📚 Case Study Practical Exercises for Year 12 WJEC Engineering | 工程案例分析实战演练
Mastering case study analysis is essential for WJEC Year 12 Engineering students. Case studies bridge theoretical knowledge with real-world problem-solving, testing your ability to evaluate constraints, select materials, optimise processes, and justify design decisions. This article offers a structured approach to tackling case study questions, from initial reading to final report writing.
掌握案例分析对于 WJEC 12 年级工程学生至关重要。案例将理论知识与实际问题解决联系起来，考察你评估约束条件、选择材料、优化工艺并论证设计决策的能力。本文提供一套从初读到最终报告撰写的结构化应对方法。
1. Understanding the Case Study Context | 理解案例背景
Begin by reading the entire case study carefully, highlighting all numerical data, specifications, and stakeholder needs. Identify whether the scenario involves structural failure, energy systems, manufacturing inefficiency, or a new product design. Recognising the domain helps you select the right analytical tools.
一开始要仔细通读整篇案例，标出所有数据、规格和利益相关方需求。判断场景是涉及结构失效、能源系统、制造效率低下还是新产品设计。认清领域有助于你选择正确的分析工具。
Pay attention to the operating environment: temperature extremes, corrosive atmospheres, cyclic loading, or electrical interference all influence material and design choices. An offshore wind turbine anchor, for example, must withstand saltwater corrosion and dynamic wave loads, unlike a factory machine base.
注意运行环境：温度极值、腐蚀性气氛、循环载荷或电磁干扰都会影响材料和设计选择。例如，海上风机锚固需要抵抗盐水腐蚀和动态波浪载荷，不同于工厂机床底座。
2. Identifying Key Stakeholders and Requirements | 识别关键利益相关方与需求
Make a list of all parties affected: client, end user, maintenance team, regulatory authority, and the environment. Translate their needs into measurable engineering specifications, such as maximum deflection, target lifespan, or noise emission limits. These will become your design criteria.
列出所有受影响的群体：客户、最终用户、维护团队、监管机构和环境。将他们的需求转化为可度量的工程规格，例如最大挠度、目标寿命或噪声排放限值，这些将成为你的设计准则。
Use a requirements table to avoid missing constraints. For instance, a pedestrian bridge might require a live load capacity of 5 kN/m², a minimum clear width of 2.4 m, and a design life of 50 years. Always link requirements to evidence from the case.
使用需求表避免遗漏约束。例如，人行桥可能要求活荷载能力 5 kN/m²、最小净宽 2.4 m、设计寿命 50 年。务必把需求和案例证据联系起来。
3. Breaking Down the Problem | 问题分解
Decompose complex scenarios into smaller, manageable subsystems. A case about an automated production line might be split into mechanical structure, control electronics, sensor feedback, and pneumatic actuation. Analyse each subsystem separately before synthesising a holistic solution.
将复杂情境分解为较小、可管理的子系统。关于自动化生产线的案例可拆分为机械结构、控制电子、传感器反馈和气动执行。先分别分析各个子系统，再综合整体方案。
For a product failure case, apply a fault tree or ‘5 Whys’ approach. If a bracket fractured, ask why, tracing back from the crack surface to original material defect, insufficient fillet radius, or unexpected overload. This root-cause thinking mirrors WJEC marking expectations.
针对产品失效案例，运用故障树或“五个为什么”分析法。如果支架断裂，追问原因，从断口追溯到原始材料缺陷、圆角半径不足或意外过载。这种根本原因思维符合 WJEC 阅卷要求。
4. Data Analysis and Interpretation | 数据分析与解读
Engineering case studies often provide charts, tables, or sensor logs. Calculate key parameters such as stress, strain, power output, or efficiency. Always show the formula and conversion factors. For example:
工程案例通常提供图表、表格或传感器记录。计算关键参数，如应力、应变、功率输出或效率。始终写出公式和换算系数。例如：
σ = F / A
应力 σ = 力 F ÷ 截面积 A
When interpreting trends, comment on whether the data suggests linear, exponential, or fatigue behaviour. A plot of crack length versus cycles might indicate Paris’ law regime. Use yield strength and UTS values from material datasheets to assess whether a component operates within the safe zone.
