79 exam-style questions on Material selection — topic B3.1 of Design in practice in the IB Design Technology syllabus — with answers and explanations. Samples below; the full set is free with an account.
A climbing panel for an unsupervised outdoor playground must survive ten years of ultraviolet exposure and rain, be cleaned of graffiti with solvent, and never splinter. Which material best meets these constraints?
Answer: High-density polyethylene sheet with UV stabiliser
The panel is wet, sunlit, cleaned with solvent and unsupervised, so it must be a homogeneous polymer that absorbs no water and cannot splinter. Wood-based boards and painted steel all fail once the surface film is broken.
A removable seal for a vacuum flask lid must stay flexible from −20 °C to 120 °C, be washed in a dishwasher many times and be in direct contact with drinks. Which material should be specified?
Answer: Food-grade silicone elastomer
Silicone keeps its elasticity across a very wide temperature range, is unaffected by repeated hot washing and is available in food-contact grades. PVC relies on plasticisers that can migrate, natural rubber degrades and polystyrene deforms in a hot wash.
A chef's knife blade must hold a sharp edge through daily use, be hardened by heat treatment and resist staining by acidic foods in a busy kitchen. Which material should be selected?
Answer: High-carbon martensitic stainless steel
Only a martensitic stainless steel combines enough carbon to be hardened for edge retention with the chromium needed to resist acidic foods. The 304 grade resists corrosion but cannot be hardened, and aluminium and mild steel fail on edge retention or staining.
A school specifies a garden bench that will stay outdoors all year, receive no annual treatment and last at least fifteen years. Which timber-based material should be selected?
Answer: Naturally durable oak heartwood, left untreated
With no maintenance the timber must be durable in itself, which points to the heartwood of a naturally durable species. Fibreboard and interior plywood delaminate once moisture reaches the adhesive, and untreated spruce decays within a few seasons.
A casing for a mains-powered power tool will be injection moulded in 50 000 units a year. It must stay tough when the tool is dropped on a site floor, hold its shape next to a motor running at 90 °C, and mould with integral screw bosses and a textured surface. Which material should be selected?
Answer: Acrylonitrile butadiene styrene (ABS)
ABS is tough under impact, holds its shape up to roughly 100 °C and moulds crisply, so bosses and texture come straight off the tool. Low-density polyethylene is too soft and flexible for a rigid casing and softens near the motor temperature, polystyrene is brittle under impact, and cast acrylic sheet is not an injection moulding material at all.
A commuter bicycle frame will be made in 20 000 units a year. It must resist corrosion without being painted, be welded on an open production jig rather than inside a sealed inert-gas chamber, and keep the material and processing cost per frame low at this volume. Which material should be selected?
Answer: 6000-series aluminium alloy tubing, welded
The aluminium alloy is welded on an open jig with only the local argon shield from the torch, forms its own protective oxide film so no paint is needed, and is far cheaper than titanium or carbon fibre at this volume. Carbon fibre cannot be welded at all, titanium must have the whole hot joint enclosed in inert gas and costs far more, and steel would have to be painted to survive.
That was 6 of 79 Material selection questions.
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79 Material selection questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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