Higher Stress Values Research Articles

Design and Structural Analysis of Trailer Sliding Underrun Protection Device Complied with ECE R58.03 Regulation

In this study, a new, innovative design and structural analysis of trailer sliding rear underrun protection device (RUPD) that complied with UN ECE R58.03 regulation has been made. The technical design norms that determined by United Nations (UN) were considered the key factor for the design parameters. Finite Element Analyses (FEA) were carried out considering the strength test standards specified in the UN ECE R58.03 regulation. Stress distribution was evaluated in the analyzes applied to RUPD. According to stress result of the P1 test condition analysis, the highest stress value was obtained as 839 MPa on hinge mechanism’s pins and also during the P2 condition the stress level on same pins were above 1100 MPa. Considering the stress datas from FEA, it was concluded that the design had to be revised. After revision the stress levels decreased, but levels were close to the yield strength of materials that used. Based on all data obtained, authors decided that design is trustworthy enough to be produced and physical tested, but after the physical testing additional minor revisions may be needed.

Investigation of the biomechanical stability of Cfr-PEEK in the treatment of mandibular angulus fractures by finite element analysis

The purpose of this study is to explore the effectiveness of Cfr-PEEK, in the fixation of unfavorable fractures of mandibular angulus by comparing it with the titanium and resorbable biomaterials. 8 different fixation models were created. In the first 4 groups, a single mini plate was applied to the upper edge of the fracture line by the Champy method. In the other 4 groups, an additional plate was placed on the lower edge of the fracture line. In these models, titanium, resorbable and Cfr-PEEK plate/screw systems were investigated by the finite element analysis method. The highest Von Mises stress was observed on the upper plate in the group 5 while the lowest was seen in the lower plate in the group 7. The highest stress values on the screws were observed on the screws placed closer to the fracture line. Considering the stresses on the bone around the screws, the highest Pmax and Pmin values were seen in group 5, and the lowest values were seen in the group 7. The highest displacement was observed in the group 3, while the lowest was observed in the group 5. According to the results it can be said that Cfr-PEEK plate/screw systems may provide advantages by decreasing the stresses on the fixation systems over the titanium plates and providing more stable fixation over the resorbable systems. Cfr-PEEK plates of 2 mm thickness seems to be a potential alternative to 1 mm thick titanium plates.

Effect of Quenching Parameters on Distortion Phenomena in AISI 4340 Steel

During quenching heat treatment, the formation of high residual stress values and the presence of distortion are phenomena which are difficult to control and accurately predict, their effects being extremely important to the components or pieces of complex and robust geometry that are commonly used in the industry. The latter is mainly due to the mixture of the high temperature levels formed between the surface and the cores of the components and the martensitic transformation during quenching. In this research, an experimental and simulated analysis of the process of the quenching heat treatment of AISI 4340 steel, using geometrically complex components, was undertaken with the objective of studying and understanding the effect of quenching process parameters on distortion, stress generation, and mechanical properties. A model that applied the finite elements method (FEM), in which entry data such as thermo-physical and mechanical properties were obtained through experimental techniques that were reported in the literature, made it possible to simulate the cooling process under different conditions, which helped to explain the origins of the distortion in the quenched parts. The results show a close relationship between various quenching parameters such as heat extraction speed, the immersion orientation in the liquid, and the component’s geometry. The data obtained could contribute to accelerating the design process of the heat processing routes for quenching components by taking into consideration both the classic process variables and, due to the increased precision resulting from mathematical modeling, additional factors such as the geometry of real applications.

Comprehensive Evaluation of Rock Mechanical Properties and in-situ Stress in Tight Sandstone Oil Reservoirs

