📚 A-Level Eduqas Engineering: Case Study Practical Exercises | A-Level Eduqas 工程：案例分析实战演练
Case studies are at the heart of A-Level Eduqas Engineering, bridging theoretical principles with real-world problem solving. This practical exercise walks you through a complete analysis of a folding commuter bicycle, from initial design brief to final validation. By exploring material selection, structural calculations, manufacturing processes, and sustainability, you will develop the skills to tackle any engineering case study with confidence.
案例研究是 A-Level Eduqas 工程的核心，它将理论原理与现实问题解决相结合。本实战演练将带你完整分析一款折叠通勤自行车，从最初的设计概要一直到最终验证。通过探索材料选择、结构计算、制造工艺以及可持续性，你将培养自信应对任何工程案例研究的能力。
1. Introduction to the Case: Folding Commuter Bicycle | 案例介绍：折叠通勤自行车
Our client, a start-up called ‘UrbanFlow’, aims to launch a folding bicycle tailored for city dwellers who combine cycling with public transport. The primary function is to provide reliable, lightweight personal mobility that folds in under 15 seconds and weighs no more than 12 kg.
我们的客户是一家名为 ‘UrbanFlow’ 的初创公司，旨在推出一款专为结合骑行与公共交通的城市居民设计的折叠自行车。其主要功能是提供可靠、轻便的个人出行工具，折叠时间小于 15 秒，重量不超过 12 公斤。
The bike must accommodate riders up to 100 kg, fit within folded dimensions of 80 cm x 60 cm x 30 cm, and comply with the EN 14764 city bicycle safety standard. The target retail price is £400, requiring a unit manufacturing cost below £150 at a batch size of 5,000.
该自行车必须承载上限为 100 公斤的骑行者，折叠后尺寸在 80 cm x 60 cm x 30 cm 以内，并符合 EN 14764 城市自行车安全标准。目标零售价为 400 英镑，要求批量 5,000 台时单台制造成本低于 150 英镑。
A successful design must balance ergonomics, structural integrity, and manufacturability while minimising environmental impact. This case study uses these constraints to demonstrate a systematic engineering approach.
成功的设计必须在人体工学、结构完整性和可制造性之间取得平衡，同时最大程度降低环境影响。本案例研究利用这些限制条件来展示系统的工程方法。
2. Stakeholder Requirements and Design Brief | 利益相关者需求与设计概要
The primary stakeholders include commuters (end-users), UrbanFlow’s management, manufacturing partners, and regulatory bodies. End-users prioritise low weight, compact folding, ride comfort, and an affordable price. Management focuses on brand differentiation and profitability.
主要利益相关者包括通勤者（终端用户）、UrbanFlow 管理层、制造合作伙伴以及监管机构。终端用户优先考虑轻量化、紧凑折叠、骑行舒适度和亲民价格。管理层则关注品牌差异化和盈利能力。
Manufacturers demand designs that are easy to assemble with minimal specialised tooling; they prefer standard tube profiles and proven joining methods. Regulators require compliance with strength, braking, and lighting standards. All these voices shape the final design brief.
制造商要求设计便于组装，尽量减少专用工装；他们倾向于标准管材和成熟的连接方法。监管机构要求符合强度、制动和照明标准。所有这些声音共同塑造了最终的设计概要。
We summarised the design brief as: ‘Design a lightweight, foldable bicycle frame using a single-pivot mid-frame hinge. Integrate 20-inch wheels, a 7-speed hub gear, and disc brakes. Optimise the frame for aluminium alloy fabrication to meet mass and cost targets.’
我们将设计概要总结为：“设计一款采用单转轴中置铰链的轻量化可折叠自行车车架。集成 20 英寸车轮、7 速内变速花鼓和碟刹。针对铝合金制造优化车架，以满足质量和成本目标。”
3. Performance Specifications and Constraints | 性能规格与限制
Quantitative specifications translate the brief into measurable targets. Key metrics include total mass ≤ 12 kg, stiffness such that frame deflection under a 1 kN load is less than 3 mm, and a fatigue life exceeding 100,000 folding cycles.
