结论：金属会变形给你看，复合材料不会
碳纤维车架的优势明确：同等强度下更轻。但它的损伤特性与金属有本质差别，而这个差别常被低估。
金属受到超出弹性范围的载荷会塑性变形——凹了、弯了，看得见。 这个变形本身是一种警示，使用者知道该检查了。
复合材料受到冲击时，表面可能完好，内部已经分层。 承载能力下降，而外部没有任何迹象。这种损伤被称为目视几乎不可检出的冲击损伤，是复合材料结构设计中的核心问题。
主要的损伤形式
| 损伤形式 | 成因 | 外观可见性 |
|---|---|---|
| 层间分层 | 冲击、疲劳 | 通常不可见 |
| 基体开裂 | 应力、温度循环 | 有时可见细微裂纹 |
| 纤维断裂 | 过载、严重冲击 | 严重时可见 |
| 界面脱粘 | 制造缺陷、湿热老化 | 不可见 |
| 表面磨损 | 使用磨蚀 | 可见 |
| 胶接失效 | 金属件与复合件连接处 | 部分可见 |
前两行和第四行是主要威胁，因为它们不可见却影响承载。
第六行值得单独说：碳纤维车架不可避免要与金属件连接（轴承座、快拆接口、脚踏安装点）。这些连接处是复合材料结构的薄弱环节——材料性能差异大、热膨胀系数不同、局部应力集中。实际失效中，连接处的比例不低。
为什么目视检查不可靠
冲击能量在复合材料中的传播方式与金属不同。金属通过塑性变形吸收能量，能量集中在撞击点附近；复合材料的能量会沿层间传播，在远离撞击点的位置造成分层。
所以可能出现的情况是：撞击点看起来只是蹭掉一点漆，而内部几厘米范围内已经分层。
对使用者而言，这意味着「看起来没事」不能作为判断依据。 这一点需要在说明书中明确告知，因为使用者会按金属产品的经验来判断。
检测手段的选择
| 手段 | 能发现什么 | 适用场景 |
|---|---|---|
| 目视 | 表面损伤、明显裂纹 | 日常检查，能力有限 |
| 敲击法 | 较大面积的分层 | 快速筛查，成本低 |
| 超声检测 | 分层、脱粘 | 较可靠，需要设备与人员 |
| 热成像 | 近表面缺陷 | 快速扫查较大面积 |
| X 射线 | 部分缺陷 | 对分层不如超声敏感 |
| 破坏性剖切 | 全部 | 抽检与失效分析 |
敲击法性价比较高，用小锤轻敲听声音差异，有分层的区域声音发闷。它能发现较大的分层，对小面积的不敏感，但成本几乎为零，适合作为日常检查手段。
设计上的应对
留损伤容限余量。 设计时假设结构会带有一定程度的不可见损伤，并保证在这种状态下仍满足强度要求。这是复合材料结构设计的常规做法，代价是重量优势被部分抵消。
在易受冲击的位置加保护。 底部、侧面等容易磕碰的部位，增加保护层或者改用金属件。
改善连接设计。 金属与复合材料的连接处避免集中受力，用面接触分散载荷，考虑不同材料的热膨胀差异。
设计可检性。 让关键部位便于检查，不要把重要的承载结构完全包在外壳里。
试验上的考虑
复合材料车架的试验安排与金属有几点不同：
冲击后必须做残余强度评估。 不能只判断冲击试验本身是否通过，要在冲击后测量剩余的承载能力。这是复合材料结构验证的核心内容。
湿热老化要考虑。 复合材料的基体对湿热敏感，长期使用后性能可能下降。建议做湿热老化后的性能对比。
疲劳试验的样本量要更多。 复合材料的性能分散性通常大于金属，单个样品的数据代表性较差。
检查手段要匹配。 试验过程中的中间检查，目视不够，需要用敲击或超声。
使用与售后的应对
说明书中应当包含：碳纤维件受到明显撞击后，即使外观完好也建议检查；哪些部位需要重点检查；发现什么现象应当停止使用；建议的检查周期。
售后方面，收到碳纤维产品的故障反馈时，应当询问是否发生过撞击，并对相关部位做专门检查，而不是只看故障表现的部位。
维修也是个问题。 复合材料的修补需要专门工艺，一般维修点做不了。产品设计时应当考虑：损坏的部件能否整体更换，而不是依赖现场修补。
成本与价值的权衡
碳纤维车架的成本明显高于铝合金，而带来的价值主要是减重。判断值不值，取决于使用场景：需要频繁搬运、装车的使用者，减重的价值很直接；主要在固定场所使用的，价值有限。
同时要把损伤容限的代价算进去：为了保证带损伤时仍安全，设计余量要留足，实际减重幅度往往小于理论值；加上检查和维修成本更高，全生命周期的账未必像初看那样划算。这个权衡应当基于目标使用者的真实需求来做。
与金属件的混合结构
多数碳纤维轮椅不是纯复合材料，而是复合材料与金属混用。这种混合结构的验证要额外关注界面：
胶接界面的强度与耐久；螺栓连接处的挤压与分层；不同材料热膨胀差异导致的内应力；以及电偶腐蚀——碳纤维与某些金属接触时会加速金属侧的腐蚀。
最后一项容易被忽略。 碳纤维是导电的，与铝直接接触且有电解质存在时，铝会被腐蚀。设计上应当有隔离措施，验证时应当做相应的加速腐蚀考察。
我们的做法
做复合材料车架的试验时，我们会在冲击类项目后增加检查环节，用敲击或其他手段确认有无不可见损伤，并在报告中记录。只做目视检查就进入下一项，可能带着已有损伤继续试验，后面的数据就失真了。
对于把碳纤维作为卖点的产品，建议补做冲击后残余强度试验——这项数据回答的是「磕了一下之后还能不能用」，对使用者是实质性的信息。
有需要可以把结构方案和铺层设计发过来一起确定检测范围，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，标准信息见标准查询。
English version
Conclusion. Carbon composite frames offer a clear advantage in weight for a given strength. Their damage behaviour differs fundamentally from metal, however, and that difference is routinely underestimated. Metal loaded beyond its elastic range deforms plastically: it dents, it bends, and the deformation is visible. That visible change is itself a warning that inspection is due. A composite struck by an impact may look intact on the surface while delaminating internally. Load-carrying capacity falls with no external sign. This is known as barely visible impact damage and it is the central problem in composite structural design.
Damage modes. Interlaminar delamination from impact or fatigue is generally invisible. Matrix cracking from stress or thermal cycling is sometimes visible as fine cracks. Fibre fracture from overload or severe impact is visible when severe. Interfacial debonding from manufacturing defects or hygrothermal ageing is invisible. Surface abrasion from use is visible. And adhesive joint failure where metal fittings meet composite is partly visible.
The invisible modes are the main threat because they reduce capacity without warning. Joints deserve separate mention: a composite frame must connect to metal parts at bearing housings, quick-release interfaces and footrest mountings, and these are weak points because material properties differ, thermal expansion differs and stress concentrates locally. Joints account for a significant share of real failures.