Comprehensive research on reservoir rock mechanics and in-situ stress properties combined with petrophysical experiments, logging models and numerical simulation is an important means to achieve efficient development of tight sandstone oil reservoirs. In this study, a large number of rock mechanics and acoustic experiments, full-wave train array acoustic wave tests, hydraulic fracturing data and three-dimensional finite element simulations were used to study the rock mechanical properties and in-situ stress characteristics of continental tight oil reservoirs in the Yanchang Formation. The results show that under uniaxial conditions, the tight sandstone samples mainly suffer from tensional ruptures. With the increase of confining pressure, the tight sandstone samples undergo obvious shear ruptures. When the confining pressure is loaded to 35 MPa, a typical vertical shear fracture will be formed. The hydraulic fracturing calculation results show that the in-situ stress state of the target layer satisfies σv (vertical principal stress)>σH (maximum horizontal principal stress)>σh (minimum horizontal principal stress). Based on the results of rock mechanics and acoustic tests, we have constructed the dynamic and static mechanical parameter conversion models of tight oil reservoirs and the logging interpretation model of current in-situ stress. Furthermore, the finite element method is used to simulate the three-dimensional structural stress field of the target layer. The simulations show that the horizontal principal stress distribution in the work area is consistent with the applied environmental stress. The σH of the target layer is mainly distributed in 32–50 MPa, and the σh is mainly distributed in 20–34 MPa. Both σH and σh are relatively high in the southern uplift of the work area; among them, σH is usually greater than 44 MPa, and σh is usually greater than 24 MPa. The northern part of the study area developed several grooved areas with relatively low stress values. The regions with high stress values are often distributed in bands, which may be related to the compression caused by the deformation of the strata. For shear stress, left-handed and right-handed regions usually alternate with each other. However, the extent of the left-handed area in the southern uplift area is larger than that of the right-handed area, indicating that the tight oil reservoirs in the study area are mainly affected by left-handed activities.

Bone quality effect on short implants in the edentulous mandible: a finite element study

IntroductionThe aim of this study was to verify whether the use of short implants could optimize stress distribution of bone surrounding implants in atrophic mandibles with different bone qualities.MethodsA three-dimensional model of the atrophic mandible with three levels of bone quality was made using computer software. Short implants (6 mm) and standard implants (10 mm) were used in four designs: Design 1 "All-On four", Design 2 "All-On-four" with two short implants, Design 3 four vertical implants with two short implants, and Design 4 six short implants. The distal short implants were placed at the first molar position. All twelve models were imported into finite element analysis software, and 110 N oblique force was loaded on the left second premolar. Maximum principal stress values of peri-implant bone and the volumes of bone with over 3000 microstrians (overload)were analyzed.ResultStress values and volumes of overload bone increased in all four groups with the decline of bone quality. The highest stress values were found in the cortical bone surrounding the Design 1 inclined implant in two lower bone quality mandibles, and the lowest in Design 3. However, Design 1 had less overload bone tissue than all three designs with short implants.ConclusionShort implants placed posteriorly helped decrease stress values in peri-implant bone, while bone surrounding short implants had a high resorption risk in low bone quality mandible.

On the effect of irregular uterine activity during a vaginal delivery using an electro-chemo-mechanical constitutive model

During a normal vaginal delivery, the muscle cells propagate electrical signals throughout the uterine wall, resulting in uterine contractions. However, uncoordinated uterine activity may disturb the uterine contractions pattern and negatively impact fetal and maternal health. Some of the abnormalities identified by the specialists are excessively short resting intervals and tachysystole. This work aims to investigate the influence of abnormal uterine activity in terms of maximum principal stress distribution and collagen fibers stretch in the uterine tissue during vaginal delivery with (i) excessively short resting intervals without changing the contraction time, and (ii) tachysystole (contraction and reduced resting times). These patterns are compared with a normal uterine contraction pattern. To achieve our aims, a biomechanical model was developed, including finite element models of the uterus and the fetus, and an electro-chemo-mechanical constitutive model. Generally, the excessively short resting intervals exhibit higher average maximum principal stresses during the contraction and resting stages, lower average fibers stretch values in the longitudinal direction and higher stretch in the circumferential direction. On the other hand, the tachysystole exhibit generally lower stress values during the uterine contraction and higher stress values during the resting stages, higher stretch in the longitudinal direction, and lower stretch in the circumferential direction.

Effect of temperature on sedimentation stability and flow characteristics of magnetorheological fluids with damper as the performance analyser

