Magnitude Of Peak Stress Research Articles

Dynamic compressive behavior of functionally graded triply periodic minimal surface cellular structures

The Triply Periodic Minimal Surface (TPMS) structure is regarded as a porous structure used for impact protection due to its lightweight, high strength, and high specific energy absorption (SEA). This paper investigates the dynamic mechanical properties of the TPMS structure by Split Hopkinson Bar (SHPB) experiments and finite element analysis (FEA). We compare stress peak, SEA, strain rate effect, and deformation pattern for functionally graded Primitive (P), uniform P, and uniform Gyroid (G) structures. It is found that the increasing magnitude of peak stress in the TPMS structures becomes more evident under high-impact loads. As the relative density increases, the strain rate effect becomes more prominent. The uniform G structures exhibit higher plateau stress and SEA than uniform P structures. Besides, graded P structures exhibit a climbing phenomenon compared to uniform P structures in the platform section. The FEA results also demonstrate that higher SEA and plateau stresses are exhibited in the graded P structure. The graded design minimizes the strain rate effect compared to the corresponding uniform structures. It is essential to set a properly graded index to enhance the dynamic energy absorption capacity of the TPMS structure, as more fluctuations occur when the graded index increases.

Frequency Spectra Analysis of Vertical Stress in Ballasted Track Foundations: Influence of Train Configuration and Subgrade Depth

Railway tracks experience stress during train passage. Understanding these subgrade stresses is essential for the design of track foundations and assessing their serviceability. However, few studies have explored the theoretical aspects of stress response in relation to train configuration. Therefore, this paper introduces a subgrade stress model for ballasted tracks, aiming to analyze the stress fields in track foundations under train loading. The model employs a unit impulse approach to represent the periodic axle sequence of a train moving at constant speed. It characterizes vertical stress transmission within geotechnical media using stochastic diffusion theory. With train configuration, track structure, and soil properties as inputs, the model can reconstruct the quasi-static time history and frequency spectrum of vertical subgrade stress at various depths. Frequency analysis indicates that as the number of axles increases, the dominant stress frequencies first align with integer multiples of the “bogie-passage frequency” and subsequently with integer multiples of the “vehicle-passage frequency.” Zero magnitudes may appear at dominant frequencies, depending on a vehicle's length and wheelbase. Peak stress magnitudes rapidly diminish at higher frequencies, with this attenuation becoming more pronounced as subgrade depth increases. The proposed model accounts for the structural features of trains and tracks, as well as the material properties of subgrade fills. It elucidates the mechanisms driving the quasi-static response of the subgrade when subjected to passing trains.

Crack initiation mechanisms in Ti-6Al-4V subjected to cold dwell-fatigue, low-cycle fatigue and high-cycle fatigue loadings

Although Ti-6Al-4V is the most commonly used titanium alloy in the aerospace industry, the mechanisms governing crack initiation in the different fatigue regimes are not well understood yet. This situation partly pertains to a competition between multiple crack initiation mechanisms. In particular, applied loading conditions were identified as a key parameter governing the transition between mechanisms. The fatigue behavior of Ti-6Al-4V with a bi-modal microstructure was investigated in the present study using different waveforms, load ratios and frequencies to clarify this feature. A detailed characterization of the main crack initiation sites was carried out to identify microstructural configurations governing crack nucleation in low-cycle dwell-fatigue, low-cycle fatigue and high-cycle fatigue regimes. While lifetimes and fracture surfaces showed a good consistency with data from prior studies, a single microstructural configuration was found involved with the formation of crack initiation facets. All investigated cracks leading to specimen failure were nucleated along (0001) twist grain boundaries exhibiting similar features. Based on this finding, a criterion is proposed to identify candidates for crack initiation. This also demonstrates no major sensitivity of the critical microstructural configurations to environment, free surface, loading conditions and, as shown in previous studies, microstructure and composition. However, conventional fatigue failure results from one, or a few, surface or subsurface crack initiation sites while dwell-fatigue failure involves the formation of multiple internal cracks. This is accompanied by a significant dwell-fatigue life debit at peak stress magnitudes close to the yield strength. Features of microstructural configurations prone to crack nucleation are finally compared with data reported in existing literature to propose a mechanism of crack formation in Ti alloys.

