Fatigue crack growth rate does not depend on mantle thickness: an idealized cemented stem construct under torsional loading

Predicting fatigue crack growth rates and thresholds at low temperatures

The crack growth characteristics of a 4-ply, unidirectional, titanium matrix composite, SCS-6/Ti-6Al-2Sn-4Zr-2Mo, subjected to thermomechanical fatigue were investigated. A linear summation model was developed to predict the isothermal and thermomechanical fatigue (TMF) crack growth rates of the composite. The linear summation approach assumes the total fatigue crack growth rate is a combination of a cycle-dependent and a time-dependent component. To assist the modeling effort, a series of isothermal, in-phase, and out-of-phase crack growth tests were conducted. The test temperatures ranged from 150‡C to 538‡C and the fastest thermal frequency was 0.0083 Hz. With the exception of the 150‡C isothermal test, the model was able to correlate all the baseline fatigue crack growth test data between δK of 50 to 90 MPa √m. In addition, the model was able to predict the fatigue crack growth rate of a proof test which involved a continual change in temperature range and load range to produce a constant crack growth rate. The proof test began under isothermal conditions at the maximum temperature and ended under in-phase TMF conditions.

Stem cement debonding is 1 of the most common forms of fixation failure and is thought to be a prelude to gross loosening of a total hip reconstruction. However, the immediate consequences of debonding remains a matter of controversy. The dynamic effects of stem cement debonding in total hip reconstruction were analyzed using 3-dimensional finite element techniques. Stem cement interface conditions were assumed as completely bonded or unbonded, with or without friction. The dynamic effects were accounted for, as presented by the stance and swing phases of the gait cycle. It was found that both cyclic micromotions at the stem cement interface and stresses in the cement mantle were effectively reduced by friction. The friction cases produced failure probabilities of the cement mantle that were relatively close to the one generated by the bonded stem. The probability of mechanical failure of the cement bone interface decreased after debonding and decreased more with reduced stem cement friction. These results show that, although a firm and lasting bond between stem and cement may be desirable for preventing cement failure, the mechanical effects of a debonded stem are less detrimental than were assumed earlier. For straight tapered stem shapes subjected to the loading conditions described, a polished stem may be desirable for the cement bone interface mechanics.

The influence of cement mantle thickness and stem geometry on fatigue damage in two different cemented hip femoral prostheses

In this study, the fatigue crack growth (FCG) characteristics of the short surface crack was studied at various stress ratios, R, using the fine grained cemented carbide. The FCG law for the material was studied using two parameters, the maximum stress intensity factor Kmax and the stress intensity factor range ΔK. It was found that the relationship between the rate of FCG, da/dN and ΔK depends on the R value. In the da/dN vs. Kmax relation, at the region of high crack growth rate, the FCG rate was nearly constant by the value of Kmax without depending on R. However, in the low FCG rate region, the FCG rate tended to accelerate as R became lower. Therefore, it was difficult to specify da/dN as a single value at different R ratios using either ΔK or Kmax from the low speed region to the high-speed region. For that reason, the FCG behaviour of the material was studied based on the crack growth law, da/dN = AKmaxmΔKn. The values of m and n were obtained as 6.6 and 1.4, respectively. Therefore, it was found that the FCG rate of the cemented carbide was strongly dependent on Kmax rather than ΔK, like the FCG characteristics of ceramics.

Retrieval studies suggest that the loosening process of the cemented femoral components of total hip arthroplasties is initiated by failure of the bond between the prosthesis and the cement mantle. Finite element (FE) analyses have demonstrated that stem–cement debonding has stress-producing effects in the cement mantle. High interface friction, which corresponds to a degree of surface roughness, reduces these stresses. In experiments, however, debonded rough stems produced more cement damage than polished ones; in the Swedish Hip Register polished stems were clinically superior with respect to stems with a mat surface finish. The purpose of the present study was to investigate this contradiction. For this purpose, global and local FE models with debonded stem–cement interfaces were used to study the effects of prosthesis surface roughness on the cement stresses on a global scale and microscale, respectively. Similar to earlier numerical studies, the global FE model predicted that an increased surface roughness of the stem reduced the stresses in the cement mantle. The local model provided insight in the load-transfer mechanism on a microscale and could explain the experimental and clinical findings. The local cement peak stresses around the asperities of the surface roughness profile increased with increasing surface roughness and decreased again beyond a particular roughness value. Cement abrasion is caused by localized stresses in combination with micromotion. From this study it can be concluded that to minimize cement abrasion, debonded stems should either have a polished microstructure to minimize the local cement stresses or have a profiled macrostructure to minimize micromotions at the stem–cement interface. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 554–559, 1998.

