RETRACTED ARTICLE: Human vulnerability assessment based on bullet motion and cavity expansion model with tissue identification.

We, the authors, Editors and Publisher of the journal Computer Methods in Biomechanics and Biomedical Engineering, have retracted the following article:Jia, Y., Wen, Y., Dong, F., Qin, B., & Liu, R. (2024). Human vulnerability assessment based on bullet motion and cavity expansion model with tissue identification. Computer Methods in Biomechanics and Biomedical Engineering, 1-15. https://doi.org/10.1080/10255842.2023.2294263Since publication, the authors noticed an error in the setting of the model parameters during post-publication review of the methods and results.As this directly impacts the validity of the reported results and conclusions, the authors alerted the issue to the Editor and Publisher. All have agreed to retract the article to ensure the integrity of the scholarly record.We have been informed in our decision-making by our editorial policies and the COPE guidelines.The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as 'Retracted'.

Impact Response Features and Penetration Mechanism of UHMWPE Subjected to Handgun Bullet.

Ensuring military and police personnel protection is vital for urban security. However, the impact response mechanism of the UHMWPE laminate used in ballistic helmets and vests remains unclear, making it hard to effectively protect the head, chest, and abdomen. This study utilized 3D-DIC technology to analyze UHMWPE laminate's response to 9 mm lead-core pistol bullets traveling at 334.93 m/s. Damage mode and response characteristics were revealed, and an effective numerical calculation method was established that could reveal the energy conversion process. The bullet penetrated by 1.03 mm, causing noticeable fiber traction, resulting in cross-shaped failure due to fiber compression and aggregation. Bulge transitioned from circular to square, initially increasing rapidly, then slowing. Maximum in-plane shear strain occurred at ±45°, with values of 0.0904 and -0.0928. Model accuracy was confirmed by comparing strain distributions. The investigation focused on bullet-laminate interaction and energy conversion. Bullet's kinetic energy is converted into laminate's kinetic and internal energy, with the majority of erosion energy occurring in the first four equivalent sublaminates and the primary energy change in the system occurring at 75 µs in the fourth equivalent sublayer. The results show the damage mode and energy conversion of the laminate, providing theoretical support for understanding the impact response mechanism and improving the efficiency of protective energy absorption.

The fatal effect of shock waves on the head of a person wearing a polyurea-reinforced ballistic helmet.

Ballistic helmets are an important part of personal protective equipment in war and are specifically designed to protect a person's head. The future trend is to improve the protective performance of helmets through the use of lightweight coatings, and polyurea, as one of the hottest elastomeric polymer coating materials in recent years, has excellent physical properties, especially its ability to improve the target's protection against blast shock waves. Therefore, in this study, using a validated head model, a blast impact model under the fluid-solid coupling method was constructed to study the effect of blast wave on the model and to analyse its effect on intracranial pressure and skull deformation. In addition, the effect of the position of the polyurea lightweight protective coating on the bending deformation of the skull under the effect of the blast wave was also investigated. The results showed that the polyurea coating could reduce the skull deformation under the same surface density condition. However, spraying polyurea on the blast surface of the helmet's blast-facing surface does not effectively reduce skull deformation caused by blast waves.

Wall thickness analysis method for judging the degree of lower extremity long bone healing.

To evaluate the possibility of judging the degree of bone healing by wall thickness analysis provide reference for quantitative analysis of bone healing. Patients with lower limb fracture from April 2014 to October 2019 were recruited and divided into bone healing (group A), poor bone healing (group B), and nonunion (group C). Models were built in Mimics 20.0 with DICOM 3.0 data obtained from patient's CT. Three-dimensional geometric models of unaffected limb and affected limb after simulated removal of internal fixation were established, corresponding to basic phase and simulated phase, respectively. Wall thickness analysis was performed to obtain median wall thickness after meshing. R2 (median wall thickness ratio), R4 (CT value ratio), and R5 (healing index ratio) were obtained by calculating the ratio of each value in simulated phase to that in basic phase. Receiver operating characteristic curve analysis was used to evaluate the ability of Wall Thickness Analysis to indicate fracture healing. 112 CT scans of 79 patients were included in the study. The frequency of categorization in groups A, B, and C was 49, 37 and 26, respectively. The median R2 in groups A, B, and C was 0.91, 0.80, and 0.67, respectively (group A > group B > group C, all P < 0.05). The best cutoff point for R2 in predicting bone healing was 0.84, and predicting bone nonunion was 0.74. The Wall Thickness Analysis can be used to quantitatively evaluate fracture healing state, with median wall thickness ratio as a more intuitive and reliable judgment index.