Structural response of monoblock railway concrete sleepers and fastening systems subject to coupling vertical and lateral loads: A numerical study

Monoblock prestressed concrete sleepers are the most dominant type of sleepers in ballasted railway tracks. As such, it is important to provide optimized designs to the concrete sleepers and the associated fastening systems to ameliorate railway safety and to save both capital and maintenance funds. Therefore, a three-dimensional finite element railway model was created and verified. The response of both concrete sleepers and fastening components to coupling vertical and lateral loading was quantified. Such loading form typically occurs at horizontal railway sections causing damage to the railway track components. The influences of the sleeper spacing, elastic modulus of the rail pad, and friction coefficient at the contact surfaces of the rail and sleeper with the rail pad under varied lateral loadings were investigated. The interaction influence between parameters was thoroughly discussed. Among the studied parameters, the finite element model outcomes showed that the elastic modulus of the rail pad and the coefficient of friction are the most critical parameters with respect to the lateral load path and the local response of concrete sleeper and fastening system, especially at high lateral loadings. By using a relatively soft rail pad (elastic modulus = 100 MPa), the concrete material remained below the compressive and tensile fatigue limits even under high lateral loadings provided that the coefficient of friction remains limited to 0.3. By contrast, for a given lateral to vertical loading ratio, a continuous increase in the developed stresses of the concrete material and rail pad was detected as the elastic modulus changed from 100 MPa to 2000 MPa and the coefficient of friction increased from 0.3 to 0.9. The influence of sleeper spacing on the behaviour of railway tracks is only tangible on the distribution of the vertical wheel load. Lastly, the peak stress magnitudes of the ballast bed could be increased by 50% as the lateral to vertical loading ratio reached 0.6 compared to the case where the lateral load is absent. The experience gained from this article would help to formulate specific recommendations to improve the design of concrete sleepers, fastening systems, and ballast bed.

Evaluation of various design concepts in passive ankle-foot orthoses using finite element analysis

Ankle-foot orthoses (AFOs) are typically prescribed to improve the gait function of ambulatory children with neurological conditions such as cerebral palsy or spina bifida. Due to the excessive and repetitive loading conditions, plastic material deformation can be observed in AFOs, especially over the lateral and medial parts of the ankle, which limits the effect of AFOs in the stabilization of the ankle joint. Trimline design and severity influence the rotational stiffness of an AFO considerably. In this study, we proposed novel trimming approaches for AFOs such that the trimlines were performed on the dorsal side rather than lateral and medial sides to reduce the magnitude of peak stresses and provide a homogenous stress distribution over AFOs. We analyzed eight dorsal trimline designs having different basic geometries by using the finite element method. To objectively evaluate the stress levels, the same boundary and loading conditions were considered for all design alternatives. We found that low peak stress values were observed in the AFO models with trimline geometries of the circle, ellipse, and slot variations. The vertical elliptic trimline on the dorsal side of the AFO was the most effective to decrease the magnitude of the peak stresses. The findings of our study are expected to contribute a complementary solution to orthotists in the fabrication of AFOs with high durability.

Individual variation in Achilles tendon morphology and geometry changes susceptibility to injury.

The unique structure of the Achilles tendon, combining three smaller sub-tendons, enhances movement efficiency by allowing individual control from connected muscles. This requires compliant interfaces between sub-tendons, but compliance decreases with age and may account for increased injury frequency. Current understanding of sub-tendon sliding and its role in the whole Achilles tendon function is limited. Here we show changing the degree of sliding greatly affects the tendon mechanical behaviour. Our in vitro testing discovered distinct sub-tendon mechanical properties in keeping with their mechanical demands. In silico study based on measured properties, subject-specific tendon geometry, and modified sliding capacity demonstrated age-related displacement reduction similar to our in vivo ultrasonography measurements. Peak stress magnitude and distribution within the whole Achilles tendon are affected by individual tendon geometries, the sliding capacity between sub-tendons, and different muscle loading conditions. These results suggest clinical possibilities to identify patients at risk and design personalised rehabilitation protocols.

