Why do beryllium bronze springs fail?

The failure causes of beryllium bronze springs

l 1. Fatigue Failure

Fatigue failure is the most common failure form of beryllium bronze springs. During long-term use, after being subjected to repeated loads, the springs will develop cracks, deformations and other phenomena, resulting in failure.

l 2. Insufficient Strength

The insufficient strength of beryllium bronze springs is also one of the reasons for their failure. If the material strength of the springs is lower than the required strength, they are prone to plastic deformation when subjected to loads, affecting the performance and usage effect.

l 3. Surface Damage

Surface damage of beryllium bronze springs can also lead to their failure. Surface damage includes scratches, wear, corrosion, etc. These damages will affect the service life and performance of the springs.

Main types and causes of failure of beryllium bronze springs

l 1. Failure caused by material defects

Beryllium bronze (such as C17200) typically contains 1.8%-2.0% beryllium (in accordance with ASTM B196 standards). If during the smelting process there is component segregation or excessive impurities (such as lead > 0.005%), brittle phases will form, reducing the material's ductility. For example, a certain aviation relay spring suffered from intergranular cracks due to uneven beryllium distribution, and its service life was reduced to less than 50,000 cycles (the standard requires ≥ 100,000 cycles).

l 2. Processing issues

- Inadequate control of cold work hardening: During spring formation, the deformation amount should be controlled within 15%-20%. Excessive cold rolling will lead to concentrated residual stress, and if the subsequent aging treatment (at 300°C for 2 hours) has a temperature deviation of ±10°C, the hardness fluctuation can reach HRC 5 levels.

- Defects in heat treatment: Failure to fully solute (such as below 780°C) will result in residual β phases, reducing the elastic modulus (normal value ≥ 128 GPa).

Influence of Environment and Operating Conditions

l 1. Corrosion Failure

Beryllium bronze is prone to stress corrosion cracking (SCC) in environments containing sulfur or chloride ions. Experiments show that in an atmosphere with 50 ppm H₂S, the fracture time of the spring plate can be shortened to 72 hours (in accordance with ISO 9223 standard). Typical case: The contact resistance of a spring plate on an offshore equipment increased from 5 mΩ to 50 mΩ due to salt fog corrosion.

l 2. Fatigue Failure

Under high-frequency operation (e.g., 10 times per second), the spring plate is prone to crack at the stress concentration area (such as at the bending radius < 0.3mm). The fatigue life formula Δσ = σₐNᵇ (where σₐ is the stress amplitude and N is the number of cycles) indicates that when σₐ > 600 MPa, the lifespan drops below 1×10⁶ times (refer to the Manson-Coffin model).

Improvement Measures and Verification

l 1. Material Optimization

Use vacuum melting to reduce oxygen content (<30ppm), and add 0.1%-0.3% nickel to enhance corrosion resistance. A certain manufacturer's improved spring sheet passed the salt spray test for 480 hours (GB/T 10125-2021).

l 2. Process Control

- Introduce a laser thickness gauge to ensure cold rolling tolerance of ±0.01mm;

- Add hydrogen annealing process (200℃×4h) to eliminate the risk of hydrogen embrittlement.

l 3. Design Improvement

Finite element analysis shows that increasing the bending radius from 0.2mm to 0.5mm can reduce the stress concentration coefficient Kt from 3.2 to 1.8, and the fatigue life is increased by 3 times.