📚 IGCSE Cambridge Engineering: High-Frequency Exam Topics & Common Mistakes | IGCSE 剑桥工程：高频考点与易错题分析
Cambridge IGCSE Engineering examinations reward candidates who can link theory to practical applications. This revision guide identifies the most frequently assessed topics, explains the underlying principles, and highlights the common mistakes that cause candidates to lose marks.
剑桥 IGCSE 工程考试侧重考查学生将理论与实际应用相结合的能力。本复习指南梳理最高频考点，解释基本原理，并指出导致考生失分的常见错误。
1. Materials and Mechanical Properties | 材料与机械性能
High-frequency questions ask you to select a suitable material for a given product and justify the choice using properties such as hardness, toughness, ductility, elasticity and tensile strength. You must be able to compare ferrous and non-ferrous metals, polymers, ceramics and composites in terms of their working properties.
高频考题常要求为给定产品选择合适的材料，并用硬度、韧性、延展性、弹性和抗拉强度等性能说明理由。你必须能够比较黑色金属、有色金属、聚合物、陶瓷和复合材料的工作性能。
A common error is to describe a material as 'strong' without stating the type of strength. For example, cast iron is strong in compression but weak in tension, while mild steel is tough and ductile. Another mistake is confusing hardness with toughness: a hard material resists surface indentation, but a tough material absorbs impact energy without fracturing.
常见错误是只写材料“强度高”而不说明强度类型。例如，铸铁抗压强度高但抗拉强度弱，而低碳钢坚韧且延展性好。另一个错误是混淆硬度与韧性：硬材料抵抗表面压痕，而韧材料吸收冲击能量而不断裂。
Tensile stress: σ = F ÷ A
抗拉应力：σ = F ÷ A
Strain: ε = ΔL ÷ L₀
应变：ε = ΔL ÷ L₀
Young modulus: E = σ ÷ ε
杨氏模量：E = σ ÷ ε
When selecting materials, always link at least two properties to the product function. For example, a crane hook needs high tensile strength to carry the load and toughness to resist sudden impact when lifting.
选择材料时，始终至少将两种性能与产品功能联系起来。例如，起重机吊钩需要高抗拉强度来承受载荷，同时需要韧性来抵抗起吊时的突然冲击。
2. Forces, Stress and Strain | 力、应力与应变
Calculations involving direct stress and strain appear regularly. You must convert all quantities to base SI units before substituting, and use cross-sectional area in m² when calculating stress in pascals.
涉及正应力和正应变的计算经常出现。代入前必须将所有量换算为基本 SI 单位，计算应力（单位为帕斯卡）时横截面积要使用平方米。
ulating the cross-sectional area of a circular specimen. For a circular rod, A = π × (d/2)
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