Arkady S. Voloshin

A METHOD TO PRODUCE UNIFORM PLANE-STRESS STATES WITH APPLICATIONS TO FIBER-REINFORCED MATERIALS

This work is concerned with a new method for testing material properties under uniform plane-stress conditions by means of a specially designed plane specimen. Photoelastic analysis showed that in the significant section of the specimen it is possible to produce uniform plane stress, with high accuracy, subject to the limitation that the principal stresses are of different signs. An important special case of loading produces pure shear on the significant section. The specimen is of particular importance for fiber-composite testing.The experimental results presented are encouraging.

Shock absorption of meniscectomized and painful knees: A comparative in vivo study☆

The principles of a noninvasive measurement of the shock absorbing capacity of the knee are presented. Accelerometry, which has been proven to be a useful tool for noninvasive measurements in biomechanical investigation, was employed for quantitative evaluation of the knees shock absorbing capacity by registration of bone vibrations resulting from the gait. Results of the experiments show that both patients with painful knee and patients after meniscectomy suffer from insufficient shock absorbing capacity of the knee. It was found that the shock absorbing capacity of a normal knee is about 20% higher than that of a pathological one. The results indicate that while meniscectomy may reduce pain, instability, swelling, etc. in an injured knee, it cannot improve its reduced shock absorbing capacity, which eventually will lead to development of degenerative osteoarthritis. It seems that the pain syndrome is a biological reaction to severe repetitive overloading of the knee. Noninvasive in vivo determination of the knees shock absorbing properties may be useful as an additional clinical technique to reveal a knees pathology. It may lead to early discovery of knee insufficiency, so that preventive steps can be taken to delay or reverse the process of degeneration.

An in vivo study of low back pain and shock absorption in the human locomotor system

In this second of three papers, the principles of a non-invasive in vivo method to quantitatively evaluate the shock absorbing capacity of the human musculoskeletal system and the correlation of this shock absorbing capacity with low back pain (LPB) symptoms are presented. The experiments involved patients suffering from low back pain (as well as other degenerative joint diseases) and healthy patients. The obtained results reveal that low back pain correlates with the reduced capacity of the human musculoskeletal system between the femoral condyle and the forehead to attenuate incoming shock waves. Examination of the absolute values of the amplitude of the propagated waves leads to the conclusion that the human locomotor system, which possesses reduced attenuation capacity, tries to prevent overloading of the head from insufficiently attenuated shock waves. Results of the present investigation support the idea that the repetitive loading resulting from gait generates intermittent waves that propagate through the entire human musculoskeletal system from the heel up to the head. These waves are gradually attenuated along this course by the natural shock absorbers (bone and soft tissues). Contemporary methods for examination of the human musculoskeletal system may by improved by using the proposed non-invasive in vivo technique for quantitative characterization of the locomotor systems shock absorbing capacity.

Force Wave Transmission Through the Human Locomotor System

A method to measure the capability of the human shock absorber system to attenuate input dynamic loading during the gait is presented. The experiments were carried out with two groups: healthy subjects and subjects with various pathological conditions. The results of the experiments show a considerable difference in the capability of each groups shock absorbers to attenuate force transmitted through the locomotor system. Comparison shows that healthy subjects definitely possess a more efficient shock-absorbing capacity than do those subjects with joint disorders. Presented results show that degenerative changes in joints reduce their shock absorbing capacity, which leads to overloading of the next shock absorber in the locomotor system. So, the development of osteoarthritis may be expected to result from overloading of a shock absorbers functional capacity.

Half-fringe photoelasticity: A new approach to whole-field stress analysis

This paper presents a new method for whole-field stress analysis based on a symbiosis of two techniques—classical photoelasticity and modern digital image analysis. The resulting method is called ‘half-fringe photoelasticity (HFP)’.Classical photoelasticity demands materials with high birefringence, which leads to extensive use of plastics as model materials. Since the behavior of these materials is often different from that of the prototype materials, their use distorts the similitude relationships. In many contemporary problems this distortion is untenable. HFP offers a way out of this dilemma. It permits materials and loads to be chosen so that no more than one half of a fringe order appears in the area of interest. Thus, for example, glass, which behaves linearly up to high stress levels and over a wide range of temperatures, could be used as model material. Alternatively, models from polymeric materials could be used under very low load in order to stay within the linear part of the stress-strain diagram and to prevent large deformations. The half-fringe-photoelasticity system, which is described here, utilizes the resulting low levels of birefringence for effective stress analysis.This paper describes the system. It outlines a calibration routine and illustrates its application to two simple problems using glass models.

