Modelling fatigue of bone cement

Accurate models of cement and interface fatigue are essential if computationally assessing risk of aseptic loosening of cemented joint replacements is to become clinically relevant. A series of approaches will be presented that attempt to model several aspects of bone cement fatigue relevant to predicting cemented joint replacement failure. Failure models for homogeneous (bulk) bone cement and its interface with implant and host tissue are reviewed. Variability introduced by porosity and interaction between fatigue and creep are also considered. Finally, some current and potential future developments are discussed.

Post-tensioning glulam timber beams with basalt FRP tendons

Improvements in the structural performance of glulam timber beams by the inclusion of reinforcing materials can increase both the service performance and ultimate capacity. This paper describes a series of four-point bending tests conducted, under service loads and to failure, on unreinforced, reinforced and post-tensioned glulam timber beams, where the reinforcing tendon used is 12 mm dia. basalt fibre-reinforced polymer. The research is designed to evaluate the benefits offered by including an active reinforcement in contrast to the passive reinforcement typically used within timber strengthening works, in addition to establishing the effect that bonding the reinforcing tendon has on the material's performance. Further experimental tests have also been developed to investigate the long-term implications of this research, with emphasis placed upon creep and loss of post-tensioning; however, this is ongoing and is not presented in this paper. The laboratory investigations establish that the flexural strength and stiffness increase for both the unbonded and bonded post-tensioned timbers compared to the unreinforced and reinforced beams. Timber that is post-tensioned with an unbonded basalt fibre-reinforced polymer tendon shows a flexural strength increase of 2ṡ8% and an increase in stiffness of 8ṡ7%. Post-tensioned beams with a bonded basalt fibre-reinforced polymer tendon show increases in flexural strength and stiffness of 15ṡ4% and 11ṡ5% respectively.

Development of Novel Post-Tensioned Glulam Timber Composites

Improvements in the structural performance of glulam timber beams by the inclusion of reinforcing materials can increase both the service performance and ultimate capacity. In recent years research focusing on the addition of fibre reinforced polymers (FRP) to strengthen members has yielded positive results. However, the FRP material is still relatively expensive and its full potential in combination with structural timber has not been realised. This paper describes a series of four-point bending tests that were conducted, under service loads and to failure, on unreinforced, reinforced and post-tensioned glulam timber beams, where the reinforcing tendon used was 12mm diameter basalt fibre reinforced polymer (BFRP). The research was designed to evaluate the benefits offered by including an active reinforcement in contrast to the passive reinforcement typically used within timber strengthening works, in addition to establishing the affect that bonding the reinforcing tendon has on the material’s performance. Further experimental tests have been developed to investigate the long-term implications of this research, with emphasis placed upon creep and loss of post-tensioning.
The laboratory investigations established that the flexural strength and stiffness increased for both the unbonded and bonded post-tensioned timbers compared to the unreinforced beams. Timber that was post-tensioned with an unbonded BFRP tendon showed a flexural strength increase of 2.8% and an increase in stiffness of 8.7%. Post-tensioned beams with a bonded BFRP tendon showed increases in flexural strength and stiffness of 16.6% and 11.5% respectively.

Strength reduction of till under dynamic pore pressure condition

Cuttings in heavily overconsolidated clays are known to be susceptible to progressive deformation caused by creep and fatigue that usually begins at the toe of the slope. The progressive deformation leads to strength reduction with time at constant stress (or called softening) and could be accelerated by fluctuation of groundwater level associated with more extreme rainfall events predicted through climate change. The purpose of this paper is to assess the mechanism of progressive deformation due to creep and fatigue using element testing on samples of till. The samples were subjected to fully drained loading and the deviator stresses were held constant at various percentages of peak failure stress, while the pore water pressure was kept static or dynamic (fluctuating ±5 kPa) over a period of time. The results have shown that the samples experienced significant deformation even at a higher factor of safety (i.e. the failure deviator stress/deviator stress at which the pore water pressure was fluctuated) under pore water pressure dynamics.