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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Fatigue & fracture of engineering materials & structures 25 (2002), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Fatigue & fracture of engineering materials & structures 23 (2000), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Acrylic bone cement is used as a fixing device in total hip arthroplasty and it is based on polymethyl-methacrylate. Fatigue failure of the cement is the primary cause of loosening of cemented arthroplasties. Pores form in the acrylic material during mixing and curing, and an analysis of the fatigue life of the cement requires the elimination of the critical macropores, defined as having a diameter 〉 1 mm, which may bias the outcome of tests. Previous workers have rejected fatigue specimens either on a qualitative basis or at a specified pore size level. However various different thresholds have been considered but currently there is no quantitative criterion to define them. This investigation proposes a quantitative criterion for establishing a critical macropore size rejection threshold for fatigue specimens, and discusses the effectiveness of this criterion based on fatigue tests of radiopaque cement specimens.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Archives of orthopaedic and trauma surgery 116 (1997), S. 137-142 
    ISSN: 1434-3916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mechanical performance and the stress shielding effects of the Howmedica Spherolock MKII implant were evaluated. Three types of stable proximal femoral fractures were created in composite femurs and fixed with the nail-plate. The femurs were loaded to failure, and the yield strength, stiffness, and failure modes were noted. Additional intact composite femurs were fitted proximally with strain gauges, and the strain was examined under load. The femurs then underwent intertrochanteric fracture, plating, and re-testing. Comparative analysis showed that while the Spherolock system is less strong and stiff than other commonly used implants, it provides excellent and uniform load transfer across the fracture site. Varus rotation of the femoral head under load tended to open the fracture gap and localize the resultant load medially. Stress shielding of the calcar was less than 25% of the applied load even in the worst case. This very low stress shielding behavior was attributed mainly to the implant’s low stiffness.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Archives of orthopaedic and trauma surgery 116 (1997), S. 137-142 
    ISSN: 1434-3916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mechanical performance and the stress shielding effects of the Howmedica Spherolock MKII implant were evaluated. Three types of stable proximal femoral fractures were created in composite femurs and fixed with the nail-plate. The femurs were loaded to failure, and the yield strength, stiffness, and failure modes were noted. Additional intact composite femurs were fitted proximally with strain gauges, and the strain was examined under load. The femurs then underwent intertrochanteric fracture, plating, and re-testing. Comparative analysis showed that while the Spherolock system is less strong and stiff than other commonly used implants, it provides excellent and uniform load transfer across the fracture site. Varus rotation of the femoral head under load tended to open the fracture gap and localize the resultant load medially. Stress shielding of the calcar was less than 25% of the applied load even in the worst case. This very low stress shielding behavior was attributed mainly to the implant's low stiffness.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1996), S. 149-152 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Bone remodelling of the proximal femur following total hip arthroplasty (THA) is related to stress deviation with respect to physiological condition. The clinical relevance of this process is much debated with respect to its role in THA failure. In the present study a group of 475 An.C.A. anatomic cementless stems implanted in our institution were assumed as clinical reference. Of them, 294 had a short stem and 181 had a long stem. Stress shielding was X-ray evaluated in each patient. The survivorship analysis of this study group (negative events = stress shielding) showed significantly (p〈0.05) lower survival rates at 25 months follow-up for patients with long-stem implants. A 3-D FEM model of the proximal femur was used to analyse the load transfer mechanism for the two types of stems in fully or proximally only bonding conditions. Little difference was predicted in the proximal stress magnitudes for the different stem lengths. On the contrary, stem-bone bonding leads to a notable increase in the stress shielding.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Experimental mechanics 37 (1997), S. 350-354 
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A major problem of hip prostheses and other bone fixation devices is that they alter the stress distribution in the femur. This phenomenon is named stress shielding, and derives from the bigger stiffness of the implant when compared to the bone. Strain gages are the most common tool used in in vitro stress-shielding investigations. There is a lack of agreement in the literature about which gage type is to be preferred (uniaxial grid, biaxial or triaxial rosette). Rosettes are required when complete information is needed. However, uniaxial gages can be advantageous because they reduce the number of measurement channels required. The aim of this work is to verify if (and under which hypothesis) uniaxial gages can replace triaxial rosettes.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 30 (1996), S. 181-186 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: An accelerated cyclic loading corrosion test was used to determine the corrosion behavior of a commercial (GSP) and a prototype titanium hip prosthesis each with a modular neck. Four GSP and four prototype stems were subjected to a 2-Hz cyclic load ranging between 200 and 2,100 N for 1,000,000 cycles. Three stems were tested in an environment of FeCl3 solution, three stems were tested in Ringer's solution, and two stems were tested in air. After cyclic loading, the specimens were carefully examined with optical and scanning electron microscopy (SEM). None of them showed macroscopic or microscopic signs of corrosion, regardless of the environment to which the specimens were subjected. However, macroscopic evidence of mechanical fretting was present at the neck-stem modular junction, primarily concentrated at the medial contact point between stem and neck, especially for the prototype stems. SEM analysis confirmed these observations. The appreciable differences observed between the two designs suggest that the problem can be minimized or eliminated with an accurately designed taper fitting. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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