Fernández Pelayo

Stress relaxation behaviors of articular cartilages in porcine temporomandibular joint

In this study, we tested the compressive stress relaxation behaviors of the mandibular condylar and temporal cartilages in the porcine temporomandibular joint (TMJ). The aim was to determine the quantitative and qualitative similarities and differences of compressive stress relaxation behaviors between the two cartilages. Ten porcine TMJs were used; the articular surface was divided into 5 regions: anterior, central, posterior, lateral and medial. Compressive relaxation test was carried out at a strain level of 5% in each region of the two cartilages. The stress relaxation was monitored over a period of 5min. In all the regions of the two cartilages, the time-dependent stress relaxation curves showed a marked drop in stress within the initial 10s, which can be fitted by a standard linear viscoelastic model. The instantaneous moduli in the temporal cartilage were dominantly larger than those in the condylar cartilage, while the condylar cartilage had slightly larger relaxation moduli than the temporal cartilage except for the medial region. The both cartilages showed the regional differences in the compressive stress relaxation behavior, and in the temporal cartilage the lateral and medial regions revealed the largest values for the instantaneous and relaxation moduli. The present results demonstrate that the viscoelastic properties of compressive stress relaxation in both cartilages are region-specific, which might have an important implication for stress distribution and transmission along with the TMJ disc.

Dynamic and stress relaxation properties of the whole porcine temporomandibular joint disc under compression.

In this study, the dynamic and static compressive properties of the whole porcine temporomandibular joint (TMJ) disc were investigated. The aim of the study was to develop a new simple method for the evaluation of joint viscoelasticity, enabling examination of the load-bearing capacity and joint flexibility of the entire disc. For the experiments, a novel testing fixture that reproduces the condylar and fossa surfaces of the TMJ was developed to replicate TMJ disc geometry. Ten porcine discs were used in the experiments. Each disc was dissected from the TMJ and sinusoidal compressive strain was applied to obtain the storage and loss moduli. Static strain control tests were carried out to obtain the relaxation modulus. The result of static and dynamic tests indicated that the whole disc presented viscoelastic behavior under compression. Storage and loss moduli increased with frequency and the relaxation modulus decreased over time. The loss tangent showed less frequency dependence, with values ranging from 0.2 to 0.3, suggesting that the viscous properties of the disc cannot be neglected. These results provide a better understanding of whole disc mechanical compression behavior under realistic TMJ working conditions.

Fatigue damage detection and prediction of fatigue life on a cantilever beam

Purpose Fatigue failure is an important criterion to be considered in the design of structures and mechanical components. Catastrophic failure of structures in service conditions can be avoided using adequate techniques to detect and localize fatigue damage. Modal analysis is a tool used in mechanical and structural engineering to estimate dynamic properties and also to monitor the health of structures. If modal analysis is applied periodically to a structure, fatigue damage can be detected and localized and the fatigue life can be extended by means of suitable reinforcement and repairing. The paper aims to discuss these issues. Design/methodology/approach The experimental results corresponding to the fatigue tests carried out on a steel S-275 cantilever beam are presented. Operational modal analysis was applied periodically to the beam in order to study the variation of modal parameters during the tests and the stresses were estimated combining a numerical model and the acceleration modal coordinates measured at discrete points of the structure. The experimental results are compared with those predicted applying the S-N model of Eurocode 3. Findings A methodology that combines a finite element model and the experimental responses of a structure has been applied to estimate the stress time histories of a cantilever beam clamped to a foundation through a steel plate. The estimated stresses have been used to predict the fatigue damage according to the Eurocode 3. Due to the fact that no information of the scatter is provided by this code (EC3), only the number of cycles corresponding to a probability of failure of 5 percent can be predicted. Originality/value The proposed methodology can be applied to real structures in order to know the accumulated fatigue damage in real time.

Evaluation of Conventional Al 2024 Fatigue Limit in Fatigue Test Using Thermographic Measurement: Effect of Frequency

The reliability of the conventional fatigue limit estimation of aluminum alloy Al 2024 provided by thermographic measurements according to the Risitano method is investigated in order to check their validity for practical applications. With this aim, an experimental fatigue program on Al 2024 specimens under load control using a stress ratio R = 0.1 is performed at three different frequencies. The fatigue limit methodologies is first determined according to the methodologies proposed by Risitano et al. and Canteli et al., and then compared with that resulting from the conventional Wöhler curve.

Thermographic Determination Methodology: Application on Fatigue Limit of AL 2024 for R=-1

The application of infrared thermography to obtain the external surface temperature during the application of cyclic loading, allows to evaluate the dynamic behavior of an element and to determine the fatigue limit. In this contribution, the reliability of the fatigue limit provided by the Risitano et al. and Canteli et al. methodologies is investigated in order to check their validity for practical applications. With this aim, an experimental program on aluminium specimens (AL 2024) under load control using a stress ratio minus one is performed. The fatigue limit for AL 2024 is derived, first from the Wöhler curve and then, compared with both Risitano et al. and Canteli et al. methodologies.

Analysis of Compressive Properties of Porcine Temporomandibular Joint Disc

Since the temporomandibular joint (TMJ) disc material exhibits a non-homogenous and viscoelastic structure, the compressive properties in five different regions of eleven porcine TMJ discs were investigated over a wide range of loading frequencies. The results obtained suggest that the dynamic viscoelastic compressive modulus is region-specific and depends on the loading frequency, thus having important implications for the transmission of load in the TMJ. The dynamic storage and loss moduli increase with frequency, the highest values being attained at the posterior region, followed by the central and anterior regions. Loss tangent, tan δ, ranged from 0.20 to 0.35, which means that the disc is primarily elastic in nature and has a small but not negligible viscosity.