Modeling of I + II mixed mode crack initiation and growth from the notch

Role of prism decussation on fatigue crack growth and fracture of human enamel

High thermally loaded construction exploitation practice has shown that the destruction under the loading with the temperature field caused by a moving heat source can be much more dangerous than the one in case of a stationary heat source. The growth of long cracks in the first case occurs by means of the two main mechanisms specific to the describing loading conditions. They are the codirectional crack growth mechanism when a crack grows jointly with the thermal tension stresses zone and the oppositely directional mechanism realizing when a crack grows in the opposite direction relative to the stress field moving direction. In both cases, the ultimate crack extension will be limited only by the stress moving zone. However, an experimental proof of such a crack growth on ductile specimens was absent. To demonstrate the possibility of crack development under the action of the moving temperature field up to the length essentially greater than the temperature stress tension zone by the mechanisms peculiar to such loading, the experiment on steel thin-walled cylinder was carried out. The specimens were heated in the circular high-frequency current inductor. Cold-water jet falling on the specimen’s surface resulted in high temperature gradients and high local stresses. Automodel movement of the temperature field was achieved by means of the drive rotating the specimen about its longitudinal axis. The fatigue crack arose under the action of cyclically moving temperature field. Thereafter, the near-automodel fatigue crack growth proceeded. After several tens of cycles, the crack length essentially exceeded the thermal tension zone and became greater than half-circumference. The experimentally obtained crack growth rate was in good agreement with the calculated result by the developed calculation technique. It was proved that in addition to the codirectional and oppositely directional quasistatic mechanisms, the high-speed fatigue crack growth is also possible in constructions made of materials having a considerable fracture toughness. It can occur in the same and opposite directions relative to the temperature field moving direction. Although the fatigue crack growth rate is small in comparison with the quasistatic codirectional and opposite directional ones, the final crack length can also reach a great size. That length is limited only by the tensile stress moving region.

Bone creep and short and long term subsidence after cemented stem total hip arthroplasty (THA)

PurposeThis study aims to investigate the reliability issues of microvoid cracks in solder joint packages exposed to thermal cycling fatigue.Design/methodology/approachThe specimens are subjected to JEDEC preconditioning level 1 (85 °C/85%RH/168 h) with five times reflow at 270°C. This is followed by thermal cycling from 0°C to 100°C, per IPC-7351B standards. The specimens' cross-sections are inspected for crack growth and propagation under backscattered scanning electronic microscopy. The decoupled thermomechanical simulation technique is applied to investigate the thermal fatigue behavior. The impacts of crack length on the stress and fatigue behavior of the package are investigated.FindingsCracks are initiated from the ball grid array corner of the solder joint, propagating through the transverse section of the solder ball. The crack growth increases continuously up to 0.25-mm crack length, then slows down afterward. The J-integral and stress intensity factor (SIF) values at the crack tip decrease with increased crack length. Before 0.15-mm crack length, J-integral and SIF reduce slightly with crack length and are comparatively higher, resulting in a rapid increase in crack mouth opening displacement (CMOD). Beyond 0.25-mm crack length, the values significantly decline, that there is not much possibility of crack growth, resulting in a negligible change in CMOD value. This explains the crack growth arrest obtained after 0.25-mm crack length.Practical implicationsThis work's contribution is expected to reduce the additional manufacturing cost and lead time incurred in investigating reliability issues in solder joints.Originality/valueThe work investigates crack propagation mechanisms of microvoid cracks in solder joints exposed to moisture and thermal fatigue, which is still limited in the literature. The parametric variation of the crack length on stress and fatigue characteristics of solder joints, which has never been conducted, is also studied.

Modeling of temperature influence on the fatigue crack growth behavior of superalloys

The fracture of restored teeth is a significant obstacle to lifelong oral health. Recent studies suggest that fatigue cracks originate at flaws introduced during cavity preparation and that fatigue crack growth is a principle cause of restored tooth fractures. In this study, the rate of fatigue crack growth in bovine dentin was estimated under mode I cyclic loading. Double cantilever beam (DCB) specimens were obtained from bovine molars and subjected to high cycle fatigue loading (10(5) < N < 10(6)). The fatigue crack growth rates were measured and used to estimate the crack growth exponent and coefficient according to the Paris Law. The average fatigue crack growth exponent was 4.7 +/- 0.6 for crack growth parallel to the dentin tubules, which was significantly larger than 4.3 +/- 0.5 for crack growth perpendicular to the tubules (t-test, CI > 80%). Although the crack growth rates varied considerably, there was no significant dependence on tubule orientation or tubule density. However, specific features of the fracture surfaces and tendencies for crack curving away from the tubules suggested preferential fatigue crack growth perpendicular to the dentin tubules. Results from this study are being used to guide an experimental investigation of fatigue crack growth in human dentin.

A unified description of mechanical and actuation fatigue crack growth in shape memory alloys

The fatigue crack growth behavior in butt-welded joints of STS42 steel was examined using compact type (CT), center-cracked tension (CCT) and single edge cracked (SEC) specimens, and the effects of specimen configuration, thickness, crack orientation and location of weld line in the specimens on the fatigue crack growth rate in the welded joints were examined in connection with welding residual stress.The fatigue crack growth rate in the CCT specimen was similar to or slightly higher than that in the base metal, whereas the crack growth rate in the CT or SEC specimen decreased considerably as compared with that in the CCT specimen, except for the CT specimen with a notch on the weld line. The crack growth rate increased slightly with increasing specimen thickness, regardless of specimen configuration. In the case of the CT specimen with perpendicular crack orientation with respect to the weld line, the crack lengths of the both sides of the specimen surface were often different each other. The side with an advanced crack front corresponded to the backing side with finishing pass. When a crack existed within the region of initial compressive residual stress field, the overall distribution of residual stress did not change appreciably. The effect of welding residual stress on the crack growth rate was the same as that of stress ratio on the growth rate of the base metal. The crack growth rate in the welded joints was correlated with the effective stress intensity factor range, ΔKeffR, which was estimated by superposition of the respective stress intensity factors for the residual stress field and for the applied stress, regardless of specimen configuration and distribution of residual stress in the specimens.