Viscous Criterion Research Articles

Relationship between the dynamic parameters and injury severity of chest subject to impact.

Seventeen dogs were subjected to blunt left lateral impact at velocities from 7.14 m/s to 19.05 m/s. The impacts to the thoracic wall were recorded by accelerometers fixed on the ribs at the impacted point and other areas. From this information the dynamic parameters (compression response, instantaneous deformation velocities, and viscous response) were calculated. The thoracic injury scores were recorded according to the Abbreviated Injury Scale (AIS-85). The results showed that the chest was a viscoelastic structure. The dynamic parameters of the chest wall were correlated with the physical parameters in exponential function or logarithmic function. There was a more significant relationship between viscous criterion and injury score among the various parameters. The relationship curve was sigmoid. The results indicated that the viscous response might be a valid parameter for indicating the severity of injury.

Pathologic study of thoracic impact injury involving a movable impact pattern.

The left thoracic walls of 28 rabbits were subjected to lateral blunt impact in a movable impact pattern. The impact velocities ranged from 7.95 m/s to 16.13 m/s, and the compression response ranged from 15.69% to 46.14% of the thoracic width. The surviving animals were sacrificed at 6 hours after trauma and were autopsied. Injury scores were assigned according to the hemorrhage area and the injury type (e.g., rupture or rib fracture). When compared with the pathologic characteristics of the thoracic injury involving a relatively static impact pattern, the severity of thoracic injury involving a movable impact pattern was milder. Also there were more significant differences in the severity of injury to lungs and ribs on the left as compared with the right sides. The viscous criterion is still a good parameter reflecting the severity of injury to lungs and heart. The severity of rib injury was mainly related to compression response.

Protection for Thorax Injury Severity in 90° Lateral Collision

The thoracic trauma index (TTI) and the viscous criterion (VC) are injury criteria intended for the prediction of torso injury severity. The criteria were assessed in two series of experiments: 90° (lateral) car to car collisions and controlled left trunk impacts against either a rigid or padded wall. Forty-two belt restrained human cadavers in the age range 18–65 years, located in the near-side front passenger seat, were used. The impact velocity was between 40 and 60 km/h. Left and right side impacts were simulated using standard or modified car side structures. With the second series of experiments, the left side of each subject was impacted under one of two different test conditions: 24 km/h rigid wall or 32 km/h padded wall. The thorax deformation was evaluated through the double integration of the accelerated difference at the fourth and eight ribs, near and far side. Deformation maxima of 6–138 mm (mean 69 mm), VC values of 0.3–4.7 m/s (mean 1.6 m/s), and TTI values of 85–252 (mean 63) occurred. Torso abbreviated injury severity (AIS) values were between 0 and 5. Statistical analyses showed a stronger influence of age on injury severity than the injury criteria or biomechanical responses in the two series of experiments. The TTI showed the highest correlation with thoracic AIS and the number of rib fractures, while VC was the better predictor of abdominal AIS. The results are discussed critically and the strength and robustness of the injury criteria analyzed.

Protection for Thorax Injury Severity in 90° Lateral Collision

The thoracic trauma index (TTI) and the viscous criterion (VC) are injury criteria intended for the prediction of torso injury severity. The criteria were assessed in two series of experiments: 90° (lateral) car to car collisions and controlled left trunk impacts against either a rigid or padded wall. Forty-two belt restrained human cadavers in the age range 18–65 years, located in the near-side front passenger seat, were used. The impact velocity was between 40 and 60 km/h. Left and right side impacts were simulated using standard or modified car side structures. With the second series of experiments, the left side of each subject was impacted under one of two different test conditions: 24 km/h rigid wall or 32 km/h padded wall. The thorax deformation was evaluated through the double integration of the accelerated difference at the fourth and eight ribs, near and far side. Deformation maxima of 6–138 mm (mean 69 mm), VC values of 0.3–4.7 m/s (mean 1.6 m/s), and TTI values of 85–252 (mean 63) occurred. Torso abbreviated injury severity (AIS) values were between 0 and 5. Statistical analyses showed a stronger influence of age on injury severity than the injury criteria or biomechanical responses in the two series of experiments. The TTI showed the highest correlation with thoracic AIS and the number of rib fractures, while VC was the better predictor of abdominal AIS. The results are discussed critically and the strength and robustness of the injury criteria analyzed.

Thoracic deformation and velocity analysis in frontal impact.

The objective of the present study was to measure dynamic chest deformations and compute chest velocity and viscous criterion during real world frontal impacts conducted on a horizontal sled. Four unembalmed human cadavers were restrained using a three-point belt restraint in the driver seat of a sled buck. Two chest bands (each with a 24 gauge capability) were placed on the thorax to record the temporal deformation patterns during impact. All tests were conducted at a velocity of approximately 50 kph. Biomechanical data were gathered digitally at a sampling rate of 12,500 Hz. Multiple rib fractures were identified in all specimens at autopsy. Analysis of approximately 800 temporal deformation contours of the thorax demonstrated regional differences. The overall mean maximum normalized chest deflections, maximum chest compression velocities, and peak viscous response variables ranged from 0.15 to 0.51, 1.79 to 4.87 m/s, and 0.15 to 1.95 m/s, respectively. These findings clearly illustrate the potential use of the chest band output to correlate injury with biomechanical variables and establish thoracic impact tolerance.