Biomechanics of external fixator of distal radius fracture, a new approach: Mutifix Wrist

The purpose of this study was to assess factors affecting fixator stiffness with a finite element model and an experimental validation with particular attention to a new fixator device named Mutifix Wrist® (NCS Lab srl, Carpi, MO, Italy). Mechanical tests were carried out to determine the stiffness of the construct with different configurations. The obtained results were compared to those obtained with the Hoffmann II Compact (Howmedica-Osteonics Inc. Rutherford, NJ, USA). Data were sampled at 20Hz and test speed was 0.05mm/s. For each loading condition, tests were performed four times. A FEM campaign was also conducted to analyze how geometrical variables (type of configuration and K-wire diameter) affect both stiffness and stress distribution of the fixator. Stiffness, axial displacement, magnitude of the displacement, magnitude and localization of the peak stress of the construct were all analyzed. Axial compression tests showed that the axial displacement reached by the machine actuator when the measured force reached 45N was 0.56mm ± 0.13 on average. Magnitude of the displacement along with peak stress magnitude and localization varied through the several configuration tested, but it resulted that the distal pin near the fracture gap was the more stressed one in all cases except those in which the fracture line is crossed. From the tests performed, it emerged that the addiction of a K-wire provides a construct stiffening and a consequent local stress reduction; while span increase reduces stiffness and increase the local stress. If a K-wire is implanted through the fracture site, the axial stiffness is significantly increased.

A Combined Geometric Morphometric and Discrete Element Modeling Approach for Hip Cartilage Contact Mechanics

Finite element analysis (FEA) provides the current reference standard for numerical simulation of hip cartilage contact mechanics. Unfortunately, the development of subject-specific FEA models is a laborious process. Owed to its simplicity, Discrete Element Analysis (DEA) provides an attractive alternative to FEA. Advancements in computational morphometrics, specifically statistical shape modeling (SSM), provide the opportunity to predict cartilage anatomy without image segmentation, which could be integrated with DEA to provide an efficient platform to predict cartilage contact stresses in large populations. The objective of this study was, first, to validate linear and non-linear DEA against a previously validated FEA model and, second, to present and evaluate the applicability of a novel population-averaged cartilage geometry prediction method against previously used methods to estimate cartilage anatomy. The population-averaged method is based on average cartilage thickness maps and therefore allows for a more accurate and individualized cartilage geometry estimation when combined with SSM. The root mean squared error of the population-averaged cartilage geometry predicted by SSM as compared to the manually segmented cartilage geometry was 0.31 ± 0.08 mm. Identical boundary and loading conditions were applied to the DEA and FEA models. Predicted DEA stress distribution patterns and magnitude of peak stresses were in better agreement with FEA for the novel cartilage anatomy prediction method as compared to commonly used parametric methods based on the estimation of acetabular and femoral head radius. Still, contact stress was overestimated and contact area was underestimated for all cartilage anatomy prediction methods. Linear and non-linear DEA methods differed mainly in peak stress results with the non-linear definition being more sensitive to detection of high peak stresses. In conclusion, DEA in combination with the novel population-averaged cartilage anatomy prediction method provided accurate predictions while offering an efficient platform to conduct population-wide analyses of hip contact mechanics.

Design of plate and screw anchors in dense sand: failure mechanism, capacity and deformation

Plate and screw anchors provide a significant uplift capacity and have multiple applications in both onshore and offshore geotechnical engineering. Uplift design methods are mostly based on semi-empirical approaches assuming a failure mechanism, a normal and a shear stress distribution at failure and empirical factors back-calculated against experimental data. However, these design methods are shown to under- or overpredict most of the existing larger scale experimental tests. Numerical FE simulations are undertaken to provide new insight into the failure mechanism and stress distribution which should be considered in anchor design in dense sand. Results show that a conical shallow wedge whose inclination to the vertical direction is equal to the dilation angle is a good approximation of the failure mechanism in sand. This shallow mechanism has been observed in each case for relative embedment ratios (depth/diameter) ranging from 1 to 9. However, the stress distribution varies non-linearly with depth, due to the soil deformability and progressive failure. A sharp peak of normal and shear stress can be identified close to the anchor edge, before a gradual decrease with increasing distance along the shear plane. The peak stress magnitude increases almost linearly with embedment depth at larger relative embedment ratios. Although further research is necessary, these results lay the basis for the development of a new generation of design criteria for determining anchor capacity at the ultimate limiting state.

An Experimental Investigation of Piping Effects on the Mechanical Properties of Toyoura Sand

Piping is a complicated natural phenomenon of internal erosion, which threatens the safety of hydraulic earth structures. Despite of the comprehensive research aiming to figure out the onset condition and development of piping, there is little element experiment in laboratory regarding the mechanical properties of disturbed soil. In this paper, as an attempt to create piping erosion under controlled conditions, glucose with certain shape and volume was placed in sand samples. With the dissolution of glucose pipes, artificial piping erosion was reproduced. Based on this approach, a series of experiments were performed in a hollow cylindrical torsional shear apparatus under different confining pressures for both intact specimens and eroded ones. Strains during piping propagation were measured by local sensors. Shear modulus was obtained by conducting torsional cyclic loadings with peak to peak stress magnitude of 4 kPa under various directions of principal stress axes. Furthermore, shear strength and the development of shear band were studied. The results clearly indicate the weakened mechanical behavior of sand subjected to piping erosion. Influence of piping-induced anisotropic fabric on shear strength and shear band was also confirmed.