解读趋势时，要说明数据是线性、指数还是疲劳行为。裂纹长度与循环次数的曲线可能指示 Paris 定律区间。利用材料数据表上的屈服强度和抗拉强度评估部件是否处于安全区。
| Material | Yield Strength σy (MPa) | Tensile Strength σUTS (MPa) |
|---|---|---|
| Mild Steel | 250 | 420 |
| Aluminium 6061-T6 | 276 | 310 |
| Titanium Ti-6Al-4V | 880 | 950 |
Table: Typical mechanical properties for comparison.
5. Material Selection in Context | 材料选择考量
Select materials by balancing strength, weight, cost, manufacturability, and environmental resistance. Use Ashby charts where available, but in exam conditions justify choices with property tables. A bicycle frame might move from steel to aluminium to carbon fibre depending on stiffness‑to‑weight ratio priorities.
选择材料时要平衡强度、重量、成本、可制造性和耐环境性。在考试中可利用性能表进行论证：取决于刚度-重量比的优先顺序，自行车车架可能从钢材转向铝材再转向碳纤维。
Quantify the benefit: an aluminium alloy with density 2.7 g/cm³ versus steel’s 7.85 g/cm³ can reduce weight by 65 % for the same volume. But consider galvanic corrosion if aluminium contacts steel in a marine environment. Such interdisciplinary analysis gains high marks.
量化效益：密度 2.7 g/cm³ 的铝合金对比钢材 7.85 g/cm³，相同体积可减重 65 %。但若在海洋环境中铝与钢接触，要考虑电偶腐蚀。这种跨学科分析能获得高分。
6. Manufacturing Process Evaluation | 制造工艺评估
Evaluate processes based on batch size, geometry complexity, tolerance requirements, and setup cost. For a prototype bracket, CNC milling is flexible; for mass production, die casting or stamping may be more economical. Always refer to the annual volume stated in the case study.
根据批量大小、几何复杂性、公差要求和启动成本评估工艺。对于原型支架，CNC 铣削灵活；而对于大批量生产，压铸或冲压可能更经济。始终参考案例中给出的年产量。
Consider the finishing and joining processes: welding affects heat‑affected zone properties, while adhesive bonding distributes stress but requires surface preparation. A gearbox housing might need machined mating surfaces after casting to achieve flatness within 0.05 mm.
考虑表面处理和连接工艺：焊接影响热影响区性能，而粘接分散应力但需要表面准备。变速箱壳体可能需要在铸造后机加工配合面，使平面度达到 0.05 mm 以内。
7. Cost-Benefit and Sustainability Analysis | 成本效益与可持续性分析
Estimate material cost per unit, labour, energy consumption, and tooling amortisation. A simple cost model could be:
Ctotal = Cmaterial + Clabour + (Ctooling / Nunits)
估算单件材料成本、人工、能耗和模具摊销。简单成本模型为：
总成本 = 材料成本 + 人工成本 + (模具成本 / 生产件数)
Sustainability arguments carry significant weight. Choose recyclable materials, minimise waste through near‑net‑shape manufacturing, or propose remanufacturing. A case involving electronic waste could be tackled by modular design for easier disassembly. Reference circular economy principles when appropriate.
可持续性论证占有较重权重。选择可回收材料，通过近终形制造减少废料，或提议再制造。涉及电子废弃物的案例可通过模块化设计便于拆解来解决。适当引用循环经济原则。
8. Risk Assessment and Mitigation | 风险评估与缓解
Identify failure modes using a simplified FMEA approach. For each component, list potential failure, effect, and cause, then propose mitigation. A pressurised vessel might fail due to fatigue cracking at weld toes; mitigation could be post‑weld heat treatment and regular ultrasonic inspection.
使用简化 FMEA 方法识别失效模式。对每个部件列出潜在失效、影响和原因，然后提出缓解措施。压力容器可能因焊趾处疲劳开裂而失效；缓解措施可以采用焊后热处理和定期超声检测。
Quantify risk where possible. If the probability of overload is 0.001 per year and consequence is ‘catastrophic’, the risk may be unacceptable. Introduce redundancy, fail‑safe features, or warning systems. A safety factor of at least 1.5 on yield strength is typical for static structures.