Experimental investigation on the characteristics of temporary cavity in BABT with 9 mm projectiles.

Temporary cavity, one physical phenomenon in BABT reflects the dynamic response of biological tissues and is used to evaluate the trauma. To clarify the characteristics of cavity evolution during 9 mm Luger penetration, we obtain the deformation profiles by using an experimental method with a high-speed camera and thereby visualize the cavity formation and development. According to the dynamic impact experiments at the velocity from 220 to 420 m/s, the temporary cavity profile can be approximately regarded as a semi-ellipsoid. The maximum depth increases as a quadratic function of velocity. Additionally, the maximum volume of the temporary cavity is attained significantly after the maximum depth. The change rate of cavity volume in the expansion stage is larger than that in the contraction stage.

Mechanical response of porcine hind leg muscles under dynamic tensile loading.

A modified split Hopkinson tension bar (SHTB) apparatus was used to investigate the dynamic tensile mechanical response of porcine muscles. A hollow aluminum alloy transmission bar and a semiconductor strain gauge were used to enhance the weak signal from porcine muscles. A ring-shaped copper pulse shaper was used to achieve stress equilibrium and constant approximate strain rates in the specimens. The thin muscle specimen, fixed by 3D-printed clamps, was warped around the bar ends to minimize the radial inertial effect during tensile loading. The quasi-static tests at strain rates of 0.1 s∧-1 were also conducted on a universal material testing machine to investigate the strain rate dependence. The true stress-strain curves of porcine muscle tissues along the fiber direction were determined at approximate strain rates of 800 s∧-1, 2000 s∧-1, and 3000 s∧-1. The experimental results show that the porcine muscle exhibits nonlinear, rate-sensitive, and orthotropic behavior. The Mooney-Rivlin model with two material constants was sufficient to represent the tensile response of porcine muscles at each strain rate. The rate-dependent Fields-Backofen model can describe the high strain rate response of the porcine muscles.

Study on nonlinear constitutive model of skin under compression load over a wide range of strain rates.

PURPOSE: In wound ballistics, skin has obvious blocking effect in the biological target penetration of projectiles. An analytical description of skin mechanical properties under compression can set the basis for the numerical simulation and the evaluation of blocking effect. METHODS: In this study, an improved three-parameter solid visco-elastic model was proposed to describe the skin creep phenomenon. And then combined with Maxwell and Ogden model, a new nonlinear skin constitutive model, consisting of hyper-elastic unit, creep unit and relaxation unit in parallel, was established. Here, we examine the material properties of freshly harvested porcine skin in compression at strain rates from 0.01/s to 4000/s. RESULTS: The model is verified by comparison with the experimental results by our test and that in the literature at different strain rates. CONCLUSIONS: It shows that calculated results of the constitutive model agree well with the experiment data at extremely low to high strain rates, which is useful for the description of the heterogeneous, nonlinear viscoelastic, relaxation and creep mechanical response of skin under compression.

Transient pressure wave in the behind armor blunt trauma: experimental and computational investigation.

In the last few decades, various researches focus on the transient pressure in the behind armor blunt trauma. This paper presented a investigation on the transient pressure in the ballistic gelatin behind a soft body armor subjected to the impacting from three ammunitions. Experimental results show that three peaks appear on the pressure-time curves without taking into account the ammunition type and the impact velocity. Furthermore, numerical models of the test were created to compare modelling results to the pressure from the pressure gauges buried in the gelatin block. The main features on the pressure-time cure were discussed to analyze the wave formation and propagation. With the verified model, the effect of the boundary was also investigated to explain the wave reflection which appeared after two peaks.

Rifle bullet penetration into ballistic gelatin.

The penetration of a rifle bullet into a block of ballistic gelatin is experimentally and computationally studied for enhancing our understanding of the damage caused to human soft tissues. The gelatin is modeled as an isotropic and homogeneous elastic-plastic linearly strain-hardening material that obeys a polynomial equation of state. Effects of numerical uncertainties on penetration characteristics are found by repeating simulations with minute variations in the impact speed and the angle of attack. The temporary cavity formed in the gelatin and seen in pictures taken by two high speed cameras is found to compare well with the computed one. The computed time histories of the hydrostatic pressure at points situated 60 mm above the line of impact are found to have "two peaks", one due to the bullet impact and the other due to the bullet tumbling. Contours of the von Mises stress and of the effective plastic strain in the gelatin block imply that a very small region adjacent to the cavity surface is plastically deformed. The angle of attack is found to noticeably affect the penetration depth at the instant of the bullet tumbling through 90°.