dimentation stability and high yield stress of a magnetorheological fluid (MRFs) are essential parameters for better damping performance for any practical application. Preliminary investigations have been carried out on carbonyl iron particles to determine the morphology, particle size, crystal structure, and saturation magnetization for their feasibility of synthesizing magnetorheological fluids in-house. This study synthesizes various MRFs from various commonly used carrier oils and additives. The MRF samples were prepared for 25% volume fractions of carbonyl iron (CI) powder in either silicone oil (350cSt) or hydraulic oil (50cSt) and by using lithium and calcium-based additives or a combination of both the additives. The sedimentation stability and yield behaviour at different temperatures show a remarkable drop in sedimentation rate and yield stress for all the MR fluid samples. The characterization of the prepared MR fluids reveals that MRF-1, MRF-3, MRF-5 are more stable and have high yield stress values. MRF-1 is selected to further characterize its dynamic performance in magnetorheological damper fabricated based on geometric dimensions obtained from the response surface optimization technique. The results indicate a 164.45% and 135.48% increase in damping force at higher amplitude and higher frequencies at 0A and 1A currents. Further, similar tests have been carried out by synthesizing MRF-7 with silicone oil (50cSt) + lithium base grease as the additive. The sample's stability and yield stress with temperature are carried out, and performance analysis shows a remarkable change in damping force than MRF-1. The dynamic range obtained is practically viable in MRF-7 than MRF-1, with less variability. Finally, temperature characteristics captured from the thermocouple of the MR damper reveal that an average of 43.78% reduction in damping force when the temperature is increased by 19.5 °C with increased dynamic range.

Finite Element Analysis for Safe Design of a Flexible Microelectronic System under Bending Deformation

We modeled flexible microelectronic systems and analyzed the stress and strain distribution assuming an international standard bending test evaluating flexible electronics. The flexible microelectronic system consisted of a flexible substrate, a thin silicon die bonded to the substrate using bumps, along with an underfill and molding layer. The highest stress values were found at the square silicon die corners under bending deformation. After rounding the die corners, the copper bumps were the weakest component in the system. When polymer bumps replaced copper bumps to improve the mechanical stability, the critical bending radius reduced from 13.5 mm to 8.0 mm, and the silicon die was again the most vulnerable component. When the die thickness decreased from 50 to 30 μm, the critical bending radius of the flexible system even decreased to 6.9 mm. Therefore, it is advantageous for mechanically reliable flexible microelectronic systems to bond thin silicon dies with rounded corners to a flexible substrate using polymer bumps.

The Influence of Different Occlusal Loading on Six Restorative Materials for Restoration of Abfraction Lesions—Finite Element Analysis

The aim of the study was to analyze the occurrence of stress on teeth with abfraction lesions restored with six different restorative materials, and by introducing the tensile strength parameters to calculate the safety factor of the material under the load (ratio between the strength of the material and the maximum stress). Three-dimensional models of the mandibular premolar are created from a microcomputed tomography images. An abfraction lesion is modeled on the tooth. The stress of the dental tissues and six restorative materials under functional and nonfunctional occlusal loading of 200 (N) are analyzed by finite element method. CTAn program 1.10 and ANSYS Workbench (version 14.0) were used for analysis. Results are presented in von Mises stress. Oblique loads caused ≈ four times higher stress in restorative materials than the axial ones. It is noticeable that high values of von Mises stress are measured at the bottom of the sharp lesion, even up to 240 MPa, that are significantly reduced after the restoration. The highest stresses at the restorative material are present at the lower (gingival) margin of the restoration. The highest stresses under both types of loads are measured in nanohybrid composite (Tetric EvoCeram, Ivoclar Vivadent). The lowest values of the stress are measured in the flowable composite (Tetric Flow, Ivoclar Vivadent), but at the same time, the highest value of the stress is measured in the surrounding dental tissues on the tooth restored with the flowable composite. The microhybrid composite (Herculite XR, Kerr), with the highest safety factor, is the material that best withstands the stresses it is exposed to. The obtained safety factor did not exceed the critical limit, except for the glass ionomer cement, with the safety factor lower than 1. The type of tooth loading has the greatest influence on the intensity of stress. The value of the obtained stresses in the restorative material and dental tissues differ due to the different mechanical properties of the materials. Restoration of noncarious lesions significantly reduces extremely high stress values at their bottom.

RELATIVE DENSITY EFFECTS ON DRAINED SAND BEHAVIOR AT HIGH PRESSURES

A high-pressure triaxial compression and extension apparatus was employed to investigate the effects of initial relative density on the drained behavior of sand. Experiments were performed on cylindrical specimens of Cambria sand with initial relative densities of 30% and 60%, and compared with previously published results for 90%. Confining pressures in the range of 0.25 to 60 MPa were employed to obtain the characteristic behavior of the sand over a large range of pressures. As the confining pressure increased particle crushing increasingly influenced the stress-strain and volume change relations, producing increasing strains to failure and increasingly contractive volume changes. Beyond certain high values of mean normal stress at failure, increasing with initial relative density, the volumetric contraction and strains to failure began to decrease. The Mohr-Coulomb failure envelopes show the greatest curvature for the highest density, but the failure envelopes merge at high pressures where, due to particle crushing, the relations between void ratio and isotropic pressure are described by a single curve. The experiments show clearly that the rates of dilation at failure and the friction angles are directly related to each other, as has been proposed by many investigators. The friction angles are higher in extension than in compression for lower confining pressures, but a crossover occurs and the friction angles are higher in compression than in extension for higher confining pressures.

