Prevention of Fatigue Failure in Jack Shock-Absorbing Rubber Blocks
Jack shock-absorbing rubber blocks play a critical role in cushioning, vibration reduction, and load distribution during lifting operations. Fatigue failure, caused by repeated cyclic loading, can compromise safety and reduce the service life of the rubber blocks. Understanding the causes and implementing preventive measures are essential for reliable performance.
1. Causes of Fatigue Failure
Repeated Load Cycling: Continuous lifting and lowering operations induce cyclic stress in the rubber, leading to microcracks and eventual fatigue failure.
Overloading: Applying loads beyond the design capacity increases stress amplitude and accelerates crack initiation.
Environmental Factors: High or low temperatures, UV exposure, ozone, and contact with oils or chemicals can degrade the rubber’s elasticity, making it more susceptible to fatigue.
Manufacturing Defects: Inhomogeneous material, improper vulcanization, or air inclusions can serve as stress concentrators, promoting early fatigue damage.
2. Material Selection
Choosing the appropriate rubber compound is fundamental to fatigue resistance:
Polyurethane: Excellent for high-load applications due to high tensile strength and resilience.
EPDM or NBR: Provide resistance to temperature extremes, ozone, and chemical exposure, preserving elasticity under cyclic loading.
Hardness Optimization: Selecting the correct Shore A hardness ensures balance between flexibility and load-bearing capacity, reducing stress concentrations.
3. Design Considerations
Load Distribution: Properly sized and shaped blocks distribute stress evenly, reducing localized fatigue.
Stress Relief Features: Rounded edges, uniform thickness, and smooth surfaces help minimize stress concentration points.
Bonding Quality: Secure adhesion or mechanical fixation prevents relative motion, which can create additional cyclic stress and wear.
4. Operational Guidelines
Avoid Overloading: Operate jacks within their rated capacity to prevent excessive cyclic stress.
Controlled Lifting and Lowering: Minimize sudden impacts and jerky motions that increase dynamic stress on rubber blocks.
Environmental Protection: Shield rubber blocks from UV, ozone, and chemical exposure to maintain elasticity and fatigue resistance.
5. Maintenance and Inspection
Regular Inspections: Look for early signs of surface cracking, bulging, hardening, or loss of elasticity.
Timely Replacement: Replace blocks showing fatigue damage before cracks propagate to prevent operational failure.
Storage Practices: Store spare blocks in cool, dry, and UV-protected environments to prevent premature degradation.
Conclusion
Fatigue failure in jack shock-absorbing rubber blocks can be prevented through careful material selection, proper design, load management, environmental protection, and routine maintenance. Implementing these measures enhances safety, prolongs service life, and ensures reliable performance.
References
Gent, A. N. Engineering with Rubber: How to Design Rubber Components. Hanser Publishers, 2012.
ASTM D573 – Standard Test Method for Rubber—Deterioration in an Air Oven.
Lake, G. J. “Fatigue and Fracture of Elastomers.” Rubber Chemistry and Technology, 2000.
ISO 2285 – Rubber Products — Determination of Tensile Stress-Strain Properties.
