PSI - Issue 28

Yuichi Otsuka et al. / Procedia Structural Integrity 28 (2020) 1018–1023 Y.Otsuka et al. / Structural Integrity Procedia 00 (2020) 000–000

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hip joints. The mechanisms of loosening an acetabular cup are classified as infectious disease, osteolysis, and aseptic loosening[2]. Though the e ff ects of infection or osterolysis on the aceptic loosening had been reported, the e ff ects of mechanical loading have not been clarified yet. Lewinnek et al. suggested “ safe zone ” concept that deviation in fixation angles of acetabular cups could a ff ect loosening behavior[3] and such the deviation was usually confirmed by X-ray observation[4]. The plasma-sprayed Hydroxyapatite (HAp) coating on the surface of the acetabular cups also has a risk of fracture by the mechanical loading[5, 6]. A clinical data base report warned that fracture of HAp coating may increase the loosening of th acetabular cup[7]. These reports challenged the e ff ectiveness of fixation e ff ect by HAp coating in long-term service. Our group previously developed an experiment system that can simulate loosen ing behavior assembled stem / acetabular cup components subjected to cyclic loading[8]. Their experimental work demonstrated that delamination of HAp coating, and the inelastic damages in surrounding porous composite material (simulated bone) could contribute the displacement of the acetabular cup. However, the individual contribution of each factor to the displacement behavior has not been experimentally unveiled yet. This study aims at experimentally clarifying the e ff ect of delamination of HAp coating and damages in porous com posite on the loosening behavior of acetabular cup separately. Delamination behavior of HAp coating can be observed using Acoustic Emission in situ. . Additionally, infrared measurement (IR) is newly installed to quantitatively observe the damage behavior of porous simulated bone during the cyclic loading test. Firstly, deformation behavior of porous simulated bone (alumina / polyurethane composite) by compressive loading was observed. Next, a combined measure ment using AE and IR was applied on damage evaluation of HAp coating as well as porous simulated bone during cyclic compression test. The degradation mechanism of the mechanical fixation force caused by both the damages and contributions on the loosening behavior of acetabular cup is discussed. The demension of artificial stem / cups was not commercial one but was originally designed by refering ISO7206, which was reported by our previous work[8]. The acetabular cup and stem were made of titanium alloy, Ti-6Al-4V ELI. The acetabular cup and stem were forged by Endo Manufacturing Company, Ltd, Japan. The thermal-sprayed powder was hydroxyapatite powder (HAP-100, Taihei Chemical Industrial Co., Ltd.). Atomspheric plasma spray process was applied to deposit HAp coating on the surface of aceetabular cups or stems. Porous simulated bone was fabricated by mixing alumina and polyurehane at the ratiof of 1:4. The porocity of the porous simulated bone was controlled by fabrication under a vacuum chamber in order to simulate the Young’s modulus of cancellous bone approximately at 100 MPa. The fabricated porous component was mechanically machined to the dimension of 30 × 30 × 30 mm 3 and then top and bottom surface ob the rectangular component was polished up to emery papers # 1000 in order to maintain uniform loading during the following compression test. 2.2. Compression tests of porous simulated bone Cyclic compression tests of the porous simualted bone were conducted in order to determine the damage behavior of the porous simualted bone itself. Loading was applied using a servo hydraulic fatigue testing machine ( load ca pacity 30kN, Shimadzu Corporations, Japan). Cyclic compression tests were conducted at stress ratio R = 10, f = 10Hz in a controlled atmospheric temperature of 20 ± 2 C ◦ using an air conditioner. Infrared Thermography camera(FLIR A6703c) was set on the front of the porous body and observed temperature change at the frequency of 1Hz. AE sensor (AE-900M,NF block ,co.ltd.,Japan) was also set on the bottom of fixation jig using a grease. Detected AE signals were amplified and filtered using preamp (AE-912, NF block ,co.ltd.,Japan) and discriminator(AE9922, NF block ,co.ltd.,Japan) . Total gain was 80dB with the threshold voltage of 0.2V, and HPF was 400kHz. Detected AE signals were also analyzed using FFT (labview) and clusterd using their maximum voltage and primal frequency. 2.3. Cyclic loading test to the acetabular cup 2. Experimental method 2.1. Fabrication of specimen and porous simulated bone

Figure 1 shows pictures of cyclic loading system with AE and IR measurement. . The cyclic loading conditions were a maximum compressive load of Pmax = -2.3kN with loading frequency of 10 Hz, refered by ISO7206. The