量化规格将设计概要转化为可测量的指标。关键指标包括总质量 ≤ 12 公斤、在 1 kN 载荷下车架变形小于 3 毫米的刚度，以及超过 100,000 次折叠的疲劳寿命。
Environmental constraints mandate that 90% of components by mass must be recyclable. The paint and lubricants must be water-based to reduce volatile organic compounds. The bike must also withstand salt-spray testing for 96 hours without significant corrosion.
环境限制规定按质量计 90% 的部件必须可回收。油漆和润滑剂必须为水性，以减少挥发性有机化合物。自行车还必须承受 96 小时盐雾测试而不出现显著腐蚀。
Safety constraints derived from EN 14764 include a minimum frame yield strength of 350 MPa for critical load paths, effective braking from 25 km/h within 5.5 m on a dry surface, and reflectors integrated into the folded package without interference.
根据 EN 14764 制定的安全限制包括：关键载荷路径的车架最小屈服强度为 350 MPa，干燥路面上从 25 km/h 制动距离不超过 5.5 m，以及集成在折叠组件中且不发生干涉的反光器。
4. Material Selection Analysis | 材料选择分析
Material choice decisively influences weight, strength, cost, and recycling. We compared three candidate materials for the main frame tubes: 6061-T6 aluminium alloy, chromoly steel (4130), and carbon-fibre-reinforced polymer (CFRP).
材料选择决定性地影响重量、强度、成本和回收性。我们比较了三种主车架管材候选材料：6061-T6 铝合金、铬钼钢（4130）和碳纤维增强聚合物（CFRP）。
| Material | Yield strength (MPa) | Density (kg/m³) | Young’s modulus (GPa) | Cost index (£/kg) | Recyclability |
| 6061-T6 Al | 276 | 2700 | 69 | 3.5 | Excellent |
| 4130 Cr-Mo steel | 460 | 7850 | 205 | 2.0 | Very good |
| CFRP (UD, 60% fibre) | 800 (tensile) | 1550 | 70 | 20 | Difficult |
Aluminium 6061-T6 offers the best balance: it is one-third the density of steel with acceptable strength, and its recyclability aligns with sustainability goals. Steel’s higher weight would demand thinner walls, complicating welding. CFRP, while extremely light, costs too much and poses end-of-life disposal challenges.
6061-T6 铝合金提供了最佳平衡：密度仅为钢的三分之一，强度可接受，其可回收性与可持续发展目标一致。钢材较高的重量会要求更薄的管壁，使焊接复杂化。CFRP 虽然极轻，但成本过高，且带来报废处理难题。
For the hinge mechanism, stainless steel 17-4PH is selected for its high fatigue strength and corrosion resistance, even though it adds mass. The trade-off is justified by safety-critical function.
对于铰链机构，选择 17-4PH 不锈钢，因为它具有高疲劳强度和耐腐蚀性，尽管会增加质量。考虑到安全关键功能，这一权衡是合理的。
5. Structural Analysis: Frame and Hinge | 结构分析：车架与铰链
The main frame experiences bending and axial loads. We modelled the down tube as a simply supported beam with a central load from the rider’s weight. The maximum bending moment M for a central load P on a span L is PL/4.
主车架承受弯曲和轴向载荷。我们将下管建模为简支梁，承受来自骑行者重量的中心载荷。跨距 L 上中心载荷 P 产生的最大弯矩 M 为 PL/4。
Using P = 1200 N (including a 1.2 dynamic factor for the 100 kg rider) and L = 0.6 m, M_max = (1200 x 0.6)/4 = 180 Nm. The required section modulus Z = M/σ_allowable. For 6061-T6 with a safety factor of 1.5, allowable stress = 184 MPa.
取 P = 1200 N（包括 100 公斤骑行者 1.2 的动载荷系数），L = 0.6 m，M_max = (1200 x 0.6)/4 = 180 Nm。所需截面模量 Z = M/σ_allowable。对于 6061-T6，安全系数 1.5，允许应力 = 184 MPa。
Z = M_max / σ_allow = 180 Nm / (184 x 10⁶ Pa) = 9.78 x 10⁻⁷ m³ = 0.978 cm³
A tube of outer diameter 35 mm and wall thickness 2.5 mm gives Z ≈ 1.45 cm³, easily exceeding the minimum. This ensures rigidity and safety even after fatigue degradation.
