Failure analysis of composite materials

Date：2022-03-09 13:45:00 Views：1136

Composite materials are materials with new properties composed of two or more materials with different properties through physical or chemical methods. Various materials learn from each other in performance and produce synergistic effect, so that the comprehensive performance of the composite is better than that of the raw materials to meet various requirements. The matrix materials of composites are divided into metal and non-metal. Aluminum, magnesium, copper, titanium and their alloys are commonly used in metal matrix. Non metallic substrates mainly include synthetic resin, rubber, ceramics, graphite, carbon, etc. Reinforcement materials mainly include glass fiber, carbon fiber, boron fiber, aramid fiber, silicon carbide fiber, asbestos fiber, whisker, metal wire and hard fine particles.

failure mode

Fracture, discoloration, failure, corrosion, insufficient mechanical properties, etc

Common means

NDT:

Radiographic testing technology (X-ray γ X-ray, neutron ray, etc.), industrial CT, Compton Backscatter Imaging (CST) technology, ultrasonic testing technology (penetration method, pulse reflection method, tandem method), infrared thermal wave testing technology, acoustic emission testing technology, eddy current testing technology, microwave testing technology, laser holographic testing technology, etc.

Composition analysis:

For X-ray fluorescence spectrum analysis (XRF), see component analysis in polymer material failure analysis.

Thermal analysis:

Gravimetric analysis (TG), differential scanning calorimetry (DSC), static thermomechanical analysis (TMA), dynamic thermomechanical analysis (DMTA), dynamic dielectric analysis (deta)

Destructive test:

Sample preparation and ion beam analysis (FIB)

In order to avoid failure, the following matters should be paid attention to in the molding process of composite materials

1. The interlaminar strength of carbon fiber composites is low and it is easy to produce delamination under the action of cutting force. Therefore, the axial force should be reduced by drilling or trimming. Drilling requires high speed and small feed. The speed of the machining center is generally 3000 ~ 6000r / min, and the feed rate reaches 0.01 ~ 0.04mm/r. The drill bit adopts three tips and two edges or two tips and two edges. The sharp tip can cut off the carbon fiber layer first, and the two edges play a role in repairing the hole wall. The drill bit inlaid with gold and steel is sharp and wear-resistant. The drilling of composite and titanium alloy interlayer is a difficult problem. Generally, the integral cemented carbide bit is used to drill according to the cutting parameters of drilling titanium alloy. It is drilled from the side of titanium alloy until it is drilled through. Lubricant is added during drilling to alleviate the burn of composite materials. Boeing has specially developed PCD combined bit for drilling interlayer.

2. The cutting effect of three new types of special milling cutters for machining integral cemented carbide composites is better. They all have some common characteristics: high rigidity, small spiral angle, or even 0 °. The specially designed herringbone blade can effectively reduce the axial cutting force of the machining center and reduce delamination, and its machining efficiency and effect are very good.

3. Composite chips are powdery, which is harmful to human health. High power vacuum cleaner should be used for dust collection, and water cooling can also effectively reduce dust pollution.

4. Carbon fiber composite components are generally large in size, complex in shape and structure, and high in hardness and strength. They are difficult to process materials. In the cutting process, the cutting force is large, and the cutting heat is not easy to spread out. In serious cases, it will scorch the resin or soften the resin, and the tool wear is serious. Therefore, the tool is the key to carbon fiber processing, and its cutting mechanism is closer to grinding rather than milling. Therefore, the cutting linear speed of the machining center is usually greater than 500m / min, and the high speed and small feed strategy is adopted. The cutting tools for edge cutting are generally solid carbide knurled milling cutter, electroplated diamond particle grinding wheel, diamond inlaid milling cutter and copper based diamond particle saw blade.