尽可能量化风险。如果过载概率为每年 0.001，后果为“灾难性”，风险可能不被接受。引入冗余、故障安全装置或报警系统。静态结构屈服强度安全系数通常至少取 1.5。
9. Design Proposal and Justification | 设计方案与论证
Present a clear, annotated sketch or describe the configuration in words. Highlight how your solution meets each specification. Use engineering terminology: ‘I‑beam cross‑section provides high second moment of area I for given mass, minimising deflection under bending.’
提供清晰的标注草图或口头描述构造。强调你的方案如何满足每项规格。使用工程术语：“工字梁截面在给定质量下提供高截面二次矩 I，最小化弯曲下的挠度。”
Justify choices with calculations. For a cantilever beam, state the maximum deflection formula:
δmax = (F L³) / (3 E I)
用计算来论证选择。对于悬臂梁，给出最大挠度公式：
最大挠度 δ = (F × L³) ÷ (3 × E × I)
Compare against the allowable deflection from the client brief. If your design has δmax = 2.1 mm while allowable is 3.0 mm, the solution is valid but perhaps over‑engineered; discuss weight reduction opportunities.
与客户任务书中的允许挠度对比。如果你的设计 δmax = 2.1 mm，而允许值为 3.0 mm，方案有效但可能过度设计；可讨论减重机会。
10. Effective Report Writing for Case Studies | 案例分析报告撰写技巧
Structure your answer logically: introduction, analysis, proposed solution, evaluation, and conclusion. Use headings and numbered steps. Even bullet points should be full sentences. Examiners reward clarity and logical flow.
有逻辑地组织答案：引言、分析、建议方案、评估和结论。使用标题和编号步骤。即使要点也要用完整句子。考官青睐清晰和逻辑流畅。
Integrate diagrams and tables where they add value. A sketch of the proposed assembly with leader lines labelling components can convey more than a paragraph. Ensure all axes on graphs are labelled with units.
在图表能增值的地方插入图示和表格。一张带有引出线标注部件的装配草图比一段文字传达更多信息。确保图表的坐标轴都标注单位。
11. Common Pitfalls and How to Avoid Them | 常见误区与避免方法
One common mistake is proposing a solution before fully analysing constraints. Always complete a thorough analysis first. Another is ignoring the ‘ilities’: manufacturability, maintainability, and sustainability. A elegant design that cannot be produced is worthless in an engineering case study.
常见错误是在充分分析约束之前就提出方案。务必先完成透彻分析。另一个错误是忽略“可…性”：可制造性、可维护性和可持续性。无法生产的精美设计在工程案例中毫无价值。
Students often forget to convert units (e.g., mm² to m²) leading to stress values off by orders of magnitude. Double‑check all conversions. Also, do not overlook non‑technical constraints such as budget ceilings or delivery deadlines mentioned in the brief.
学生常忘记单位换算（如 mm² 转 m²），导致应力值差几个数量级。复查所有换算。同时，不要忽视任务书中提到的预算上限或交付期限等非技术约束。
12. Practice Example: A Closer Look at a Product Failure | 实战案例：产品失效分析
Consider a case where an aluminium alloy connecting rod in a small engine fractured after 300 hours of service. The rod was designed for a maximum cyclic stress of 120 MPa. Examination revealed beach marks on the fracture surface, indicating fatigue. Root cause analysis showed a sharp machining mark at the transition radius, acting as a stress raiser.
考虑一个案例：小型发动机中的铝合金连杆在运行 300 小时后断裂。连杆设计最大循环应力为 120 MPa。断口检查显示海滩纹，表明疲劳。根本原因分析发现过渡圆角处存在尖锐加工刀痕，形成应力集中。
Remedial actions include polishing the radius, shot peening to introduce compressive residual stress, and switching to a forged blank with better grain flow. In your answer, estimate the stress concentration factor Kt using a chart and recalculate the local stress, showing it exceeds the fatigue limit. This mirrors real WJEC case study tasks.
补救措施包括抛光圆角、喷丸引入残余压应力、改用锻造毛坯改善流线。在你的回答中，利用图表估算应力集中系数 Kt，重新计算局部应力，证明其超过疲劳极限。这贴合真实的 WJEC 案例分析任务。
Published by TutorHao | Engineering Revision Series | aleveler.com
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