外径 35 mm、壁厚 2.5 mm 的管材提供 Z ≈ 1.45 cm³，远超最低要求。这确保了即使在疲劳退化后仍具有刚度和安全性。
The hinge pin is checked for shear: double-shear area A = 2 x π(4 mm)² = 100.5 mm². With shear strength 350 MPa, failure load ≈ 35 kN, giving a safety margin above 20. FEM simulation confirmed peak von Mises stress below 100 MPa in the hinge region.
对铰链销进行剪切校核：双剪切面积 A = 2 x π(4 mm)² = 100.5 mm²。剪切强度 350 MPa，破坏载荷 ≈ 35 kN，安全裕度超过 20。有限元仿真确认铰链区域峰值 von Mises 应力低于 100 MPa。
6. Manufacturing Process Selection | 制造工艺选择
Production volume of 5,000 units per year suggests medium-series manufacturing. The aluminium frame tubes are cut, bent, and then TIG welded into sub-assemblies. TIG welding provides high-quality, ductile joints essential for cyclic loads.
年产 5,000 台的批量表明适合中等规模制造。铝合金管材经切割、弯曲后，使用 TIG 焊接成子组件。TIG 焊接可提供对循环载荷至关重要的高质量、韧性接头。
After welding, the frame undergoes heat treatment to T6 temper, restoring strength lost in the heat-affected zone. A CNC-machined hinge housing is bolted to the frame halves, allowing disassembly for repair. Surface finishing includes anodising for corrosion protection and aesthetic quality.
焊接后，车架经热处理至 T6 状态，恢复热影响区损失的强度。CNC 加工的铰链座用螺栓连接到车架两半，便于维修拆卸。表面处理包括阳极氧化，以实现防腐蚀和美观效果。
We chose low-pressure die casting for the handlebar stem and folding pedal arms due to their complex geometry and moderate strength requirements. This lowers per-part cost compared to full CNC machining while maintaining tight tolerances.
对于几何形状复杂、强度要求适中的车把立管和折叠脚踏臂，我们选择低压铸造。与全 CNC 加工相比，这降低了单件成本，同时保持了严格的公差。
7. Cost Estimation and Lifecycle Sustainability | 成本估算与生命周期可持续性
A detailed bill of materials (BOM) estimates the frame and hinge cost at £38 per unit, wheels and drivetrain at £42, and finishing/assembly at £18, summing to £98 variable cost. Fixed tooling amortised over 5,000 units adds £22, resulting in a factory cost of £120—well within the £150 target.
详细物料清单（BOM）估算车架和铰链成本为每台 38 英镑，车轮和传动系统 42 英镑，涂装/组装 18 英镑，可变成本合计 98 英镑。在 5,000 台上摊销的固定工装成本增加 22 英镑，出厂成本为 120 英镑——远低于 150 英镑的目标。
Sustainability analysis considers the entire lifecycle. Primary aluminium production is energy-intensive (≈15 kWh/kg), but using 60% recycled content reduces embodied energy by 70%. We specified closed-loop recycling for aluminium offcuts and designed for easy disassembly, with all fasteners accessible via standard hex keys.
可持续性分析考虑整个生命周期。原生铝生产能耗密集（≈15 kWh/kg），但使用 60% 的回收材料可将隐含能耗降低 70%。我们规定铝废料采用闭环回收，并设计为易于拆解，所有紧固件均可使用标准内六角扳手操作。
Transport weight per bike is compact, reducing shipping emissions. The product lifespan is projected at 8 years, after which the frame can be returned to the manufacturer for remelting—supporting a circular economy model.
每辆自行车的运输重量紧凑，减少了运输排放。产品寿命预计为 8 年，之后车架可返回制造商进行重熔——支持循环经济模式。
8. Prototyping and Testing Methods | 原型制作与测试方法
Alpha prototypes were built using CNC-bent aluminium tubes and 3D-printed PLA hinge housing for quick fit-check. Once geometry was validated, we fabricated three steel-6061 hybrid prototypes for structural testing.
阿尔法原型使用 CNC 弯管和 3D 打印 PLA 铰链座制造，用于快速装配检查。在几何形状验证后，我们制造了三台钢-6061 混合原型进行结构测试。
Static load testing applied 1,500 N to the seat post and bottom bracket concurrently. Deflections were measured with dial gauges and stayed below 1.8 mm—well within the 3 mm limit. The folding mechanism was cycled 120,000 times with pneumatic actuators; no cracks were detected.
