Cover Image, Volume 48, Issue 2 Ai, Zhi Yong; Ye, Zi Kun; Huang, Hong Wei ...
International journal for numerical and analytical methods in geomechanics,
02/2024, Volume:
48, Issue:
2
Journal Article
Peer reviewed
Open access
The cover image is based on the Research Article Stress analysis of elliptical tunnels in an orthogonally anisotropic elastic full‐space under non‐uniform in‐situ stress by Zhi Yong Ai et al., ...https://doi.org/10.1002/nag.3649.
Two data evaluation concepts for X‐ray stress analysis based on energy‐dispersive diffraction on polycrystalline materials with cubic crystal structure, almost random crystallographic texture and ...strong single‐crystal elastic anisotropy are subjected to comparative assessment. The aim is the study of the residual stress state in hard‐to‐reach measurement points, for which the sin2ψ method is not applicable due to beam shadowing at larger sample tilting. This makes the approaches attractive for stress analysis in engineering parts with complex shapes, for example. Both approaches are based on the assumption of a biaxial stress state within the irradiated sample volume. They exploit in different ways the elastic anisotropy of individual crystallites acting at the microscopic scale and the anisotropy imposed on the material by the near‐surface stress state at the macroscopic scale. They therefore complement each other, in terms of both their preconditions and their results. The first approach is based on the evaluation of strain differences, which makes it less sensitive to variations in the strain‐free lattice parameter a0. Since it assumes a homogeneous stress state within the irradiated sample volume, it provides an average value of the in‐plane stresses. The second approach exploits the sensitivity of the lattice strain to changes in a0. Consequently, it assumes a homogeneous chemical composition but provides a stress profile within the information depth. Experimental examples from different fields in materials science, namely shot peening of austenitic steel and in situ stress analysis during welding, are presented to demonstrate the suitability of the proposed methods.
The single‐crystal elastic anisotropy and the anisotropy of the near‐surface (residual) stress state of polycrystalline materials with random texture are exploited in energy‐dispersive X‐ray stress analysis to study samples under constrained measurement conditions.
•An analytical model is established for bonded joints with functionally graded adherends.•Critical locations of stress concentration are identified.•Methods to reduce stress concentrations are ...proposed.
Adhesively bonded joints with functionally graded (FG) adherends are of practical significance since tailoring material composition through the adherend thickness can lead to more uniform shear or peeling stress distributions in the adherends and the adhesive layer near the edges of the joint. Stresses at the free edges of the adhesive layer have been found to be critical to the integrity of the joint. To this end, an analytical model is proposed for an adhesively bonded single lap joint with FG adherends. In this model, the adhesive layer is modeled as a three parameter, elastic foundation, allowing for different peel stress values at the two adherend-adhesive interfaces. Closed-form expressions for interface stresses and internal forces in the adherends are obtained. The model is validated by its agreement with finite element analysis simulations. This model shows that the peel stresses are critical at the left edge of the upper adherend-adhesive interface and at the right edge of the lower adherend–adhesive interface, suggesting that the joint is vulnerable to delaminations along the upper adherend-adhesive interface at the left edge and along the lower adherend-adhesive interface at the right edge. Parametric studies reveal the effects of adhesive thickness, adhesive stiffness, and FGM configuration on the stresses within the single lap joint. Results show that stress concentrations can be reduced near the edges of the joint by increasing the thickness of the adhesive layer, reducing the Young’s modulus of the adhesive layer, and/or configuring the FG adherends so that the stiffer material is nearest the adhesive layer.
Objectives
To analyze the stress distribution and subsequent fracture resistance of human maxillary premolars with mesial-occlusal-distal (MOD) defects restored with different minimally invasive ...restorations.
Materials and methods
Seventy non-carious human maxillary premolars were selected and divided into seven groups (n = 10). Ten teeth without further preparation served as control. The remaining teeth were endodontically treated and received three restorative patterns: inlays without cusp coverage (I), onlays with palatal coverage (O), overlays with both buccal and palatal coverage (Ov). Lithium disilicate glass ceramics (EM) and machinable composite resin (LU) were used for restoration. Specimens were tested under cycling loading with tongue direction of 45° for 1.2 × 10
6
cycles at a 50-N load and 2.0-Hz frequency. The survival time and two fracture mode classifications were assessed. Three-dimensional models of each group were designed. The magnitude and pattern of stresses were analyzed under the same condition of the in vitro test using finite element stress analysis.
Results
Although the overlay model pattern produced more favorable stress distribution, three restorative patterns restored with the same material had no difference in survival curves (
P
> 0.05). Only the survival curve of the EM-Ov group had no statistical difference with that of the control group (
P
> 0.05). EM groups presented mainly interface adhesive failure, while LU groups were mainly material cohesive failure.
Conclusion
For the endodontically treated maxillary premolars with MOD defect, the lithium disilicate glass ceramic overlay pattern can reach the best restorative effect.
Clinical relevance
Comparing with restorative pattern, restorative material had a greater influence on the minimally invasive restoration of posterior teeth.
The residual stresses at a circular punched end face in tempered martensitic high-strength steel sheets were investigated using triaxial stress analysis via X-ray diffraction. The maximum principal ...stress and its direction were calculated from the measured nine stress components. The relationship between the directions of the maximum principal stress and hydrogen cracks was verified by generating hydrogen cracks on the punched end face in the same specimen using cathodic hydrogen charging. The direction of the cracks was perpendicular to that of the maximum principal stress. This result indicates that hydrogen embrittlement at the sheared end face is caused by the maximum principal stress. Moreover, the distribution of the residual stresses toward the thickness direction and the relationship between residual stresses and tensile strength of the specimens were investigated. The maximum principal stress on the punch side was lower than that on the dice side. Unlike the maximum principal stresses, the normal stresses did not increase monotonically with the tensile strength of the specimens. Therefore, it was concluded that investigating the maximum principal stress at any area between the dice side and a line located midway from the end face and dice side is crucial for considering the hydrogen embrittlement criteria.
Polymerization shrinkage stress of resin-based materials have been related to several unwanted clinical consequences, such as enamel crack propagation, cusp deflection, marginal and internal gaps, ...and decreased bond strength. Despite the absence of strong evidence relating polymerization shrinkage to secondary caries or fracture of posterior teeth, shrinkage stress has been associated with post-operative sensitivity and marginal stain. The latter is often erroneously used as a criterion for replacement of composite restorations. Therefore, an indirect correlation can emerge between shrinkage stress and the longevity of composite restorations or resin-bonded ceramic restorations. The relationship between shrinkage and stress can be best studied in laboratory experiments and a combination of various methodologies. The objective of this review article is to discuss the concept and consequences of polymerization shrinkage and shrinkage stress of composite resins and resin cements. Literature relating to polymerization shrinkage and shrinkage stress generation, research methodologies, and contributing factors are selected and reviewed. Clinical techniques that could reduce shrinkage stress and new developments on low-shrink dental materials are also discussed.
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