ABSTRACT
In order to evaluate the safety performance of self-expandable NiTi alloy stents systematically, the dynamic safety factor drawn up by International Organization for Standardization, was used to quantitatively reflect the safety performance of stents. Based on the constitutive model of super-elastic memory alloy material in Abaqus and uniaxial tensile test data of NiTi alloy tube, finite element method and experiments on accelerated fatigue life were carried out to simulate the self-expansion process and the shape change process under the action of high and low blood pressure for three -type stents of 8×30 mm, 10×30 mm, 12×30 mm. By analyzing the changes of stress and strain of self-expanding NiTi alloy stent, the maximum stress and strain, stress concentration position, fatigue strength and possible failure modes were studied, thus the dynamic safety factor of stent was calculated. The results showed that the maximum stress and plastic strain of the stent increased with the increase of grip pressure, but the maximum stress and strain distribution area of the stent had no significant change, which were all concentrated in the inner arc between the support and the connector. The dynamic safety factors of the three stents were 1.31, 1.23 and 1.14, respectively, which indicates that the three stents have better safety and reliability, and can meet the fatigue life requirements of more than 10 years, and safety performance of the three stents decreases with the increase of stent's original diameter.
Subject(s)
Alloys , Finite Element Analysis , Nickel , Reproducibility of Results , Self Expandable Metallic Stents , Stress, Mechanical , TitaniumABSTRACT
The mechanical properties of nitinol iliac vein stent (NIVS) have been studied by many scholars at home and abroad, but the study on the mechanical properties of iliac vein stent under different release scales has not been reported yet. Based on the finite element analysis method, the mechanical properties of three self-developed NIVS were studied to reveal the influence of stent diameters (12, 14, 16 mm) and different release scales (80%, 90%) on its strength, fatigue life and vein wall biomechanical properties. With an increases in the release scales, the equivalent elastic strain, fatigue strength safety factors, and vessel wall equivalent stress exhibited a downward trend, while the most stressed cross-section coincided with the arc of stent-connecting rods. Through 30, 60 and 90 days' animal test, a narrowed vascular model was established in the iliac veins of 12 pigs, and the developed iliac vein stents were implanted to comprehensively evaluate the safety and effectiveness of the stent, and at the same time the mechanical properties of stents were verified to provide important reference for the type inspection and clinical trials of follow-up products.
Subject(s)
Animals , Alloys , Finite Element Analysis , Iliac Vein , Stents , Stress, Mechanical , SwineABSTRACT
Objective To analyze the relationship between fatigue strength and connector length of intracranial artery stents, so as to investigate the exact location of fatigue fracture for the stent. Methods The fatigue life for 3 kinds of artery stents were analyzed by finite element analysis method of fatigue fracture, and distribution map of dangerous points was drawn by means of Goodman curve. Based on F2477-07 standard from American Society for Testing and Materials (ASTM), the fatigue life for 3 kinds of stents was tested. Results If the length of the support connector was longer, the maximum equivalent stress and the average stress in dangerous points of the stent would be larger. If the distribution of dangerous points was more close to the curve of fatigue limit, and fatigue fracture was more likely to occur in the stent. Goodman curves indicated that 3 kinds of stents was safe to be used in the body for ten years. Finite element analysis and experimental result showed that fatigue life near the stent junction was relatively lower, and dangerous points of the stent was located at the arc junction. Conclusions It is reasonable to study stents by finite element analysis, whose results are basically coincided with the experimental data. Fatigue life can be extended by reducing connector’s length for the design of stent structure.
ABSTRACT
Objective To measure the quality of manual wheelchairs made in China. Methods 20 wheelchairs was tested with ISO 7176-8, focused on the static strength, impact strength and fatigue strength. Results 8 (40%) wheelchairs passed the test. Conclusion The fa-tigue strength is the key factor of the wheelchair quality.
ABSTRACT
@#Objective To measure the quality of manual wheelchairs made in China. Methods 20 wheelchairs was tested with ISO 7176-8, focused on the static strength, impact strength and fatigue strength. Results 8 (40%) wheelchairs passed the test. Conclusion The fatigue strength is the key factor of the wheelchair quality.