Why visual inspection is unreliable. Impact energy propagates differently in composites. Metal absorbs energy through plastic deformation, concentrating it near the point of impact. In composites, energy travels along interfaces and produces delamination some distance away. The result is that an impact point may show only scuffed paint while delamination extends several centimetres internally. For users this means that looking undamaged is not a basis for judgement, a point that must be stated explicitly in the instructions, because users will apply their experience of metal products.
Detection methods. Visual inspection finds surface damage and obvious cracks, and is limited. Tap testing finds larger delaminations, offers a quick low-cost screen, and works by listening for the duller sound over a delaminated area; it is insensitive to small areas but costs essentially nothing and suits routine checking. Ultrasonic inspection reliably finds delamination and debonding but requires equipment and trained personnel. Thermography scans larger areas quickly for near-surface defects. Radiography detects some defects but is less sensitive to delamination than ultrasound. Destructive sectioning finds everything and suits sampling and failure analysis.
Design responses. Build in damage tolerance margin, assuming the structure carries some invisible damage and still meets strength requirements; this is standard practice for composite structures and partly offsets the weight advantage. Protect impact-prone areas such as the underside and flanks, with additional plies or metal components. Improve joint design by distributing load over area rather than concentrating it and by accounting for differential thermal expansion. And design for inspectability, keeping critical load-bearing structure accessible rather than fully enclosed.
Testing considerations. Residual strength after impact must be evaluated; judging the impact test alone is insufficient, and remaining load capacity must be measured, which is the core of composite structural verification. Hygrothermal ageing should be considered, since the matrix is sensitive to heat and moisture and properties may decline in service, so comparative testing after ageing is worthwhile. Fatigue testing needs larger sample sizes, because composite property scatter generally exceeds that of metals. And inspection methods during testing must match the material: visual checking between items is not sufficient and tap or ultrasonic methods are needed.
Use and service. Instructions should state that composite parts subjected to a noticeable impact should be inspected even when they appear undamaged, identify the areas to check, describe symptoms warranting removal from service, and recommend an inspection interval. In service, when a fault is reported on a composite product, ask whether an impact occurred and inspect the relevant areas specifically rather than only where the symptom appears. Repair is a further issue: composite repair requires specialist technique beyond most service points, so design should allow damaged components to be replaced as units rather than relying on field repair.
How we handle it. For composite frames we add an inspection step after impact items, using tap testing or other means to confirm whether invisible damage exists, and we record the result. Proceeding to the next item on the basis of visual inspection alone risks continuing with damage already present, which distorts the subsequent data. For products sold on their composite construction we suggest adding a residual strength after impact test, since that answers whether the product remains usable after a knock, which is substantive information for the user.
Send us the structural concept and layup design and we will define the scope. Phone or WeChat: +86 132 4819 8029.