Thermal cracking mechanism and engineering response of single-piece fireproof glass

Introduction

As a key material for building exterior protection, the thermal cracking behavior of glass in fire directly affects the escape of personnel and the spread of fire. This article focuses on the thermal cracking mechanism of **single-piece fireproof glass (DFB)** and analyzes its fire-resistant nature.

1. The core driving force of thermal cracking: temperature difference stress

Research has confirmed (Xie, Keski-Rahkonen, etc.) that the fundamental cause of glass cracking is the critical thermal stress caused by **uneven heating:

Ordinary soda-lime glass: critical temperature difference is only **80~90℃

6mm tempered fireproof glass**: critical temperature difference **330~380℃

10mm tempered fireproof glass**: critical temperature difference **470~590℃

When the temperature difference between the exposed area (fired) and the shielded area (frame) of the glass exceeds the threshold in a fire, the tensile stress generated exceeds the tensile strength of the glass (usually 30~50MPa), which triggers the crack.

2. Key factors affecting cracking

| Edge processing quality | Mechanical polishing edge strength (78MPa) > rough grinding edge (56MPa), micro crack expansion strength attenuation 15%+ |

| Installation method | Point support stress concentration > frame installation; aluminum frame fire resistance > wooden frame |

| External intervention | Spray cooling will accelerate cracking when the glass temperature is > 250℃ |

| Glass type | Borosilicate glass (expansion coefficient 4×10⁻⁶/K) Thermal shock resistance Rolled soda-lime glass (9×10⁻⁶/K)

📌 Engineering warning: Fireproof glass design must reserve a safety factor K≥2.5 (refer to curtain wall specifications)

3. Technical breakthrough direction

1. Material upgrade

Borosilicate glass: low expansion + high softening point (800℃), the mainstream fire protection solution in Europe, and has broken through the bottleneck of mass production in China

Microcrystalline glass: zero expansion characteristics, temporarily limited to high-end special applications

2. Process control

Stress strengthening: surface compressive stress > 90MPa (national standard bottom line) can improve bending strength (formula: σ≈0.83σ tempering + 38)

Edge finishing: HF acid etching/mechanical polishing to reduce microcracks

3. Intelligent simulation application

Thermal-mechanical coupling simulation based on tools such as ANSYS can predict:

Stress distribution of different installation methods (see Figure 1)

Critical rupture time (error <10%)

Simulation confirms: The maximum tensile stress of framed glass is concentrated at the junction of the frame and shielding (31~32MPa)

IV. Engineering application suggestions

1. Carefully select glass type

Borosilicate monolithic fireproof glass (EN 12600/ANSI Z97.1 certification) is the first choice for high-end projects

Strictly control the discrete risk of soda-lime-silicon fireproof glass

2. Optimize installation design

Preferentially use a four-point support structure to reduce stress concentration

The shielding width needs to be verified by thermal simulation

3. Scenario protection

Avoid enabling the sprinkler system at high temperature (>250℃)

Conclusion

To understand the mechanism of thermal cracking, it is necessary to make breakthroughs in three dimensions: material nature (boron silicon > sodium calcium), process precision (edge ​​stress control), and installation science (thermal stress dispersion). With the large-scale mass production of domestic borosilicate glass and the popularization of digital simulation technology, the safety of fireproof glass will achieve a qualitative leap.