{ "node": { "id": "term:thermal-stress", "type": "Term", "label": "Thermal stress", "properties": { "id": "thermal-stress", "name": "Thermal stress", "section": "topic-thermal", "definition": "Mechanical stress caused by a temperature change when a part cannot expand freely or is joined to a material that expands differently. A fully restrained aluminium bar warmed by 50 K would carry about 80 MPa. Repeated cycles fatigue welds, solder joints and adhesive bonds, which is what thermal shock testing sets out to provoke.", "formula": "σ = E·α·ΔT", "unit": "Pa", "related": [ "thermal-expansion-coefficient", "thermal-shock-test", "glass-transition-temperature", "structural-adhesive", "busbar" ], "example": { "title": "Compare free and constrained expansion", "text": "An illustrative fully constrained linear elastic material with E = 2 GPa, expansion coefficient 50×10⁻⁶/K and ΔT = 20 K has EαΔT = 2 MPa. A freely expanding part does not develop this stress from uniform heating alone." }, "url": "https://lemonergy.com/learn/glossary/thermal-stress/", "mentions": [] } }, "edges": [ { "id": "edge:4661", "source": "term:thermal-stress", "target": "topic:topic-thermal", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:4662", "source": "term:thermal-stress", "target": "term:thermal-expansion-coefficient", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4663", "source": "term:thermal-stress", "target": "term:thermal-shock-test", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4664", "source": "term:thermal-stress", "target": "term:glass-transition-temperature", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4665", "source": "term:thermal-stress", "target": "term:structural-adhesive", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4666", "source": "term:thermal-stress", "target": "term:busbar", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4667", "source": "term:thermal-stress", "target": "visual:thermal-restraint", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "topic:topic-thermal", "type": "Topic", "label": "Thermal management and heat transfer", "properties": { "id": "topic-thermal", "name": "Thermal management and heat transfer", "lede": "How heat is made, moved and removed in cells and packs, and the hardware that keeps a battery at the right temperature.", "context": "Select spatial detail for the question.", "example": "Equal total heat in different layouts can produce different gradients. Average temperature can miss a hot spot.", "lesson_url": "https://lemonergy.com/learn/fundamentals/battery-aging/", "lesson_label": "Open temperature and aging" } }, { "id": "term:thermal-expansion-coefficient", "type": "Term", "label": "Coefficient of thermal expansion", "properties": { "id": "thermal-expansion-coefficient", "name": "Coefficient of thermal expansion", "abbr": "CTE", "aka": [ "thermal expansion coefficient", "thermal expansion" ], "section": "topic-thermal", "definition": "The fractional change in length per kelvin of temperature change. Aluminium expands about 23 ppm/K, copper 17, steel 12 and most plastics several times more, so joined parts in a pack — busbars, welds, adhesive bonds, potting — are strained every time it heats and cools.", "unit": "K⁻¹", "related": [ "thermal-stress", "thermal-shock-test", "glass-transition-temperature", "busbar", "structural-adhesive" ], "url": "https://lemonergy.com/learn/glossary/thermal-expansion-coefficient/", "mentions": [ "potting-compound" ] } }, { "id": "term:thermal-shock-test", "type": "Term", "label": "Thermal shock and cycling test", "properties": { "id": "thermal-shock-test", "name": "Thermal shock and cycling test", "section": "topic-testing", "definition": "Moving a cell or pack rapidly between temperature extremes, typically −40 °C and +60 to +85 °C, for many cycles, to find seals, welds and housings that fail by differential expansion. It is in UN 38.3, R100 and most pack specifications.", "related": [ "transport-regulations", "un-r100-part-2", "vibration-test", "abuse-testing" ], "url": "https://lemonergy.com/learn/glossary/thermal-shock-test/", "mentions": [ "un-r100" ] } }, { "id": "term:glass-transition-temperature", "type": "Term", "label": "Glass transition temperature", "properties": { "id": "glass-transition-temperature", "name": "Glass transition temperature", "abbr": "Tg", "section": "topic-thermal", "definition": "The temperature at which an amorphous polymer turns from hard and glassy to soft and rubbery, with a sharp fall in stiffness and rise in expansion. Adhesives, potting compounds and circuit boards are chosen with Tg clear of the operating range — standard FR-4 board is about 130–140 °C — so their joints are not loaded differently in service.", "related": [ "thermal-expansion-coefficient", "structural-adhesive", "potting-compound", "thermal-stress" ], "url": "https://lemonergy.com/learn/glossary/glass-transition-temperature/", "mentions": [] } }, { "id": "term:structural-adhesive", "type": "Term", "label": "Structural adhesive", "properties": { "id": "structural-adhesive", "name": "Structural adhesive", "section": "topic-pack", "definition": "A load-bearing adhesive, usually epoxy, polyurethane or acrylic, that bonds cells to each other, to the tray or to the lid so the cell block becomes part of the structure. Cell-to-pack and cell-to-chassis designs rely on it, at the price of cells that are hard to replace or to separate for recycling.", "related": [ "cell-to-pack", "cell-to-chassis", "thermally-conductive-adhesive", "design-for-recycling", "dismantling", "potting-compound" ], "url": "https://lemonergy.com/learn/glossary/structural-adhesive/", "mentions": [] } }, { "id": "term:busbar", "type": "Term", "label": "Busbar", "properties": { "id": "busbar", "name": "Busbar", "section": "topic-pack", "definition": "A rigid copper or aluminium conductor that joins cell terminals into series and parallel groups, and modules into the pack. Its cross-section is sized for current and heating, and its joints — welded or bolted — are a classic source of resistance and failure.", "related": [ "series-parallel", "terminal", "laser-welding", "internal-resistance", "wire-bonding" ], "url": "https://lemonergy.com/learn/glossary/busbar/", "mentions": [] } }, { "id": "visual:thermal-restraint", "type": "Visual", "label": "Restraining expansion creates stress", "properties": { "title": "Restraining expansion creates stress", "summary": "A fully restrained linear elastic bar develops stress proportional to temperature change.", "readout": "A 50 K change gives 80.5 MPa in this ideal fully restrained model.", "formula": "|σ| = E α |ΔT| for full uniaxial restraint", "note": "Constant E and α, small strain, no yielding or relaxation. Heating creates compression and cooling tension in a fully restrained bar.", "software": { "status": "reference", "label": "Reference concept", "body": "This ideal elastic estimate explains the term. It does not assess joints, yielding, fatigue or certify a battery structure.", "href": "../chapter-1/" }, "html": "
Restrained stress magnitude
Restrained stress magnitudeTemperature-change magnitude (K) versus Stress magnitude (MPa). Elastic full-restraint estimate. Interpretation follows the graphs.0032.22064.44096.66012980Temperature-change magnitude (K)Stress magnitude (MPa)
Elastic full-restraint estimate
" } } ] }