The Calculation of the Instability Criterion for a Uniform Viscous Flow Past an Oil Boom

An important problem in oil spill containment by booms is the instability of the oil-water interface at the boom. This instability, which represents the conditions under which oil can escape under the boom, is investigated. A viscous flow model for thin slicks in two dimensions is developed. To understand the effect of viscosity on the instability criterion, the full Navier-Stokes equations are solved by the fractional-step method in time-domain to determine the pressure gradients along the boom. The numerically obtained viscous instability criterion Analytical instability formulas for potential flows are based on the velocity potentials for attached and detached flows due to uniform current past a flat plate in finite and infinite water depths. The results show that the viscous flow model predicts a larger region of stability. It is numerically determined from the instability criterion that the oil droplets at the boom between the free surface and down to about 40 percent of the boom height can never escape, regardless of the current strength. It is also shown that the instability criterion depends weakly on the high Reynolds number. Reanalysis of the available experimental data confirms these findings.

A parametric study of the thoracic injury potential of basic taekwondo kicks.

A parametric investigation of the thoracic injury potential of basic taekwondo kicks was conducted through the use of computer simulations. Linkage-based models were employed to simulate the kinetics of the kicking leg and were used to drive a human thorax model. The results of the analysis according to the thoracic compression criterion indicated a minimal probability of severe injury (AIS4+) for swing kicks, nearly 0 percent and thrust kicks, less than three percent. The thoracic viscous criteria, on the other hand, predicted a severe injury probability of up to 100 percent for swing kicks and up to 80 percent for thrust kicks. Additional analysis showed that the injury potential was a strong function of the kick velocity and a weak function of the applied constant force. The injury potential was also found to be a weak function of the size and weight of the kicking leg, with variations in the peak compression and viscous response being typically below 5 percent for a 20 percent change in either the mass or the length.

Tolerance to Steering Wheel-Induced Lower Abdominal Injury

Anesthetized swine were tested for biomechanical and injury responses to lower abdominal steering wheel loading. The lower abdomens of 25 subjects were impacted with a segmented steering wheel. Tests included a wide spectrum of velocities, from 1.7 to 12.4 m/s, and forced abdominal compressions of 7.0%-54.5% of the vertical thickness of the lower abdomen. Lower abdominal injuries included contusions and lacerations of varying severity and frequency in the mesentery, the small and large bowel, the spleen, and the cecum. Logistic regression correlations were performed to assess the probability of severe and greater injury with biomechanical indices such as peak velocity of deformation (Vmax), peak compression (Cmax), peak total force (Fmax), the maximum Viscous criterion (VCmax), and the product of maximum total force and maximum compression (FmaxCmax). Although Cmax, Fmax, and, to a lesser extent, FmaxCmax correlated reasonably well with the probability of severe and greater injury, the maximum Viscous criterion (VCmax) was the best correlate, establishing VCmax as the most effective predictor of an AIS greater than or equal to 4 injury risk for steering wheel loading to the lower abdomen.

Thoracic injury potential of basic competition taekwondo kicks

A major concern in competition taekwondo is the injury potential posed by many of the powerful kicks used. An investigation of the kinetics of four kicks frequently used in competition was performed with high speed video. Velocities were measured, and energy was calculated. Typical values for basic swing kicks were 15 m s −1 and 200 J. Basic thrust kicks possessed 45% less velocity but 28% more energy than swing kicks. Linkage models were developed to simulate the motion and kinetics of the kicking leg. Injury potential was evaluated through thoracic compression and viscous criterion models. These models predict a significant probability of serious injury with all kicks, with thoracic deflections from 3 to 5 cm and peak viscous tolerance values from 0.9–1.4 m s −1, when no protective body equipment is used.

Analytical studies of injury criteria for the thorax.

The viscous criterion is a recently developed criterion to assess injury severity of the human thorax. In the viscous criterion, the peak viscous response, which is defined as the maximum product of deformation velocity and compression of an object, is proposed as a predictor of injury risk. However, the physical meaning of the criterion is not very clear. In this paper, the mathematical properties of the viscous criterion are analyzed. A mechanical thorax model is then used to relate the criterion to the physical quantities of the model using energy concepts. It is found that the so-called peak viscous response is strongly related to the peak energy storing rate of the thorax which is not related to the viscosity of the thorax. It is also shown that the viscous response of the thorax is given by the integral of the velocity squared with respect to time. The analysis is further expanded to a more general case to result in four criteria based upon the energy concepts. A hypothesis for injury assessment is proposed by using the four criteria.

A viscous tolerance criterion for soft tissue injury assessment

Experiments in our laboratory have documented that high-speed impact can cause severe injury to internal organs before either of the currently accepted chest injury criteria, which are based on spinal acceleration or chest compression, approach their tolerance limit. Those studies demonstrate an interdependence between the velocity of deformation and compression of the body on injury risk. A tolerable level of chest compression at a low velocity can prove to be fatal at higher velocities of deformation. The observation of a rate-sensitive tolerable compression led to the introduction of the Viscous criterion, VC max , which accounts for the importance of both parameters. VC max is the maximum of the product of velocity of deformation ( V) and compression ( C), and is derivable from the chest deflection response. This paper presents the empirical evidence and theoretical basis supporting the Viscous criterion, and shows it to be an indicator of the energy dissipated by soft tissue deformation. The Viscous criterion accurately predicts the risk of vital organ and soft tissue injury when other criteria fail.

The viscous criterion—A new index of injury induced by high speed impact

The viscous criterion—A new index of injury induced by high speed impact

Viscous fracture criterion in the plastic molding of metals

Viscous fracture criterion in the plastic molding of metals