ABSTRACT
Hip joint, bearing and transmitting the major part of our body weight, is very vulnerable to damage, which may be further accentuated by certain factors like osteoarthritis, rheumatoid arthritis, avascular necrosis of femoral head following fracture neck femur, tumour, osteoporosis or any type of street accident. Of them single most determining factor is osteoporosis – observed in most of the postmenopausal women which may be further magnified by lack of proper nutrition in a developing country like India. When these factors become chronic and debilitating, leading to severe pain, restriction of mobility and function; – need for the complete or partial hip arthroplasty comes to play. Number of patients suffer every year throughout the world is well over 10 lakh and the figure in India is about 4 lakh. In India however, number of hip operation every year is much lower (about 1 lakh)1 as most of our patients cannot afford the prosthesis and operation cost. Again, while opting for surgery, along with cost other factors like the material itself or its efficacy should be considered. The most popular material, which is in vogue internationally, is ceramic on ceramic prosthesis which is now considered to be the best material.
Subject(s)
Femoral Fractures/therapy , Ceramics/chemistry , Hip Prosthesis/economics , Humans , Materials Testing , Mechanical Phenomena , Stress, Mechanical , Walking , Weight-BearingABSTRACT
Background : Though acrylic resins possess many desirable properties, denture fracture due to flexural fatigue or impact failure is a common problem. One major factor influencing the flexural fatigue strength of denture base resins is the processing technique used. Aim: To measure the flexural fatigue strength of denture base resins polymerized using short and long curing cycles using water bath, pressure cooker, and microwave polymerization techniques. Materials and Methods: Flexural fatigue strength of 60 samples (n=10) were measured using a cyclic 3-point loading method on a dynamic universal testing machine. Data were analyzed using a Student 't' test. Results : Comparative evaluation using Student's 't' test of mean flexural fatigue strength of samples processed by water bath processing (660.6) and the microwave technique (893.6) showed statistically significant (P <0.01) result with microwave processing being higher. Comparison of water bath (660.6) and pressure cooker (740.6) processing and microwave (893.6) and pressure cooker (740.6) processing using Student's 't' test was not statistically significant (P >0.05). In the intra-group analysis, it was found that there was statistically significant difference in samples processed using the short and long curing cycle, the latter being better in all groups, P-values being <0.05, <0.001, and <0.001 for water bath, microwave, and pressure cooker polymerization techniques, respectively. Conclusion : The polymerization procedure plays an important role in influencing the flexural fatigue strength of denture base resins, and the microwave long curing processing technique produced denture bases with highest flexural fatigue strength.
Subject(s)
Acrylic Resins/chemistry , Acrylic Resins/radiation effects , Dental Materials/chemistry , Dental Materials/radiation effects , Dental Stress Analysis/instrumentation , Denture Bases , Elastic Modulus , Humans , Materials Testing , Methylmethacrylate/chemistry , Methylmethacrylate/radiation effects , Microwaves , Pliability , Polymerization , Polymethyl Methacrylate/chemistry , Polymethyl Methacrylate/radiation effects , Pressure , Stress, Mechanical , Time Factors , Water/chemistryABSTRACT
Objective:To investigate the corrosion fatigue strength of laser-welded specimens fabricated from commercially pure titanium (TA2) and titanium alloy(TC4). Methods:TA2 and TC4 were mechanically processed into a certain size and joined by laser welding. A fatigue testing machine was used to test tensile load and fatigue strength after soaked in synthetic saliva. The fatigue fracture surface was examined by scanning electron microscopy (SEM). Results: The fatigue strengths of the laser-welded test specimens showed no significant differences compared to specimens in air. SEM examination showed that there were no defects such as corrosion pits. Conclusion: There are no significant differences between either laser-welded metal in the corrosion fatigue strength for dry specimens and specimens in synthetic saliva.
ABSTRACT
Current dental restorations present a relatively weak resistance to fracture. Owing to their unique mechanical properties, fibre-reinforced polymers are now being considered. Unidirectional or woven continuous fibres, made of glass, polyethylene, carbon or Kevlar, have been evaluated. This study focused on the use of glass fibre knitted fabrics to reinforce acrylate resins, in order to investigate the possibility to construct single crowns as well as three unit bridges. Some points affecting the final composite system were tested: 1) static strength, with focus on the stress transfer under a occlusal contact point; 2) modelling of a three unit bridge; 3) fatigue strength as a posterior three unit bridge material. The study demonstrated that knitted fabric reinforcements are showing an interesting compromise between stiffness, static strength for single crown. For three unit bridge applications in the posterior arch, however, knitted glass fabric reinforcements were not strong enough in fatigue. An additional reinforcement in the posterior arch fixed partial denture design was recommended.