Biomechanical Assessment of Tilted Mandibular Second Molars with Full-Crown Adjacent to Implant-Supported Restoration: 3D Finite Element Analysis.

PurposeThe aim of this study was to investigate the effects of tooth root inclination and crown preparation angulation on the stress distribution of tilted second molars, supporting structures and adjacent implant by using the finite element analysis method.Materials and Methods3D finite element models of tilted second molar and tooth-supporting structures, including the two designs with three different angles of root inclination and crown preparation angulations, were constructed for full-crown restoration. For all models, the stress distribution was analyzed under vertical and oblique loading conditions.ResultsThe maximum equivalent stress (MES) increased as root inclination increased, and the highest stress value occurred in the tooth root furcation of the model with 30° root inclination under oblique loading. When root inclination was the same, the MES of each structure was approximate under the same direction load regardless of crown preparation angulation. Higher stress values were found on the tooth root, periodontal ligament, and cortical bone of all models under oblique load compared with vertical load. The highest stress value occurred in the distal adjacent area of implant.ConclusionTooth roots with less than 30° inclination, occlusal preparation parallel to the bite plane and small oblique force loading are recommended as significant considerations for full-crown restoration of a mesial inclined mandibular second molar.

Investigation of postero-anterior mobilization in the lumbar spine: A finite element analysis study

Background/Aim: Postero-anterior (PA) mobilization is a non-invasive treatment method traditionally used to treat low back pain (LBP) in many countries. However, the effects of PA mobilization on lumbar spine biomechanics are still unknown. The aim of this study is to determine the maximum von Mises stresses on the lumbar vertebra (L5), with force applied at different angles during PA mobilization therapy using finite element analysis (FEA). Methods: L5 vertebra CT images of a 30-year-old male patient were modeled in three dimensions (3D) with MIMICS software to examine the PA mobilization biomechanics. The resulting L5 spine model was submitted to the finite element software ANSYS (version 19) to evaluate the effects of PA mobilization. To simulate PA mobilization on the L5 vertebra, a static force of 100 N was applied over the spinal process in three different directions. The distribution of von Mises stresses occurring in the L5 spine was determined in the analyses. Results: During PA mobilization, the stress distributions on the vertebrae caused by the static force applied in three different directions in the L5 vertebra spinal process was determined. As a result of the analysis, higher stress values were found in the posterior elements of the vertebrae in all directions compared to the vertebral corpus. However, when compared according to the direction of application, the lowest stress values were detected in the pedicles and laminas in PA mobilization applied toward the spine center. Conclusion: Vertebral pedicles, laminae, and spinous process are critical areas prone to fracture. It was argued that the change in the direction of PA mobilization applied in the L5 vertebral spinal process affects the von Mises stress distributions occurring in the pedicles and laminae.

Effects of Location and Volume of Intraosseous Cement on Adjacent Level of Osteoporotic Spine Undergoing Kyphoplasty: Finite Element Analysis

Kyphoplasty (KP) is a surgery used to reduce pain and increase stability by injecting medical bone cement into broken vertebrae. The purpose of this study was to determine the ideal amount of cement and injection site by analyzing forces with the finite element method. We modeled the anatomical structure of the vertebra and injected the cement at T12. By increasing the amount of cement from 1 cc to 22 cc, stress applied to T11 and L1 cortical was calculated. In addition, stress applied to the adjacent KP level was calculated with different injection sites (medial, anterosuperior, posterosuperior, anteroinferior, and posteroinferior). After 5 cc cement was inserted, adjacent end plate stress was analyzed. In this study, break point adjacent bone stress according to the capacity of cement was bimodal. Flexion/extension and lateral bending conditions showed similar break points (11.5-11.7 cc and 18.5-18.6 cc, respectively). When cement injection was changed, front under and back under had the highest stress values among various parts, whereas the center position showed the lowest stress value. With increasing amount of bone cement, stress on the upper and lower end plates of the cemented segment increased significantly. Thus, increasing cement amount to be more than 11.5 cc has a potential risk of adjacent fracture. Centrally injected bone cement can lower the risk of adjacent fracture after percutaneous KP.

