Significance of the Relative Orientation of the Mean and Alternating Principal Stress Axes in Biaxial Fatigue

1992 ◽  
Vol 114 (4) ◽  
pp. 406-408 ◽  
Author(s):  
E. G. Munday
Keyword(s):  
Principal Stress ◽  
Fatigue Behavior ◽  
Fatigue Analysis ◽  
Relative Orientation ◽  
Biaxial Fatigue ◽  
Stress Components ◽  
The Mean ◽  
Long Life ◽  
Existing Data

In certain biaxial fatigue problems, the stress components can be represented as a superposition of mean components, and proportionally applied alternating components. Such representation is the first step in applying some of the more popular methods for long-life fatigue analysis. It is commonly assumed, perhaps unwittingly, that the relative orientation of the mean and alternating principal stress axes does not influence fatigue behavior. It is explained how this assumption is inherent in several popular methods. It is pointed out that the validity of the assumption cannot be demonstrated by existing data.

The Effect of Mean Stress Components in High-Cycle, Biaxial Fatigue

2003 ◽  
Vol 31 (2) ◽  
pp. 177-186 ◽  
Author(s):  
Edgar G. Munday
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Relative Orientation ◽  
New Method ◽  
Mean Stress ◽  
Time Varying ◽  
Biaxial Fatigue ◽  
Stress Components ◽  
The Mean

A new method is presented to obtain the effect of mean stress components in high-cycle, biaxial fatigue. It is assumed that the time-varying stress state can be represented as a superposition of mean components, and proportionally applied alternating components. The method takes into account the relative orientation of the mean and alternating principal stress axes by making the ‘equivalent mean stress’ depend on the alternating components as well as the mean stress components. The method correlates well with the available data. The new method is compared with three popular methods.

The Effect of Mean Stress on the Fatigue Behavior of Woven-Roving Glass Fiber-Reinforced Polyester Subjected to Torsional Moments

2005 ◽  
Vol 127 (3) ◽  
pp. 301-309 ◽  
Author(s):  
Mohamed N. A. Nasr ◽  
M. N. Abouelwafa ◽  
A. Gomaa ◽  
A. Hamdy ◽  
E. Morsi
Keyword(s):  
Glass Fiber ◽  
Detrimental Effect ◽  
Fatigue Behavior ◽  
Local Stress ◽  
Mean Stress ◽  
Glass Fiber Reinforced ◽  
Stress Components ◽  
Amplitude Component ◽  
The Mean ◽  
Stress Ratios

The effect of torsional mean stress on the fatigue behavior of glass fiber-reinforced polyester (GFRP) is studied by testing thin-walled, woven-roving tubular specimens with two fiber orientations, [±45°]2s and [0,90°]2s, at negative stress ratios (R),R=−1,−0.75,−0.5,−0.25, 0. The [±45°]2s specimens were found to have higher fatigue strength than the [0,90°]2s specimens at all stress ratios. This is attributed to the difference in local stress components, the [±45°]2s specimens being subjected to tension-compression local stress components, while the [0,90°]2s specimens being subjected to pure local shear stress. For the studied stress ratios; the mean stress component had a detrimental effect on the amplitude component for the [±45°]2s specimens; while it was ineffective for the [0,90°]2s specimens in a certain region in the mean-amplitude diagram, region (1), then it had a detrimental effect in the rest of the diagram, region (2). The S–N curves for positive stress ratios were extrapolated from those for negative stress ratios, which were found experimentally, for the [0,90°]2s specimens. The positive stress ratio points, having the same local stress state as the negative ones, showed an acceptable behavior tending to decrease the amplitude component for the same life.

scholarly journals Perception of facial appearance and profile among Bangladeshi Laypersons

2018 ◽  
Vol 17 (4) ◽  
pp. 638-643
Author(s):  
Mohammad Khursheed Alam ◽  
Shifat A Nowrin
Keyword(s):  
Soft Tissue ◽  
Orthodontic Treatment ◽  
Medical Science ◽  
Satisfaction Score ◽  
Facial Appearance ◽  
Soft Tissue Profile ◽  
Average Profile ◽  
The Mean ◽  
Existing Data ◽  
Structured Questionnaire

Background: Enlightening facial esthetic is reflecting as one of the main influences in orthodontic treatment during establishing of ideal occlusion.Method: In present study, a determination was made to subsidize to the existing pool of information on the soft-tissue profile and facial awareness. Main aim of the study is to investigate how the Bangladeshi laypersons are aware of their own faces by analyzing the data collected through a structured questionnaire.Result: This study involved total 200 Bangladeshi Individuals age ranged 19 to 23 years old. A validated structured questionnaire was used to assess subjects’ evaluation of their own facial appearance. The mean awareness score for the subjects of Bangladeshi individuals ranged from 1.4 to 2.3 in male and from 1.7 to 1.9 in female for the overall impressions and from 1.3 to 2.1 in male and from 1.2 to 2.3 in female for the facial parts. Satisfaction score for the 9 items out of 24 items differed significantly between Bangladeshi female and male. An average profile of the jaw and lips are desired over more retrusive or protrusive profiles among Bangladeshi laypersons.Conclusion: It can be determined that Bangladeshi laypersons are adept to understand their own faces in the various commands and most of the peoples are worry about their profile in their everyday survives. We must evaluate our existing data to find orthodontic standards that are valid for specific ethnic groups.Bangladesh Journal of Medical Science Vol.17(4) 2018 p.638-643