Peak stresses shift from femoral tunnel aperture to tibial tunnel aperture in lateral tibial tunnel ACL reconstructions: a 3D graft-bending angle measurement and finite-element analysis.

To investigate the effect of tibial tunnel orientation on graft-bending angle and stress distribution in the ACL graft. Eight cadaveric knees were scanned in extension, 45°, 90°, and full flexion. 3D reconstructions with anatomically placed anterior cruciate ligament (ACL) grafts were constructed with Mimics 14.12®. 3D graft-bending angles were measured for classic medial tibial tunnels (MTT) and lateral tibial tunnels (LTT) with different drill-guide angles (DGA) (45°, 55°, 65°, and 75°). A pivot shift was performed on 1 knee in a finite-element analysis. The peak stresses in the graft were calculated for eight different tibial tunnel orientations. In a classic anatomical ACL repair, the largest graft-bending angle and peak stresses are seen at the femoral tunnel aperture. The use of a different DGA at the tibial side does not change the graft-bending angle at the femoral side or magnitude of peak stresses significantly. When using LTT, the largest graft-bending angles and peak stresses are seen at the tibial tunnel aperture. In a classic anatomical ACL repair, peak stresses in the ACL graft are found at the femoral tunnel aperture. When an LTT is used, peak stresses are similar compared to classic ACL repairs, but the location of the peak stress will shift from the femoral tunnel aperture towards the tibial tunnel aperture. the risk of graft rupture is similar for both MTTs and LTTs, but the location of graft rupture changes from the femoral tunnel aperture towards the tibial tunnel aperture, respectively. I.

Assessment of residual stress of 7050-T7452 aluminum alloy forging using the contour method

The cold-compression stress relief process has been used to reduce the quench-induced stresses in high-strength aerospace aluminum alloy forgings. However, this method does not completely relieve the stress. Longitudinal residual stresses in 7050-T7452 aluminum alloy forging were measured with contour method. The measuring procedure of the contour method including specimen cutting under clamps with a wire electrical discharge machine, contour measurement of the cut surface with a laser scanner, careful data processing and elastic finite element analysis was introduced in detail. In addition, multiple cuts were used to map cross sectional stress at different cut surfaces. Finally, the longitudinal residual stress throughout the cut plane was mapped, and through thickness longitudinal stress profiles were also analyzed. Investigated results suggest that spatial variation of stress distribution can be attributed to the non-uniform plastic deformation of the cold-compression stress relief process. The overall reduction of peak stress magnitudes is approximately 43–79%.

Effect of Acetabular Orientation on Stress Distribution of Highly Cross-linked Polyethylene Liners

Several case reports have documented the fracture of highly cross-linked polyethylene (HCLPE) liners used in total hip arthroplasty (THA). Although uncommon, fractured liners result in considerable morbidity for patients and require revision surgery. One postulated mechanism that leads to this type of implant failure is malorientation of the acetabular component. The purpose of this study was to investigate the effect of acetabular orientation on the stress distribution of HCLPE liners used in THA by means of finite element analysis. Three-dimensional models of a commonly used HCLPE liner were created corresponding to 12 different acetabular component orientations (inclination ranging from 20° to 70° and version ranging from 20° of retroversion to 40° of anteversion). A static stress analysis of the finite element models was performed under conditions simulating peak gait loads. The results of the analysis revealed that excessive inclination and extremes of version were associated with an increase in peak stress magnitudes. The locations of peak stress also were found to lie within the rim notch and locking ring groove regions, which were consistent with the fracture locations reported in published case reports. Therefore, the acetabular component should be oriented carefully during implantation to reduce the risk of rim loading and subsequent liner fracture. In addition, an alternative liner design may further help reduce stress risers and risk of fracture.