Role of plantar fascia in the load bearing capacity of the human foot

Plantar fascia release is an accepted and widely used surgical way to reduce heel pain, however its effect of the load bearing characteristics of the foot is not well studied. A simple biomechanical model is developed here to analyze load bearing mechanism of the foot during the stance phase of the gait cycle. Quasilinearization is used for the system identification, and all models parameters are determined from the in vivo tests. The model is used to compare the load bearing mechanism of different pathological situations. The results of the study suggest that the plantar fascia carries as much as 14% of the total load on the foot. Its surgical release decreases dynamic loading on the ankle by only 10%. It is also found that the lowering of the arch degenerates the load bearing capacity of the foot. Thus, the plantar fascia plays an important part in the load bearing by the foot and its surgical release should be carefully considered.

Dynamic loading on the human musculoskeletal system —effect of fatigue

OBJECTIVE: A study was conducted to investigate the effects of fatigue on the ability of human musculoskeletal system to deal with the onslaught of the heel strike initiated shock waves. DESIGN: Running on a treadmill at the anaerobic threshold level for 30 min was used to acquire the experimental data on the foot strike initiated shock waves. BACKGROUND: Muscles act to lower the bending stress on bone and to attenuate the dynamic load on human musculoskeletal system. Fatigue may diminish their ability to dissipate and attenuate loading on the system. Knowledge of the effects of fatigue on the ability of the human musculoskeletal system to attenuate the shock waves may help in design of the training procedures and exercises. METHODS: Twenty-two young healthy males participated in this study. Each one was running on the treadmill at the speed corresponding to his anaerobic threshold for 30 min. The heel strike induced shock waves were recorded every 5 min on the tibial tuberosity and sacrum. The data obtained were analyzed in both temporal and frequency domains. RESULTS: The results reveal significant increase in the dynamic loading experienced by the human musculoskeletal system with fatigue. This may be attributed to the inability of the fatigued system to provide an efficient way to attenuate shock waves. CONCLUSIONS: The analysis of the recorded signals suggests that fatigue contributes to the reduction of the human musculoskeletal systems capacity to attenuate and dissipate those shock waves. This capacity appears to be a function not only of the fatigue level, but also of the vertical location along the skeleton. RELEVANCE: Fatigue during running may affect the ability of the human musculoskeletal system to attenuate and dissipate the heel strike induced shock waves. The study of the fatigue effect on shock wave attenuation provides information that may benefit the runner.

Influence of Artificial Shock Absorbers on Human Gait

The effect of artificial shock absorbers on the human gait and the technique for its quantitative evaluation have been studied. The results obtained have shown that viscoelastic inserts reduced the amplitude of the incoming shock waves bearing upon the musculoskeletal system as a result of the heel strike, by 42 percent (mean value). Conservative treatment, using such inserts for patients with different clinical symptoms of degenerative joint diseases, has shown excellent results. Seventy-eight percent of the clinical symptoms disappeared, while satisfactory improvement was reported in 17 percent of the subjects.

Shock Transmission and Fatigue in Human Running

The goal of this research was to analyze the effects of fatigue on the shock waves generated by foot strike. Twenty-two subjects were instrumented with an externally attached, lightweight accelerometer placed over the tibial tuberosity. The subjects ran on a treadmill for 30 min at a speed near their anaerobic threshold. Fatigue was established when the end-tidal CO2 pressure decreased. The results indicated that approximately half of the subjects reached the fatigue state toward the end of the test. Whenever fatigue occurred, the peak acceleration was found to increase. It was thus concluded that there is a clear association between fatigue and increased heel strike-induced shock waves. These results have a significant implication for the etiology of running injuries, since shock wave attenuation has been previously reported to play an important role in preventing such injuries.

Cyclic impacts on heel strike: A possible biomechanical factor in the etiology of degenerative disease of the human locomotor system

SummaryThe cyclic impacts induced by heel strike when walking were studied using both a high-resonance-frequency force plate and a low-mass skin-mounted accelerometer. The data were computer analyzed. The results showed that during normal human walking, the locomotor system is subjected to repetitive impact loads at heel strike, lasting about 5 ms and consisting of frequency spectra up to and above 100 Hz. The natural shock-absorbing structures in the musculoskeletal system have viscoelastic time-dependent mechanical behavior, which is relatively ineffective in withstanding sudden impulsive loads. Degenerative joint diseases may thus be seen as a late clinical result of fatigue failure of the natural shock absorbers, submitted to deleterious impacts over a period of time.