📚 IGCSE WJEC Engineering: Core Knowledge Essentials | IGCSE WJEC 工程：核心知识点梳理
This revision guide summarises the core knowledge areas for IGCSE WJEC Engineering. It covers design processes, materials, mechanical and electronic systems, manufacturing, quality, safety and sustainability. Each section pairs key ideas in English and Chinese to help bilingual learners review efficiently.
本复习指南汇总了 IGCSE WJEC 工程的核心知识领域，涵盖设计流程、材料、机械与电子系统、制造、质量、安全与可持续性。每一节以中英文对照呈现关键概念，帮助双语学习者高效复习。
1. The Engineering Design Process | 工程设计流程
Engineering design is not guesswork; it is a structured process that moves from a problem or need to a workable solution. In WJEC Engineering, you should be able to describe the design process as a cycle of research, specification, idea generation, development, modelling, testing, evaluation and improvement.
工程设计不是凭空猜测，而是从问题或需求出发形成可行方案的结构化过程。在 WJEC 工程中，你应当能够把设计流程描述为一个循环：调研、制定规格、产生想法、方案发展、建模、测试、评估与改进。
A design specification is a list of measurable criteria that the final product must meet, such as size, mass, cost, materials, safety and performance. Designers use tools like mood boards, annotated sketches, CAD drawings and physical models to communicate and refine their ideas.
设计规格是最终产品必须满足的一系列可测量标准，例如尺寸、质量、成本、材料、安全性和性能。设计者使用情绪板、标注草图、CAD 图纸和实物模型等工具来交流和优化设计方案。
- Iterative design means repeatedly testing and improving a prototype rather than expecting the first idea to work.
- 迭代设计 意味着不断测试和改进原型，而不是期望第一个方案就能成功。
- User-centred design focuses on the needs, abilities and limitations of the people who will use the product.
- 以用户为中心的设计 关注产品使用者的需求、能力和限制。
2. Materials and Their Properties | 材料及其性能
Choosing the right material is a core engineering decision. Materials are often grouped as metals, polymers, ceramics, composites and smart materials. Each group has characteristic mechanical, thermal, electrical and chemical properties that suit different applications.
选择合适的材料是工程设计的核心决策。材料通常分为金属、聚合物、陶瓷、复合材料和智能材料。每一类材料都有其特有的力学、热学、电学和化学性能，适用于不同场合。
Key mechanical properties include hardness, toughness, strength, elasticity, plasticity, ductility and brittleness. For example, steel is strong and tough, aluminium is light and corrosion-resistant, acrylic is transparent but brittle, and nylon is tough and self-lubricating.
关键力学性能包括硬度、韧性、强度、弹性、塑性、延展性和脆性。例如，钢强度高且韧性好，铝轻而耐腐蚀，亚克力透明但脆，尼龙韧性好且具有自润滑性。
| Material | 材料 | Typical property | 典型性能 | Example use | 典型用途 |
|---|---|---|
| Mild steel | 低碳钢 | Strong, tough, magnetic | 强度高、韧性好、有磁性 | Car bodies, beams | 车身、梁 |
| Aluminium alloy | 铝合金 | Low density, corrosion-resistant | 低密度、耐腐蚀 | Aircraft frames, cans | 飞机框架、易拉罐 |
| ABS | ABS 塑料 | Impact-resistant, easy to mould | 抗冲击、易成型 | Casings, LEGO bricks | 外壳、乐高积木 |
3. Forces, Stress and Strain | 力、应力与应变
When a force acts on a component, the material experiences stress. Stress is the force applied per unit cross-sectional area. It is calculated using the equation below, where force is in newtons (N) and area is in square metres (m²).
当力作用在构件上时，材料会承受应力。应力是单位横截面积上所承受的力。应力可用下式计算，其中力的单位是牛顿（N），面积的单位是平方米（m²）。
σ = F ÷ A
Strain is the change in length divided by the original length. It is a ratio and therefore has no units. Strain describes how much a material deforms under load.
应变是长度变化量除以原始长度。它是一个比值，因此没有单位。应变描述材料在载荷作用下变形的程度。
ε = ΔL ÷ L₀
The stiffness of a material is shown by Young’s modulus, which is stress divided by strain within the elastic limit. A stiff material such as steel has a high Young’s modulus; rubber has a low modulus and stretches easily.
材料的刚度由杨氏模量表示，它是在弹性极限内应力与应变的比值。钢等刚度大的材料杨氏模量高；橡胶的模量低，容易拉伸。
E = σ ÷ ε
4. Mechanical Systems and Mechanisms | 机械系统与机构
Mechanisms are used to change the type, direction, speed or size of motion and force. Common mechanical components include levers, linkages, gears, cams, pulleys, belts, chains and screws. You should be able to identify input, process and output in a mechanical system.
机构用于改变运动和力的类型、方向、速度或大小。常见机械构件包括杠杆、连杆、齿轮、凸轮、带轮、皮带、链条和丝杠。你应当能够识别机械系统中的输入、处理和输出。
Levers can provide mechanical advantage, which is the ratio of output force to input force. A Class 1 lever has the pivot between effort and load; a Class 2 lever has the load between pivot and effort; a Class 3 lever has the effort between pivot and load.
杠杆可以提供机械效益，即输出力与输入力的比值。一类杠杆的支点位于动力和负载之间；二类杠杆的负载位于支点和动力之间；三类杠杆的动力位于支点和负载之间。
- Gear ratio = number of teeth on driven gear ÷ number of teeth on driver gear. A ratio greater than 1 increases output torque but reduces speed.
- 齿轮比 = 从动轮齿数 ÷ 主动轮齿数。比值大于 1 会增大输出扭矩但降低转速。
- Pulley systems can multiply force; the mechanical advantage is approximately equal to the number of supporting rope sections.
- 滑轮系统 可以增大力；其机械效益约等于承载绳索的
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