3D FE delamination induced damage analyses of adhesive bonded lap shear joints made with curved laminated FRP composite panels

This paper deals with the evaluation of inter-laminar stresses in the adhesive layer existing between the lap and the strap adherends of lap shear joints (LSJ) made with curved laminated fibre reinforced plastic (FRP) composite panels for varied embedded delaminations between the first and second plies of the strap adherend. Non-linear finite element analyses have been carried out using contact and multi point constraint (MPC) elements. The use of contact elements ensures avoidance of inter-penetration of delaminated surfaces. Sequential release of MPC elements facilitates computation of individual modes of Strain Energy Release Rates (SERR). The effects of varied delamination lengths on variations of peel and inter-laminar shear stresses and different modes of SERR are seen to be very significant. Their variations on both the delamination fronts, for each size of the delamination, are found to be much different from each other indicating different propagation rates at the two delamination fronts. The structural integrity of the LSJ in the presence of delaminations, thus, can be predicted with adaptive finite element (FE) simulations. It is further seen that the peak stress magnitudes and SERRs are higher in the LSJs made with curved FRP composite panels as compared to the flat laminates. This may be due to the stiffening effects induced by the curvature geometry of the curved composite panels.

The influence of axial image resolution on atherosclerotic plaque stress computations

Biomechanical models are used extensively to study risk factors, such as peak stresses, for vulnerable atherosclerotic plaque rupture. Typically, 3D patient-specific arterial models are reconstructed by interpolating between cross sectional contour data which have a certain axial sampling, or image, resolution. The influence of the axial sampling resolution on computed stresses, as well as the comparison of 3D with 2D simulations, is quantified in this study. A set of histological data of four atherosclerotic human coronary arteries was used which were reconstructed in 3D with a high sampling (HS) and low sampling (LS) axial resolution, and 4 slices were treated separately for 2D simulations. Stresses were calculated using finite element analysis (FEA). High stresses were found in thin cap regions and regions of thin vessel walls, low stresses were found inside the necrotic cores and media and adventitia layers. Axial sampling resolution was found to have a minor effect on general stress distributions, peak plaque/cap stress locations and the relationship between peak cap stress and minimum cap thickness. Axial sampling resolution did have a profound influence on the error in computed magnitude of peak plaque/cap stresses (±15.5% for HS vs. LS geometries and ±24.0% for HS vs. 2D geometries for cap stresses). The findings of this study show that axial under sampling does not influence the qualitative stress distribution significantly but that high axially sampled 3D models are needed when accurate computation of peak stress magnitudes is required.

Osteochondral Lesions of the Talus

Background: Osteochondral lesions of the talus (OLTs) are a common cause of ankle pain and disability. Current clinical guidelines favor autogenous or allogenic osteochondral grafting procedures for lesions larger than 10 mm in diameter because of increased failure rates in these larger lesions with arthroscopic debridement, curettage, and microfracture. There are currently no biomechanical data nor level I clinical data supporting this size threshold. Purpose: The purpose of this study was to determine the effect of OLT defect size on stress concentration, rim stress, and location of peak stress and whether a threshold defect size exists. Study Design: Descriptive laboratory study. Methods: Progressively larger medial OLTs were created (6, 8, 10, and 12 mm) in 8 fresh-frozen cadaveric ankle joints. With a calibrated Tekscan pressure sensor in the tibiotalar joint, an axial load of 686 N was applied, and pressure was recorded in neutral and 15° of plantar flexion with each defect size. Peak stress, contact area, peak and average rim stresses, and location of peak stress were determined. Results: The distance between peak stress and defect rim was significantly decreased with increasing defect size for lesions of 10 mm and larger. Total tibiotalar contact area was significantly decreased with increasing defect size and with ankle plantar flexion. While peak joint stress and peak rim stress were not affected by defect size or plantar flexion, average rim stress was significantly increased by plantar flexion. Conclusion: Reduction in contact area and shift in the location of peak stress with increasing defect size may contribute to articular cartilage degeneration, pain, and defect enlargement in patients with OLTs. There appears to be a threshold of 10 mm after which the distance between the rim of the defect and the peak stress decreases; however, there is no change in peak stress magnitude with increasing defect size. Clinical Relevance: The location of peak stress in the ankle joint becomes closer to the rim of the defect in OLTs at a threshold of 10 mm and greater in diameter. These data may have implications toward OLT size thresholds for surgical decision making in symptomatic lesions (ie, primary osteochondral transplantation procedure vs curettage and debridement). The ultimate goal is to determine whether there is a threshold defect size for primary osteoarticular graft techniques.

