Key term
CCEA A-Level Technology and Design 8900
Material Selection and Wood
Metals
Plastics
Composite and Emerging Materials
Processing Materials
Product Analysis and Design Communication
Design for Manufacture, Quality and Safety
Electronic Control SystemsOption A
Topic overviewControl systems, feedback and electronics safetyResistors, Ohm's law and power ratingsCapacitors and RC timingPotential dividers, sensors and comparatorsSwitches, pull-up and pull-down resistorsOutput devices and LEDsTransistors, Darlington pairs and thyristorsLogic gates, truth tables and flip-flops555 monostable and astable timers
Microelectronic Control SystemsOption A
Topic overviewMicrocontroller systems, ADCs and DACsStrain gauges and bridge circuitsOptical switches, encoded discs and Schmitt triggersOp-amp amplifiers and gainZener diodes and voltage regulatorsKarnaugh maps and binary countersSeven-segment, LCD and dot matrix displaysPIC flowcharts and programmingDC motors, stepper motors and driver circuits
Mechanical and Pneumatic ComponentsOption B
Topic overviewOpen and closed loop mechanical and pneumatic controlSafe working with compressed air and mechanismsLevers, linkages and momentsGear types and gear trainsPulleys, belts, chains and shaft fixingsCams, cranks and converting motionCompressed air supply and pneumatic valvesCylinders, shuttle valves, restrictors and reservoirsPneumatic circuits for logic, timing and speed control
Mechanical and Pneumatic SystemsOption B
Topic overviewHydraulics, system limitations and plant safetyTorque, work, power and air consumptionVacuum handling, proximity sensors and 5/3 valvesSequential and cascade pneumatic circuitsCam profiles and follower displacement diagramsGear geometry, pulley blocks and ratchetsToggles, treadles, shafts and couplingsFriction, brakes and clutchesBearings, lubrication and seals
Designing and Manufacturing ProductsOption C
Topic overviewResearch, questionnaires and specificationsIdea generation, critiques and computer simulationManufacturing planning and product evaluationCFRP, GRP, Kevlar and tungsten carbideSmart materials, nanotechnology and biophotovoltaicsIsometric, perspective and assembly drawingLaminating, steam bending, cutting and printing processesRisk assessment and product safety lawScales of production, JIT and cell productionQuality assurance, ISO 9001 and continuous improvementDesign influences and intellectual property rights
Product Design in Industry and SocietyOption C
Topic overviewLife-cycle environmental impact and climate changeThe 6Rs, waste and environmental legislationSustainable metals, plastics and degradable polymersProduct life cycles, consumer types and relaunchesCAD, CAM, 3D scanning and quick-change mouldingMarket pull, technology push and market strategyPrice, place and promotionJigs, fixtures and ICT in quality controlDesign for maintenance, inclusion and scale productionRendering, typography and presentationDyson, Baylis, Memphis and Apple
Product Development
Product and System Design and Manufacture
Design for Manufacture, Quality and Safety
Factor of safety and tolerances
- 3 things to know
- AS 1 Paper 1
Overview
Factors of safety with worked failure loads and stress, why aircraft and lifts differ, limits and tolerances, clearance and interference fits, and tolerance stack-up.
What you need to know
Answer each one before you reveal it.
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Key term
Explain why designers cannot simply design to the exact working load.
Key term
A bracket fails at a load of 3,000 N and carries a working load of 750 N. What is its factor of safety?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is a factor of safety?
Model answer
A factor of safety is the ratio of the load that would cause failure to the maximum load expected in use. A factor of 3 means a part could carry three times its working load.
- 2
Explain why designers cannot simply design to the exact working load.
Model answer
Materials vary and may contain hidden flaws. Loads in use can exceed estimates through misuse or impact, and wear and corrosion weaken parts over time.
- 3
A bracket fails at a load of 3,000 N and carries a working load of 750 N. What is its factor of safety?
Model answer
The factor of safety is 4. The working is 3,000 ÷ 750 = 4.
- 4
A lifting sling breaks at 25 kN and is used with a factor of safety of 5. What is its safe working load?
Model answer
The safe working load is 5 kN. The working is 25 ÷ 5 = 5 kN.
- 5
A shelf bracket must carry 400 N with a factor of safety of 3. What failure load must it be designed for?
Model answer
The bracket must withstand at least 1,200 N before failing. The working is 400 × 3 = 1,200 N.
- 6
A rod with a cross-sectional area of 50 mm² carries a tensile load of 2,000 N, and its material fails at a stress of 240 N/mm². What is the factor of safety?
Model answer
The factor of safety is 6. The working is stress = 2,000 ÷ 50 = 40 N/mm², and 240 ÷ 40 = 6.
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