Check out our FAQs. This standard has been revised by ISO Abstract ISO specifies procedures for static and cyclic strength tests on lower-limb prostheses where, with one exception, compound loadings are produced by the application of a single test force. The tests described in ISO comprise: principal static and cyclic tests for all components; a separate static test in torsion for all components; separate static and cyclic tests on ankle-foot devices and foot units for all ankle-foot devices as single components including ankle units or ankle attachments and all foot units as single components; a separate static ultimate strength test in maximum knee flexion on knee joints and associated parts for all knee units or knee-shin-assemblies and adjacent components that normally provide the flexion stop on a complete prosthesis; separate static and cyclic tests on knee locks for all mechanisms which lock the knee joint in the extended position of the knee unit or knee-shin-assembly.
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CHF Buy. Life cycle Previously Withdrawn. Final text received or FDIS registered for formal approval. Proof sent to secretariat or FDIS ballot initiated: 8 weeks. Close of voting. In this study the mechanical compressive tests, which based on that outlined in ISO were performed.
The force-deflection responses were described in two regions. The initial, was the linear part of the force-deflection curve and denoted as the initial stiffness S1 , while the nonlinear part for the rest of curve up to a design load was denoted as S2.
A third value Sh was also taken as the average stiffness between the no load and the design load in the curve. Ibrahem values were needed to accurately describe the non-linear mechanical behavior of the feet, [21]. Few studies have considered the use of FE analysis technique in evaluating the mechanical behavior of prosthetic feet [6, 15, 20]. A study comprising mechanical tests as that proposed by ISO were performed on a J-shape foot model [6].
These tests were then emulated using the FE analysis. Stiffness results by either the experiments or the FE curves were allocated as linear stiffness. This study illustrated that the FE analysis of the forefoot loading were matching with those obtained by the mechanical testing.
For the purpose of investigating repeatability of the mechanical tests on the prosthetic feet, a study on a Niagara foot model involved FE modeling were conducted [20]. In this study, the stiffness of foot were described by considering three different values K1, K2 and KH. The value K1 was corresponding to be the slope of the force- displacement curve from the starting zero load up to an elbow point. While, K2 was corresponding to the slope of the curve from the elbow up to N load, and KH was corresponding to the slope of the line from zero to N loads.
A methodology for evaluating the mechanical properties of the prosthetic feet was conducted through applying mechanical loads at different angles on the heel and the toe portions of the feet [14]. These loads were extracted from the waveform of the ISO Another numerical study, using FEA, on a novel design of a Dynamic Energy Return prosthetic foot, based on applying this methodology, was conducted. Although many of researchers [3, 4, 6, ] followed the ISO in performing mechanical tests on different types of prosthetic feet.
They did not evaluated stiffness by the same way. It seemed from their studies that, no standard method was followed in evaluating the structural stiffness of the prosthetic feet and so a more controlled approach is still needed in prescribing the prosthetic feet stiffness [21].
Although the proposed methodology was based on simulating mechanical testing as that prescribed by the ISO [14]. The stiffness was determined from the force-displacement curve at predetermined fixed levels of loading. Such methodology can be applied for evaluation and comparison purposes of different prosthetic feet designs.
In this study the methodology was applied to study the effects of thickness of the S-shape and material variations on the stiffness of a modified model of Niagara foot.
These stages were performed considering two different regimes of loading which were based on using either the standards ISO or ISO These stages consisted of creating a the prosthetic foot shape model, selecting its material, setting up the boundary conditions of loading, and performing analysis of the FE test results. The results were compared with that pronounced by Schmitz [20].
Ibrahem 2. In order to study the effect of material on the stiffness of prosthetic foot, Hytrel was selected to represent another type of material for only the four modified models M1 to M4. Both the Delrin l00P and the Hytrel were generally used in different studies [14, 20]. A summary of the mechanical properties of such materials is shown in Table 1. Table 1. The boundary conditions of these tests were set as that described by the ISO Where the loading was applied through displacing a virtual platen against the heel and the toe portions separately, at two different angles, Fig.
The tests were carried out on each of the four modified foot models M1 to M4 and on the original Niagara foot model NF , where the results of these tests were compared with that obtained in [20]. Ibrahem Fig. The platform of the foot was set to be fixed immovable in the x, y and z directions Fig. Contact settings between the platen and either the heel or the toe surfaces were adopted as frictionless without penetration.
The prosthetic foot was set to be self-interacted, since it had a special design, that it contained prongs. Another boundary condition for the type of contact between the two prongs and the opposite face was also managed. Such contact was arranged to be surface to surface frictionless contact without penetration, Fig.
A coordinating system was also created on the platen in order to control its movement, where remote displacements of the platen were generated to provide loads on the heel and toe modes of loading.
Meshing is a crucial step in the design analysis. The SolidWorks program automatically assigns the appropriate mesh type to the object based on its geometry features. It created a solid mesh with tetrahedral solid elements in the foot solid shape, Fig.
For all proposed models of the foot, the SolidWorks assigned different sizes of elements ranged between 6. These values were readjusted to be 5 mm for all the models. Table 2 shows the total nodes and elements for the original NF and the four modified models.
The models were represented by two different materials Delrin l00P and Hytrel All feet were subjected to loading conditions conformed to that prescribed by the ISO The values of forces as well as their corresponding directions were simulating the expected vertical ground reaction loads on the foot P4 loading curve that could be occurring during the stance period of gait msec.
Two methods were deduced for describing stiffness of the toe and heel portions of the Niagara foot. The first method, considered the stiffness values K1, K2 and KH [20]. The second method, approximated the data of the force-displacement using least square method to obtain a mathematical model. The mathematical expression describing the load-displacement relationship, was tested by applying polynomial functions of 2nd up to 6th order.
Stiffness were determined mathematically, as the slope of the force- displacement function at four different selected foot loads N, N, N and N.
The first was based on the ISO standard. The load-displacement data obtained from the FEA were interrelated by two different prescribed methods. The second was based on the ISO- standard. Stiffness progressively increased up to the end of loading. An elbow point, on the curve, was noticed at about 2.
After this displacement, stiffness of the toe exhibited rapid increase, which attributes to the closing of the gap between the prongs and keel as shown in Fig.
Consequently, the measure of this gap was expected to affect the location of the elbow point. The maximum reached load N , was corresponding to The data about the Force-displacement relationship were firstly modeled as a 4th order polynomial function, this differentiated to determine the stiffness values slopes of the curve were corresponding to the pre- specified loads, N, N, N and N. Such values were Ibrahem 3.
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