Why does leaf spring break easily?

Leaf springs are core load-bearing suspension components of heavy trucks and semi-trailers. Frequent breakage is rarely caused by single factor, but a combination of improper selection, overloaded operation, poor maintenance, inferior raw materials and defective production processes. Every root cause will create microcracks on steel plates, which expand continuously under cyclic vibration load and finally lead to sudden fracture during driving. The detailed main reasons are sorted as follows.

First, long-term overloading and excessive instantaneous impact load are the most common triggers of spring fracture. Each leaf spring assembly is designed with a fixed rated load corresponding to axle tonnage. When vehicles carry cargo beyond the spring’s bearing limit for a long time, the steel plate bears persistent excessive bending stress, resulting in irreversible flattening of spring arch. The internal metal structure produces tiny fatigue cracks. For mining dump trucks and sand haulage vehicles running on rugged mine roads, bumps, steep slopes and frequent heavy impact generate dynamic load 1.2 to 1.5 times static load, accelerating crack expansion sharply. Even high-quality alloy steel springs will break quickly under years of overload operation.

Second, mismatched leaf spring specifications fail to adapt to vehicle working conditions. Many users blindly replace springs without matching axle tonnage, leaf quantity and structural style. Installing thin 3-leaf light-load springs on 16-ton heavy axles leads to insufficient rigidity and concentrated stress on single steel sheets. Choosing soft parabolic springs for mine transport vehicles cannot resist frequent impact deformation. In addition, mismatched arch height, length or width will make springs squeeze against frame brackets, U-bolts and limit blocks during driving, forming local stress concentration points that crack easily after repeated friction and collision.

Third, inferior raw materials and incomplete heat treatment cut fatigue resistance drastically. Qualified heavy-duty leaf springs adopt 60Si2Mn or 50CrV4 alloy spring steel. Cheap counterfeit products use ordinary carbon steel with low elastic limit and poor toughness, which crack after short service cycles. Even with qualified alloy steel, incomplete manufacturing processes will damage performance. Springs without full quenching and tempering treatment cannot form stable elastic structure; those skipping shot peening lack surface compressive stress layer, so surface microcracks expand rapidly under vibration. Uneven steel thickness and rough cutting edges also become natural crack sources.

Fourth, improper installation and damaged supporting accessories induce abnormal stress on leaf springs. Loose U-bolts are a typical installation fault. If U-bolts are not tightened evenly, springs shift left and right during driving, generating shear force and tearing spring eyes. Worn, aging rubber bushings lead to metal-to-metal friction between spring eyes and shackles, creating impact cracks at the root of main leaf. Asymmetric spring assembly, uneven left-right chassis height and deformed balance beams of bogie suspension will cause unilateral overloading of one spring group, leading to premature fracture on one side. Missing inter-leaf wear gaskets also aggravate mutual abrasion between steel plates and thin the main leaf rapidly.

Fifth, lack of daily maintenance and long-term corrosion damage steel structure. Mud, rainwater, road salt and mine mineral wastewater erode uncoated spring surfaces, producing rust pits. Rust pits act as stress concentration points, greatly reducing anti-fatigue performance. Most fleet operators ignore regular cleaning and lubrication of leaf springs. Without periodic rust prevention treatment and lubrication between leaves, abrasion and corrosion accumulate year by year. Besides, long-term partial cargo load causes permanent unilateral deformation of springs, and small cracks cannot be detected in time during routine inspection, evolving into complete fracture during transportation.

Sixth, driving habits aggravate spring damage. Fierce full-load startup, emergency braking and high-speed crossing of pits and speed bumps bring instantaneous strong impact to suspension. Continuous low-speed climbing under full load keeps springs under maximum bending stress for a long time, accelerating metal fatigue. These improper operations will shorten the service life of leaf springs by more than half compared with standardized driving habits.

To sum up, the primary causes for easy breakage of leaf springs include long-term overload impact, mismatched spring specifications, low-grade raw materials and incomplete heat treatment, incorrect installation and damaged auxiliary parts, corrosion due to insufficient maintenance, and aggressive driving behaviors. To effectively avoid frequent spring breakage, users should select springs matched to axle tonnage and working conditions, control cargo weight within rated load, standardize installation procedures, regularly maintain anti-rust and lubrication work, and develop gentle driving habits.

1. APA 7th Edition

Zhang, L. (2026). Failure cause analysis and preventive measures of easy fracture on commercial vehicle leaf springs. Vehicle Chassis Fault Diagnosis Technology, 2(1), 81–88.

2. MLA 9th Edition

Zhang, Lei. "Failure Cause Analysis and Preventive Measures of Easy Fracture on Commercial Vehicle Leaf Springs." Vehicle Chassis Fault Diagnosis Technology, vol. 2, no. 1, 2026, pp. 81–88.

3. GBT 7714-2015

Zhang Lei. Cause analysis and preventive measures for the failure of leaf springs in commercial vehicles [J]. Vehicle chassis fault diagnosis technology, 2026, 2 (1): 81-88.