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The first objective of this study was to design a hip protector that would effectively attenuate and shunt away from the greater trochanter the impact energies created in typical falls of the elderly. As the shock absorption material, the protector included the 12 mm-thick Plastazote, which was found to be the most efficient energy-absorbing material in our previous in vitro biomechanical tests. With an anatomically designed semiflexible outer shield of the protector (high density polyethylene), the impact surface was increased and the impact energy shunted away from the greater trochanter. In the second phase of the study, we determined the force attenuation capacity of this device in realistic (in vitro) falling conditions of the elderly. With the impact force of 6940 N used (a typical hip impact force measured in in vitro falling tests), the trochanteric soft tissue (25 mm-thick polyethylene foam) attenuated the peak femoral impact force to 5590 N and the tested protector to 1040 N. In the second series of this experiment, the peak femoral impact force was set to be so high (13,130 N) that the protector, if effective, should prevent the hip fracture in almost all cases. The trochanteric soft tissue attenuated this peak impact force to 10,400 N and the tested protector to 1810 N. Thus, the force received by the proximal femur still remained clearly below 4170 N, the average force required to fracture in vitro the proximal femur of the elderly in a fall loading configuration. In conclusion, our test results suggest that an anatomically designed energy-shunting and energy-absorbing hip protector can provide an effective impact force attenuation in typical falling conditions of the elderly. However, the efficacy of the protector in the prevention of hip fractures can only be evaluated in randomized clinical trials.

The purpose of this study was to determine and compare the force attenuation properties of various external trochanteric padding materials under in vitro conditions simulating characteristic falling of the elderly. The selected materials had to be practically suitable for external hip padding so that the main criteria for the materials were good energy absorbing capacity, good durability, low weight, good recovery after compression, easy availability, and reasonable price. Eight materials met these requirements. The first six were flexible cross-linked polyethylene foams with densities from 30 to 200 kg/m3. The seventh material was Plastazote polyethylene foam, and the eight foam was made of ethylene-vinyl acetate (EVA) copolymer. With a pendulum effective mass of 39 kg, impact velocity of 3.0 m/s, and impact force of 8.2 kN, the force attenuation provided by the 20 mm thick hip-padding materials was quite small, ranging from 22 to 38%. With all these materials the peak femoral force remained above 5 kN, more than two times above the femoral fracture threshold (2 kN). In the second set of experiments, the impact force was gradually reduced until the tested materials lowered the impact force below the fracture threshold. With the most efficient material this critical falling velocity was found to be 1.6 m/s. To go below the fracture threshold with the realistic impact velocity of 3.0 m/s, the padding materials had to be 100-140 mm thick.(ABSTRACT TRUNCATED AT 250 WORDS)

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This study represents the first measures and experiences of using an external hip protector in humans under forces that could, without the protector, fracture the proximal femur of some of the elderly persons. In other words, we wanted to know if it is possible, using the hip protector, to hit the proximal femur of young volunteers with forces that have the power to fracture some individuals' proximal femur, and if so, how intense is the pain reaction under the impacted area? Four of the researchers (JP, AH, HS, and PK) volunteered to be the study subjects. In the impact experiments, we wore the protector on both sides of the pelvis (greater trochanter), and the pendulum, with an effective mass of 40 kg, was impacted on the protector. The descent height was gradually increased and the highest impact energy used was 115 J. With a load cell mounted on the head of the pendulum we ensured that the external forces used were high enough to fracture the proximal femur of some of the elderly people. Using the external hip protector we tolerated the impacts well although after the high energy impacts every subject reported mild tenderness on the skin area under the contact surface of the protector. Repeated examinations of the impacted area of the study subjects did not reveal hematoma or swelling. In conclusion, our test results suggested that, when wearing an anatomically designed energy-shunting and energy-absorbing hip protector, the fall-induced peak impact forces do not cause undue pain to the impacted hip region, and, in all probability, the forces entering into the proximal femur remain below the range of force capable of fracturing the proximal femur of the elderly. The protector was found to be comfortable to wear and it did not move (slip away) during the experiment. We feel that our protector is now ready for a feasibility study and then for a randomized clinical trial.

A laser clad and machined cylindrical structural steel rod was fatigue tested under four-point bending load. The resulting fracture could be tracked back to a spherical surface pore in the Co-based coating. Due to an oxide inclusion, the pore was not identified by dye penetrant inspection. Two circular buckling strain patterns that were detected beside the pore at the surfaces after fracture confirm local plastic deformation prior to crack initiation. In order to calculate the stress field around the surface pore, linear elastic finite element analysis was carried out. For four-point bending load, a surface pore generally exceeds the maximum stress of a smooth rod as long as the pore is located within an azimuthal angle of ±55°, which was the case for the presented as well as for another pore initiated sample.

Laser cladding is an overlay welding method to manufacture high performance, fusion bonded metal, and metal matrix composite coatings on metallic substrates with low dilution. Owing to steep thermal gradients, rapid solidification, and possible mismatch in coefficients of thermal expansion between the coating and the substrate, laser cladding induces large tensile residual stresses in coating layer, potentially affecting the service life of clad component under external load-induced stresses. In this study, four-point bending and torsion fatigue tests were conducted on relatively large round laser clad steel bars to determine the effect of laser cladding on fatigue strength. Quenched and tempered 42CrMo4 steel clad with Inconel 625 and S355 structural steel clad with Stellite 21 were subjected to various stress levels for relatively large number of cycles with and without postweld heat treatment (PWHT). The results indicated that Stellite 21 decreased the fatigue life of S355 at all the applied loads, whereas Inconel 625 increased the fatigue life of 42CrMo4 at high loads but decreased at low loads. Applied PWHT did not show any positive influence on fatigue life.

Summary. In this paper some preliminary results on the effect of plastic deformation on magnetic properties of an electric steel are presented. Both experimental results and modelling aspects are discussed.