Mechanical stress, fracture risk and beak evolution in Darwin's ground finches ( Geospiza )

Darwin's finches have radiated from a common ancestor into 14 descendent species, each specializing on distinct food resources and evolving divergent beak forms. Beak morphology in the ground finches (Geospiza) has been shown to evolve via natural selection in response to variation in food type, food availability and interspecific competition for food. From a mechanical perspective, however, beak size and shape are only indirectly related to birds' abilities to crack seeds, and beak form is hypothesized to evolve mainly under selection for fracture avoidance. Here, we test the fracture-avoidance hypothesis using finite-element modelling. We find that across species, mechanical loading is similar and approaches reported values of bone strength, thus suggesting pervasive selection on fracture avoidance. Additionally, deep and wide beaks are better suited for dissipating stress than are more elongate beaks when scaled to common sizes and loadings. Our results illustrate that deep and wide beaks in ground finches enable reduction of areas with high stress and peak stress magnitudes, allowing birds to crack hard seeds while limiting the risk of beak failure. These results may explain strong selection on beak depth and width in natural populations of Darwin's finches.

Computational Studies of Strain Exposures in Neonate and Mature Rat Brains during Closed Head Impact

Traumatic brain injury (TBI) is the most common cause of death in childhood, and the majority of fatal cases are due to motor vehicle accidents, falls, sport-related accidents, and child abuse. Rodents and particularly rats became a commonly used animal model of TBI in childhood as well as in adults, and different techniques are described in the literature to induce the brain injury. However, findings reported in the last decade regarding the increased stiffness of brain tissue in young animals, including rats, are not considered in experimental designs of TBI studies, and this may seriously bias the results when TBI effects are compared across different animal ages. In this study, we determined the strain and stress distributions in neonatal (post-natal-day [PND] 13-17) and mature (PND 43 and 90) rat brains during a closed head injury, using age-specific finite element (FE) models. The FE simulations indicated that for identical cortical displacements, the neonatal brain may be exposed to larger peak stress magnitudes compared with a mature brain due to stiffer tissue properties in the neonate, as well as larger strain magnitudes due to its smaller size. The brain volume subjected to a certain strain level was greater in the neonate brain compared with the adult models for all indentation depths greater than 1 mm. In conclusion, our present findings allow better design of closed head impact experiments which involve an age factor. Additionally, the larger peak stresses and larger strain volumetric exposures observed in the neonatal brain support the hypothesis that the smaller size and stiffer tissue of the infant brain makes it more susceptible to TBI.

Analysis of Stress Concentrations in 2 2 Braided Composites

The stress distribution in braided composites is complex even for simple uniaxial loading. The interlacing of the tows creates a complex load path that results in full three-dimensional (3D) stress distribution. The location and magnitude of peak stresses depend on the particular stress component and vary with various braid architecture parameters such as braid angle and degree of waviness. Finite element analyzes for different braids were performed and it was seen that the peak stresses in the tow mainly occur at the undulating region and along the edges of the tow. Stress distribution in braids was compared with those in ‘equivalent laminates’. A considerable volume of the tow (10-45% for the considered range of parameters) had stresses larger than an ‘equivalent lamina’. The severity of stresses in a braid as compared to those in an equivalent lamina depends upon braid geometric parameters. Braid angle changes the stress distribution in the tow considerably. However, most of that effect is due to the orientation of the tows in the + and directions and can be eliminated by matching the loading on the tow of different braids. The severity of peak stresses seems to be increasing linearly with an increase in waviness ratio.

Damping effects on the response of maxillary incisor subjected to a traumatic impact force: A nonlinear finite element analysis

The aim of this study was to evaluate the effects of damping on stress concentration in an impacted incisor. Damping ratios of maxillary incisors were tested using an in vivo modal testing method. A finite element model of the upper central incisor was established for dental trauma analysis. To assess the effect of damping properties on induced stresses in the traumatized incisors, equivalent stresses in the finite element model with various damping ratios were calculated for comparison. The mechanisms of cushioning properties of the upper incisors on traumatic injuries were assessed by profiling the stress distributions in the incisor model sequentially with time. The measured damping ratio of maxillary incisors was 0.146+/-0.037. When the incisor was subjected to an impact force, high stresses were concentrated at the labial and lingual incisor edges, cervical ridge, and the area around root apex. When the damping ratios of the incisor model were set at 10- and 50-fold of the measured values, the peak stresses induced near the impact site of the incisor model were reduced from 24.0 to 23.2 and 15.9 MPa, respectively. On the other hand, the peak stress lagged and the stress existence period increased when the damping properties were taken into consideration. Damping properties of teeth provide protection to the tooth during traumatic injury by decreasing the peak stress magnitude due to release of strain energy over a longer period.