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Fatigue01:21

Fatigue

Fatigue occurs when materials rupture under repeated or fluctuating loads, even at stress levels far below their static breaking strength. It typically results in brittle failure, even for ductile materials. It is a critical consideration in designing machines and structural components subjected to repetitive or varying loads. The nature of these loadings can range from fluctuating loads like unbalanced pump impellers causing vibrations to repeatedly bending a thin steel rod wire back and forth...
Impact Loading01:19

Impact Loading

Impact loading occurs when a moving object collides with a stationary structure, such as a rod with a uniform cross-sectional area fixed at one end. Under these conditions, the rod absorbs the kinetic energy from the striking object, leading to deformation and subsequent stress development. As the rod returns to its original position and reaches maximum stress, the absorbed energy, initially manifested as kinetic energy, transforms entirely into strain energy.
In cases of elastic deformation,...
Stresses under Combined Loadings01:23

Stresses under Combined Loadings

When analyzing a bent tube with a circular cross-section subjected to multiple forces, it is crucial to determine the stress distribution in order to maintain structural integrity under varied load conditions.
The process begins by slicing the tube at critical points and analyzing the internal forces and stress components at these sections, focusing on the centroid. Normal stresses, generated by axial forces and bending moments, are either compressive or tensile and vary across the section from...
Stress-Strain Diagram - Ductile Materials01:24

Stress-Strain Diagram - Ductile Materials

The stress-strain relationship in ductile materials such as structural steel or aluminium is intricate and progresses through several stages. When a specimen is loaded, it initially exhibits a linear length increase, depicted by a steep straight line on the stress-strain diagram. It indicates the material is elastically deforming and will return to its original shape once unloaded. However, when a critical stress value is reached, plastic deformation begins. This stage sees substantial...
Normal Strain under Axial Loading01:20

Normal Strain under Axial Loading

Normal strain under axial loading is an important concept in the field of mechanics of materials. Axial loading implies the application of a force along the axis of a material, like a column or bar. This force can either compress or stretch the material. In the context of axial loading, normal strain is the deformation experienced by the material in the direction of the loading force. It's calculated as the change in length divided by the original length of the material. This unitless ratio...
Residual Stresses in Bending01:18

Residual Stresses in Bending

In the study of elastoplastic members subjected to bending moments, understanding the loading and unloading phases is crucial for assessing material behavior and structural integrity. During the loading phase, as the bending moment increases, the material initially responds elastically, adhering to Hooke's Law, where stress is directly proportional to strain. When the load exceeds the yield strength, plastic deformation occurs, resulting in permanent strain and deformation that remains even...

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Related Experiment Video

Updated: May 17, 2026

A Coupled Experiment-finite Element Modeling Methodology for Assessing High Strain Rate Mechanical Response of Soft Biomaterials
11:28

A Coupled Experiment-finite Element Modeling Methodology for Assessing High Strain Rate Mechanical Response of Soft Biomaterials

Published on: May 18, 2015

Simulation of cumulative damage associated with long term cyclic loading using a multi-level strain accommodating

Moustafa Nabil Aboushelib1

  • 1Dental Biomaterials Department, Faculty of Dentistry, Alexandria University, Alexandria, Egypt. info@aboushelib.org

Dental Materials : Official Publication of the Academy of Dental Materials
|November 13, 2012
PubMed
Summary

This study tested how zirconia veneered dental crowns hold up under long-term simulated chewing forces. Using a new loading protocol that mimics the damping effects of the periodontal ligament and jaw movement, researchers applied 3.5 million cycles of stress to 40 crowns. Most survived without breaking, and those that did fail showed specific patterns of microcrack growth. The findings suggest that these crowns can last many years in the mouth, provided they are made without defects. The study used a detailed method to track how cracks form and spread, offering insight into how to improve the durability of dental restorations.

Keywords:
dental restorationscyclic loadingfractographic analysiszirconia crowns

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Area of Science:

  • Dental materials science
  • Biomechanics in restorative dentistry

Background:

Zirconia-based dental restorations are widely used for their strength and aesthetics. However, long-term performance under cyclic loading remains uncertain. Prior research has shown that these restorations can fail due to microcracks and wear. The mechanisms behind such failures are not fully understood. No prior work had resolved how clinical conditions like jaw movement and food texture affect damage accumulation. This gap motivated the development of a new loading protocol. The protocol aims to simulate realistic oral conditions. It incorporates damping effects from the periodontal ligament and jaw motion. This study builds on existing knowledge to better predict clinical outcomes.

Purpose Of The Study:

The study aimed to evaluate cumulative damage in zirconia veneered crowns under simulated long-term cyclic loading. The researchers wanted to understand how repeated stress affects structural integrity. They focused on the role of strain damping in preventing fractures. The study used a new loading protocol to mimic clinical conditions. This protocol included damping from the periodontal ligament and jaw movement. The goal was to reproduce realistic failure patterns. The researchers also aimed to assess how microcracks develop over time. Their findings could improve the design of dental restorations.

Main Methods:

Forty zirconia veneered crowns were tested using a multi-level strain accommodating loading protocol. The protocol simulated the damping effects of the periodontal ligament and jaw movement. Each specimen underwent 3.5 million cycles at a maximum load of 25 kg. The load speed was based on adult chewing cycles. Fractographic analysis was used to examine crack origins and damage progression. The loading setup allowed for free mandibular joint movement. Researchers tracked microcrack formation and crack propagation paths. The method aimed to replicate clinical failure mechanisms.

Main Results:

Twenty-nine of forty specimens (73%) survived 3.5 million cycles without fracture. Nine specimens (22%) showed cohesive fracture of the veneer ceramic. Two specimens (5%) had limited axial framework fractures. Two restorations (5%) failed after 500,000 cycles. The remaining fractures occurred after 3 million cycles. Fractographic analysis revealed initial wear and abrasion below the loading area. Subsurface microcracking of the glass matrix was observed. Crack growth followed a stepping pattern until deflection at the zirconia-veneer interface. The protocol prevented cone cracks and contact damage seen in standard fracture tests.

Conclusions:

The multi-level strain accommodating loading protocol successfully simulated clinical failure in zirconia veneered restorations. The study showed that these restorations can survive a simulated 7-year service time. Manufacturing errors were the only cause of early failure. The findings suggest that strain damping reduces crack formation. The stepping crack growth pattern was consistent across fractured specimens. The protocol mimicked the damping effects of the periodontal ligament and jaw movement. The results support the use of this method for evaluating long-term durability. The study did not propose new design changes or future research directions.

The protocol prevented cone cracks and contact damage, simulating clinical failure in zirconia veneered restorations.

It incorporates damping from the periodontal ligament, jaw deformation, and mandibular joint movement.

It helps identify the origin and progression of microcracks leading to structural failure in the veneer ceramic.

Subsurface microcracks in the glass matrix grow in a stepping pattern, eventually causing fracture at the veneer interface.

Twenty-nine specimens (73%) survived 3.5 million cycles without fracture.

The study suggests these restorations can survive a simulated 7-year service time without fracture, except for manufacturing errors.