The uniformity of surface stress distribution in lighting tempered glass is a key indicator of its mechanical strength, impact resistance, and safety. In lighting applications, glass is often subjected to thermal cycling, mechanical vibration, and external impact. Uneven stress distribution can easily lead to localized stress concentrations, potentially posing a risk of cracking or spontaneous explosion. Therefore, scientific testing methods are necessary to assess uniformity and ensure product compliance with safety standards.
Polarimetric stress measurement is a fundamental method for testing the uniformity of surface stress distribution in lighting tempered glass. This method, based on the principle of birefringence, utilizes a polarized light field system to observe interference fringes caused by internal stress in the glass. During testing, the glass is placed in the polarized stress measurement instrument. The polarized light angle is adjusted by rotating the stage, allowing the light to pass through the glass to form an interference pattern. If the stress distribution is uniform, the interference fringes should exhibit a regular pattern of parallel or concentric circles. If the stress is uneven, the fringes will be distorted, fractured, or exhibit sudden changes in density. This method is simple to use and suitable for rapid on-site screening, but it relies on the tester's experience in determining fringe morphology and cannot provide quantitative data.
The photoelastic method, by constructing a polarized light field system and employing a helium-neon laser source with four-step phase shifting technology, can acquire full-field stress distribution data on lighting tempered glass. During testing, the laser penetrates the glass, causing a change in optical path length due to stress differences, resulting in interference fringes. By analyzing the phase differences within these fringes, the stress values at each point on the glass surface can be calculated and a three-dimensional stress map can be generated. This method has low measurement error and can accurately locate areas of stress concentration, but the equipment cost is relatively high, making it suitable for laboratories or for quality control of high-end lighting products.
X-ray diffraction analyzes stress distribution in lighting tempered glass by lattice strain. This method utilizes a radiation source to illuminate the glass surface and calculates stress values by measuring changes in lattice spacing. Equipped with a two-dimensional detector, it enables rapid scanning across a range of incident angles, minimizing single-point testing time. This method does not rely on the optical properties of the glass and is suitable for testing chemically tempered or coated glass. However, it requires destructive sampling and extremely high equipment precision. It is typically used in R&D or failure analysis.
The ultrasonic transit-time method, based on the theory of acoustic elasticity, estimates stress distribution by measuring the mathematical relationship between the propagation speeds of longitudinal and shear waves in glass and stress. During testing, a focused probe transmits ultrasonic waves into the glass, receives the reflected wave signals, and analyzes the changes in transit-time to calculate stress. This method enables non-contact measurement, avoids secondary damage to the glass, and is suitable for in-line testing of curved glass. However, it requires an accurate velocity-stress model and is sensitive to glass thickness uniformity, necessitating verification using other methods.
The laser speckle interferometry method assesses stress uniformity in lighting tempered glass by capturing changes in the microstrain field under dynamic loading. During testing, a pulsed laser illuminates the glass surface, and a high-speed CCD records the real-time changes in the speckle pattern. When the glass is subjected to stress and deformation, the speckle pattern shifts. Digital image correlation algorithms analyze the displacement field to derive the stress distribution. This method offers high displacement resolution and can monitor stress changes in real time, making it suitable for fatigue testing in environments that simulate lighting fixtures. However, the equipment is complex and requires specialized operators.
In actual testing, a comprehensive assessment of the stress uniformity of lighting tempered glass requires a combination of methods. For example, a preliminary screening is performed using a polarimetric stress meter, followed by quantitative analysis of suspected areas of stress nonuniformity using photoelasticity or X-ray diffraction, and finally, verification of overall uniformity using ultrasonic transit-time method. Furthermore, the testing environment must be strictly controlled for temperature, humidity, and vibration to avoid external interference. For example, the glass must be kept in a constant temperature environment before testing to eliminate the effects of temperature gradients on stress.
Testing the surface stress uniformity of lighting tempered glass requires the integration of multiple technical approaches, from qualitative screening to quantitative analysis, forming a comprehensive quality control system. Through scientific testing, the risk of breakage of lighting glass during use can be effectively reduced, product safety and reliability can be improved, and consumers can be provided with better lighting solutions.