静载荷测试同时对座管和五通施加 1,500 N。用百分表测量变形，保持在 1.8 mm 以下——远低于 3 mm 限制。折叠机构用气动执行器循环 120,000 次；未检测到裂纹。
Fatigue testing according to ISO 4210-6 simulated cobblestone and kerb impacts for 200,000 cycles. Dye penetrant inspection revealed zero defects. Finally, the complete bike passed the 96-hour salt-spray test with only superficial pitting.
按照 ISO 4210-6 进行的疲劳测试模拟鹅卵石路和路缘石冲击，循环 200,000 次。染料渗透检测显示零缺陷。最后，整车通过 96 小时盐雾测试，仅有表面点蚀。
9. Iterative Design Improvement | 迭代设计改进
Testing revealed that the original single-bolt seat clamp allowed slight rotation under high torque. We redesigned it to a two-bolt wedge system, increasing grip force by 40% without weight penalty. Finite element analysis confirmed a 30% reduction in contact stress.
测试发现，原始的单螺栓座管夹在高扭矩下会发生轻微旋转。我们将其重新设计为双螺栓楔形系统，增加了 40% 的夹紧力，且无重量增加。有限元分析证实接触应力降低了 30%。
User trials highlighted that the folding sequence was not intuitive; participants averaged 22 seconds instead of the target 15. We added colour-coded quick-release levers and numbered folding steps on a sticker near the hinge, cutting the average time to 13 seconds.
用户试用显示折叠顺序不够直观；参与者平均用时 22 秒而非目标的 15 秒。我们增加了颜色编码的快拆手柄，并在铰链附近粘贴编号折叠步骤贴纸，将平均时间缩短至 13 秒。
Weight crept to 12.3 kg in the pre-production build. By substituting a carbon-reinforced belt drive for the chain, we saved 0.4 kg and eliminated lubrication maintenance—but added £12 to the BOM. The client approved the change because of improved user experience.
预生产样车质量增至 12.3 公斤。通过用碳纤维增强皮带传动代替链条，我们减重 0.4 公斤并免除了润滑维护——但 BOM 增加了 12 英镑。客户因改善用户体验而批准了变更。
10. Presentation and Documentation | 展示与文档
As required by Eduqas coursework, we compiled an engineering report with clear headings: Specification, Research, Concept Development, Detail Design, Manufacturing Plan, Testing, and Evaluation. Each section includes diagrams, tables, and references to standards.
根据 Eduqas 课程要求，我们编写了一份工程报告，设置清晰的标题：规格、研究、概念开发、详细设计、制造计划、测试和评估。每个部分都包含图表、表格和标准引用。
We used Gantt charts to illustrate the project timeline and a risk assessment matrix to highlight failure modes such as hinge fracture or weld porosity. A costed BOM and an environmental impact summary were provided in the appendices.
我们使用甘特图说明项目时间线，并用风险评估矩阵突出诸如铰链断裂或焊接气孔等失效模式。附录中提供了成本核算物料清单和环境影响摘要。
The final presentation to stakeholders used renderings and physical test data. A real-time folding demonstration strengthened the business case. The project achieved sign-off, and the product moved to pilot production.
向利益相关方做的最终汇报使用了渲染图和物理测试数据。现场折叠演示增强了商业论证。项目获批，产品进入试生产阶段。
11. Conclusion: Lessons Learned | 结论：经验总结
This case study reinforces that successful engineering design is iterative and data-driven. Early material selection using Ashby charts narrowed options quickly; structural hand calculations validated FEA results, giving confidence before prototyping.
本案例研究强调，成功的工程设计是迭代且由数据驱动的。早期使用阿什比图进行材料选择可迅速缩小选项；手工结构计算验证了有限元分析结果，在原型制作前增强了信心。
Integrating sustainability from the start saved both cost and environmental impact. Clear documentation and stakeholder engagement were as important as technical solutions in bringing the product to market. Practise similar systematic analysis for any case study you encounter.
从一开始就融入可持续性，既节省了成本，也减少了环境影响。清晰的文档和利益相关者参与与技术解决方案同等重要，共同将产品推向市场。对遇到的任何案例研究，都应练习类似的系统分析方法。
Published by TutorHao | Engineering Revision Series | aleveler.com
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