Three-dimensional comparison of the effects of sliding mechanics in labial and lingual orthodontics using the finite element method

The extraction of maxillary first premolars is usually the treatment of choice to resolve crowding, alveolar protrusion, or Class II malocclusion. The demand for a lingual orthodontic treatment is increasing because of its esthetic value; therefore, understanding lingual biomechanics is essential to every clinician. This study compared the 3-dimensional (3D) effects of sliding mechanics in labial and lingual orthodontics using the finite element method. Twelve 3D finite element models were created with different power arm heights and miniscrew positions. A 150 g of retraction force was applied from the head of the miniscrew to the power arm. The 3D displacement of the original nodes was measured, and the stress distribution on defined element zones of the periodontal ligament. Different force directions led to different movement patterns and stress distribution. The lingual models showed a more important lingual crown tipping, extrusion, and higher stress values than the labial models. Results were not affected by the vertical position of the miniscrew. Bodily en-masse retraction was not achieved in all models. Adding extra torque to the archwires is essential to prevent excessive lingual crown tipping. The lingual appliance induced more lingual tipping and extrusion of the anterior teeth. Expanding the archwire is important to minimize the risk of intercanine width reduction. The vertical position of the miniscrew does not affect the results of en-masse retraction.

Forming of properties complex of copper wire by the method of combined deformation by torsion and tension

The object of research is the mechanical properties of copper wire M1 for electrical applications, subjected to combined torsional deformation with tensile tension. One of the most problematic aspects in the manufacturing of such a wire is its fracture during processing due to low strength and ductility. DSTU EN 13602:2010 regulates the ultimate tensile strength, relative elongation, the number of bends before fracture and the number of twists until failure. To increase the service life of the product it is necessary to increase strength and plastic properties. The methods of influence on the material by combined plastic tensile deformation with tensile was used in the study, the mechanical characteristics (ultimate tensile strength, true deformation before failure, relative elongation, relative reduction in area) and electrical conductivity were determined. Statistical analysis tools were used for modeling and graphical displaying of data. The proposed approach allows to select the modes of combined torsional deformation with tensile, providing the optimal combination of tensile strength and relative narrowing of M1 grade copper wire. Under certain modes of such deformation, with increasing degree of deformation, it is possible to increase the strength characteristics and at the same time obtain high values of plasticity. The obtained results of approbation of different combined deformation modes allow to consider it an effective tool for achieving high values of true rapture stress and ultimate deformation in order to improve the service characteristics of the deformed wire. It is shown that relaxation processes occur during such treatment, which leads to a decrease in stresses and a sharp increase in plastic characteristics. Clarification of the mechanisms of the characteristics formation allows to control the features of the structure and, accordingly, the level of mechanical properties to obtain a wire that combines high strength with high toughness. This makes it possible to develop deformation modes to obtain copper wire with special properties depending on customer requirements, for example: strong wire with low electrical resistance.

Use of Smart Wearable Devices for the Acquisition and Subsequent Analysis of the Stress Level of a University Professor

This paper presents the use of a wearable device as a low-cost technological tool for estimating the stress level of a university professor. The wearable device has infrared sensors that, when in contact with the skin, allow it to know the variations in the user's heart rate and indirectly estimate stress levels through an endorsed model. An experimental methodology with a non-probabilistic convenience sample was proposed. The period of experimental evaluation was one year, 24 hours a day. A classification of the levels of stress that the university professor manages was made: relaxed, normal, medium and high. This made it possible to show the percentage of time that he held in each of these categories. Within the quantitative analysis, a differentiation was made between working days, weekends and holidays. As significant results, it was found that the working day with the highest stress values was Wednesday with a value of %59.78 and, in a non-presumptive way, Saturday was detected, despite not being a working day, the university professor reached significant levels of stress. It was possible to show that the use of low-cost wearable devices allows an estimation of the repercussions at the stress level of workloads, for which it can serve as a tool for planning and scheduling tasks.

Effect of Different Ceramic Materials on Fatigue Resistance and Stress Distribution in Upper Canines with Palatal Veneers.