Comparison of Three Different Screw Trajectories in Osteoporotic Vertebrae: A Biomechanical Investigation

2020 ◽  
Author(s):  
Jan-Sven Jarvers ◽  
Stefan Schleifenbaum ◽  
Christian Pfeifle ◽  
Christoph Oefner ◽  
Melanie Edel ◽  
...  
Keyword(s):  
Cortical Bone ◽  
Fatigue Behavior ◽  
Fixation Strength ◽  
Patient Specific ◽  
Promising Alternative ◽  
Cortical Bone Trajectory ◽  
Pull Out ◽  
Group A ◽  
The Mean ◽  
Group B

Abstract Background: Pedicle screw insertion in osteoporotic patients is challenging. Achieving more screw-cortical bone purchase and invasiveness minimization, the cortical bone trajectory and the midline cortical techniques represent alternatives to traditional pedicle screws. This study compares the fatigue behavior and fixation strength of the cement-augmented traditional trajectory (TT), the cortical bone trajectory (CBT) and the midline cortical (MC). Methods: Ten human cadaveric spine specimens (L1 - L5) were examined. The average age was 86.3 ± 7.2 years. CT scans were provided for preoperative planning. CBT and MC were implanted by using the patient-specific 3D-printed placement guide (MySpine®, Medacta International), TT were implanted freehand. All 10 cadaveric specimens were randomized to group A (CBT vs. MC) or group B (MC vs. TT). Each screw was loaded for 10,000 cycles. The failure criterion was doubling of the initial screw displacement resulting from the compressive force (60 N) at the first cycle, the stop criterion as a doubling of the initial screw displacement. After dynamic testing, screws were pulled out axially at 5 mm/min to determine their remaining fixation strength. Results: The mean pull-out forces did not differ significantly. Concerning the fatigue performance, only one out of ten MC of group A failed prematurely due to loosening after 1,500 cycles (L3). Five CBT already loosened during the first 500 cycles. The mean displacement was always lower in the MC. In group B, all TT showed no signs of failure or loosening. Three MC failed already after 26 cycles, 1,510 cycles, and 2,144 cycles, respectively. The TT showed always a lower mean displacement. In the subsequent pull-out tests, the remaining mean fixation strength of the MC (449.6 ± 298.9 N) was slightly higher compared to the mean pull-out force of the CBT (401.2 ± 261.4 N). However, MC (714.5 ± 488.0 N) were inferior to TT (990.2 ± 451.9 N).Conclusion: The current study demonstrated that cement-augmented TT have best fatigue and pull-out characteristics in osteoporotic lumbar vertebrae, followed by the MC and CBT. MC represent a promising alternative in osteoporotic bone if cement augmentation should be avoided. Using the patient-specific guide contributes to improve screws’ biomechanical properties.

scholarly journals Taxonomic significance of some leaf anatomical features of the species of Annona L. (annonaceae) from Nigeria

2020 ◽  
Vol 22 (1) ◽  
pp. 101-112
Author(s):  
S.A. Adeniran ◽  
A.B. Kadiri ◽  
J.D. Olowokudejo
Keyword(s):  
Vascular Bundles ◽  
Taxonomic Significance ◽  
Anticlinal Wall ◽  
Abaxial Surface ◽  
Anatomical Features ◽  
Qualitative And Quantitative ◽  
Dichotomous Key ◽  
The Mean ◽  
Generic Constant ◽  
Existing Data

A comparative study of the some leaf anatomical features of four species of Annona occurring in Nigerian was undertaken with the aid of light microscope. The four foliar structures (epidermis, petiole, midrib and lamina architecture) studied revealed useful characters which support recognition of the species. A combination of these features has been used to prepare an artificial indented dichotomous key for identifying the  species. The generic constant features encountered included hypostomata, paracytic stomatal type, linear nerves endings, uneven midrib outline, and centrally located vascular bundles in the petiole and midrib. However, the most reliable distinguishing characters found across the species included presence of brachyparacytic stomata in A. reticulata, presence of trichomes on the midrib in A. senegalensis, absence of druses on the abaxial surface in A. muricata and A. squamosa, a thick pitted anticlinal walls on the surfaces of A. muricata and consistent polygonal areola shape in A. squamosa. The overlapping characters which also justify the closeness of the species and their grouping in a genus were recorded in both the qualitative and quantitative features. Prominent among them are the mean stomatal width which is about 1.0 μm in all species, nerve endings within the areole which varies between 1-2, U- or V-shaped midrib on the adaxial surface and straight to curved anticlinal wall pattern. The significance of these observations is discussed in updating the existing data in the genus. Keywords: Epidermis, Microscopy, Midrib, Petiole,   Systematic

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