What are the common causes of leaf spring fractures?

Leaf spring fracture is a frequent suspension failure in trucks, trailers and heavy machinery. It is mainly induced by excessive alternating stress, surface defects, improper maintenance, wrong operation and material damage. The detailed common causes are sorted as follows:

1. Overloading and uneven cargo distribution (primary inducement)

Long-term overload far exceeding the vehicle rated load sharply raises bending stress of spring plates, producing continuous high alternating fatigue load. Microcracks form and expand rapidly until fracture.

Unbalanced loading: concentrated cargo on one side or front/rear creates unilateral overload, leading to asymmetric torsion and shear stress on the leaf spring assembly. Local stress concentration triggers cracks at spring roots.

Long-term heavy partial load makes single-side springs bear persistent extra load, accelerating fatigue aging and early breakage.

2. Severe impact load from improper driving behavior

High-speed crossing of potholes, speed bumps and rough roads generates instantaneous shock overload, creating instant peak stress that initiates surface microcracks.

Frequent emergency braking, sharp acceleration and sharp turns produce huge lateral and longitudinal shear force, distorting spring leaves and causing stress concentration at clamping positions.

Downhill heavy braking causes weight transfer, imposing extra compressive and bending load on front or rear leaf springs.

High-speed empty vehicle driving leads to violent suspension bouncing; repeated up-and-down vibration brings high-frequency fatigue damage to thin spring plates.

3. Loose or damaged fasteners leading to abnormal friction

Loose U-bolts form gaps between stacked spring leaves. Relative sliding friction under vibration wears leaf surfaces and produces stress notches, which become crack sources.

Broken or loose center bolts cause lateral displacement of spring plates, uneven force bearing and local overload fracture.

Worn, aging or cracked shackle/hanger rubber bushings change the spring swing track, introducing additional torsion stress and abnormal friction between leaves.

4. Lack of lubrication and severe corrosion damage

No regular greasing between spring leaves: dry metal friction generates high temperature and abrasion scratches on leaf surfaces. These scratches expand into fatigue cracks under cyclic load.

Mud, gravel, road salt and sewage accumulate between leaves. Corrosion pits form on steel surfaces; pits act as stress concentration points and greatly reduce fatigue resistance.

Chassis anti-rust coating peeling without timely repair leads to rust penetration, thinning spring cross-section and brittle fracture under load.

5. Foreign particle clamping and surface scratch defects

Stones, metal scraps and hard debris trapped between spring leaves scratch leaf surfaces during compression and rebound. Surface indentations and scratches are vulnerable positions for crack propagation.

Original manufacturing defects: rolling scratches, quenching cracks and oxide layers on spring raw materials develop into fractures after long service.

6. Damaged matching auxiliary parts

Failed, leaking shock absorbers cannot restrain suspension bouncing. High-frequency reciprocating vibration intensifies alternating stress and accelerates leaf spring fatigue fracture.

Missing or damaged limiting blocks cause over-compression of leaf springs under heavy load, resulting in direct hard collision and instant breakage of spring plates.

Unbalanced axles produce periodic vibration during driving, continuously impacting leaf springs and aggravating fatigue wear.

7. Improper heating, welding and unauthorized modification

Random welding, cutting or local heating on leaf springs destroys the original quenching-tempered metallographic structure. The spring loses toughness, becomes brittle and fractures easily under small impact.

Private modification such as cutting spring leaves, adding unqualified auxiliary springs changes the original stress design, causing abnormal local stress concentration.

8. Permanent plastic deformation and fatigue aging

Long-term overload leads to irreversible sagging deformation of leaf springs. The camber deviates from the design value, and stress distribution becomes chaotic. Deformed springs bear excessive local load and crack quickly.

Long service cycle: cumulative fatigue damage forms invisible internal microcracks, which suddenly expand into complete fracture under sudden impact or heavy load.

Summary

Almost all leaf spring fractures originate from stress concentration points on spring plates, including surface scratches, corrosion pits, friction notches and structural distortion. Overload, impact and loose fasteners continuously amplify alternating fatigue stress, eventually causing crack initiation and full fracture.

References

APA 7th Edition

Kong, Y. S., Omar, M. Z., & Chua, L. B. (2014). Fatigue life prediction of parabolic leaf spring under various road conditions. Engineering Failure Analysis, 46, 92–103. 

MLA 9th Edition

Kong, Y. S., et al. "Fatigue Life Prediction of Parabolic Leaf Spring under Various Road Conditions." Engineering Failure Analysis, vol. 46, 2014, pp. 92–103, 

GB/T 7714-2015

KONG Y S, OMAR M Z, CHUA L B. Fatigue life prediction of parabolic leaf spring under various road conditions[J]. Engineering Failure Analysis, 2014, 46:92-103.