The experimental and numerical study of indirect effect of a rifle bullet on the bone.

We study the transient indirect effect of a rifle bullet on bone in the gelatin-bone composite target experimentally and computationally. The process of a 56 type 7.62-mm rifle bullet penetrating the composite target has been simulated using numerical method. The experiment provided the criteria for verifying the correctness of the numerical model. We have obtained tomographic data of bone by CT scans, and also defined the bone as different layers by the gray scale to simulate its heterogeneity. The computed results are in good agreement with the experimental data. Effects of the impact velocity and bone location on damage caused to the composite target have also been studied. The numerical results imply the follows: When the velocity of bullet increases, the stress on bone also increases with the earlier pressure peak; When the bone is located in a certain distance from the trajectory, it will not be fractured, although it is affected by the stress wave.

Analysis of behind the armor ballistic trauma.

The impact response of body armor composed of a ceramic plate with an ultrahigh molecular weight polyethylene (UHMWPE) fiber-reinforced composite and layers of UHMWPE fibers shielding a block of ballistic gelatin has been experimentally and numerically analyzed. It is a surrogate model for studying injuries to human torso caused by a bullet striking body protection armor placed on a person. Photographs taken with a high speed camera are used to determine deformations of the armor and the gelatin. The maximum depth of the temporary cavity formed in the ballistic gelatin and the peak pressure 40mm behind the center of the gelatin front face contacting the armor are found to be, respectively, ~34mm and ~15MPa. The Johnson-Holmquist material model has been used to simulate deformations and failure of the ceramic. The UHMWPE fiber-reinforced composite and the UHMWPE fiber layers are modeled as linear elastic orthotropic materials. The gelatin is modeled as a strain-rate dependent hyperelastic material. Values of material parameters are taken from the open literature. The computed evolution of the temporary cavity formed in the gelatin is found to qualitatively agree with that seen in experiments. Furthermore, the computed time histories of the average pressure at four points in the gelatin agree with the corresponding experimentally measured ones. The maximum pressure at a point and the depth of the temporary cavity formed in the gelatin can be taken as measures of the severity of the bodily injury caused by the impact; e.g. see the United States National Institute of Justice standard 0101.06-Ballistic Resistance of Body Armor.

Nattokinase decreases plasma levels of fibrinogen, factor VII, and factor VIII in human subjects.

Nattokinase, a serine proteinase from Bacillus subtilis, is considered to be one of the most active functional ingredients found in natto. In this study, we hypothesized that nattokinase could reduce certain factors of blood clotting and lipids that are associated with an increase risk for cardiovascular disease (CVD). Thus, an open-label, self-controlled clinical trial was conducted on subjects of the following groups: healthy volunteers (Healthy Group), patients with cardiovascular risk factors (Cardiovascular Group), and patients undergoing dialysis (Dialysis Group). All subjects ingested 2 capsules of nattokinase (2000 fibrinolysis units per capsule) daily orally for 2 months. The laboratory measurements were performed on the screening visit and, subsequently, regularly after the initiation of the study. The intent-to-treat analysis was performed on all 45 enrolled subjects. By use of mixed model analysis, a significant time effect, but not group effect, was observed in the change from baseline of fibrinogen (P = .003), factor VII (P < .001), and factor VIII (P < .001), suggesting that the plasma levels of the 3 coagulation factors continuously declined during intake; also, the extents of decrease were similar between groups. After 2 months of administration, fibrinogen, factor VII, and factor VIII decreased 9%, 14%, and 17%, respectively, for the Healthy Group; 7%, 13%, and 19%, respectively, for the Cardiovascular Group; and 10%, 7%, and 19%, respectively, for the Dialysis Group, whereas blood lipids were unaffected by nattokinase. No significant changes of uric acid or notable adverse events were observed in any of the subjects. In summary, this study showed that oral administration of nattokinase could be considered as a CVD nutraceutical by decreasing plasma levels of fibrinogen, factor VII, and factor VIII.