with the product at its longest adjustment, both corresponding to the least favourable real conditions. After testing we look beyond fracture, inspecting the crack-prone locations and measuring the change in play, because a product cracked but not broken has already reached the end of its life.

Send us the construction and parameters and we will work out the test conditions. Phone or WeChat: +86 132 4819 8029.