{
  "node": {
    "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": []
    }
  },
  "edges": [
    {
      "id": "edge:4656",
      "source": "term:glass-transition-temperature",
      "target": "topic:topic-thermal",
      "type": "belongsTo",
      "properties": {
        "sourceFile": "terms.json"
      }
    },
    {
      "id": "edge:4657",
      "source": "term:glass-transition-temperature",
      "target": "term:thermal-expansion-coefficient",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:4658",
      "source": "term:glass-transition-temperature",
      "target": "term:structural-adhesive",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:4659",
      "source": "term:glass-transition-temperature",
      "target": "term:potting-compound",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:4660",
      "source": "term:glass-transition-temperature",
      "target": "term:thermal-stress",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    }
  ],
  "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: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:potting-compound",
      "type": "Term",
      "label": "Potting compound",
      "properties": {
        "id": "potting-compound",
        "name": "Potting compound",
        "aka": [
          "potting",
          "encapsulant"
        ],
        "section": "topic-pack",
        "definition": "A liquid resin — polyurethane, silicone or epoxy, sometimes foamed — poured around cells or electronics and cured into a solid block. It fixes cells against vibration, insulates them and can slow thermal propagation; some structural packs fill every gap between cylindrical cells with it. The cost is mass and a pack that is hard to repair or recycle.",
        "related": [
          "structural-adhesive",
          "thermal-propagation",
          "design-for-recycling",
          "dismantling",
          "vibration-test"
        ],
        "url": "https://lemonergy.com/learn/glossary/potting-compound/",
        "mentions": []
      }
    },
    {
      "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": []
      }
    }
  ]
}