The aim of this study was to evaluate, by means of a fatigue life test, different ceramic materials used in palatal veneers to restore the canine guidance. Forty-five standardized anatomical preparations were made in extracted healthy human canines with 1.2 uniform thickness. Samples were scanned, restorations were designed and milled in polymer-infiltrated ceramic network (PICN, Vita Enamic), zirconia-reinforced lithium silicate (ZLS, Vita Suprinity), and high translucent yttrium oxide-stabilized tetragonal zirconia (YZHT, Vita YZHT). Dental preparations were etched, restorations were processed according to the manufacturers' recommendations, and adhesively cemented. Then, three samples of each group were tested with load-to-fracture to determine the fatigue parameters. In addition, the palatal veneers stresses were evaluated using numerical models through finite element analysis. The mean of the monotonic test for PICN, ZLS, and YZHT was 674.18 N, 560.5 N, and 918.98 N, respectively. The StepWise test was performed until specimen fracture or until suspension of the test after 1.2 × 106 cycles. Regarding survival, using the Kaplan-Meier method, PICN presented results for the mean and median of 245.21 N and 225 N, respectively; ZLS had an average of 175.76 N and a median of 168 N, and YZHT with an average of 383.30 N and a median of 366 N. Regarding the Weibull method, PICN showed results of 5.43 β and 264 η for form and scale, respectively; ZLS had 36.14 β for form and 380.67 η for scale; and YZHT presented 4.95 β for form and 417.38 η for scale. The highest stress value was calculated for YZHT, ZLS, and PICN, respectively. It was possible to conclude that all tested materials have the possibility of being used for rehabilitation of upper canines' palatal surface.

Thermoelastic state during electrofusion welding of polyethylene pipes at different ambient temperatures

The problem of welding polyethylene pipes used in the mining industry at low ambient temperatures is considered The numerical solution of a thermoelastic problem revealed the distinctive features of thermal and stress-strain states of weld connections of polyethylene pipes using embedded heater couplings at different ambient temperatures. It is found that in low-temperature conditions, the size of the melted zone is considerably smaller than during welding at permissible temperatures. In this regard, the pressure insufficient for high-quality welding is created between the coupling and the pipe. It is also shown that at the time of melt crystallization, the maximum values of stresses and strains during welding at low temperatures are higher than during welding in the permissible temperature range, which causes high values of residual stresses. The results obtained can be used in the development of low temperature welding technology.

Study on the influence of seating orientation during frontal impacts by child occupant human body model response analysis

Objective Autonomous driving cars must be developed to ensure that children will have the highest level of protection in case of collision. Changes to the vehicle cabin design (different seat orientations, fully reclining seats, etc.) may significantly impact child occupant safety. Understanding child occupant responses under these new conditions is necessary to decrease risk and enhance child safety. In this study, child occupant response in different seating orientations exposed to frontal impacts with a focus on the head injuries and kinematics was analyzed. Methods Finite elements simulations were performed using the PIPER 6-year-old human body model (HBM). All simulations were carried out in a generic full vehicle environment. The child model was positioned in an adequate generic car restraint system (CRS) in the left rear vehicle seat in 4 seating orientations: 0° (forward-facing position), 30°, 60°, and 90° (living room position). Two scenarios were evaluated for all seating orientations according to the left front seat backrest position: reclined position nominal upright and rest position (55°). All seat configurations were subjected to the mobile progressive deformable barrier frontal impact (European New Car Assessment Programme [Euro NCAP] frontal impact testing protocol). A total of 8 scenarios were simulated in LS-DYNA. Results Based on the Euro NCAP injury risk rate, 90° seating orientation (living room position) was the safest among all selected scenarios independent of the left front seat backrest position. The worst case was found in 60° seat rotation. The highest values for Head Injury Criterion (HIC) and head acceleration (Acc 3 ms) were noted for this case. Higher Brain Injury Criterion (BrIC) values were observed at higher seat rotation angles. Hence, a 90° seating orientation showed the highest BrIC value. Attending to the skull stress, greater head injuries were caused principally by contact with the vehicle interior (seat headrest). Maximum stress values were reached at 30° and 60° seating orientations with the front seat in rest position. In 90° seating orientation, high stress values were also identified. Conclusions These results show that attending to these new seating orientations, current child safety standards are not sufficient to ensure children the highest level of protection. Other additional criteria such as BrIC or skull stress that offer a way to capture brain injuries should be used.

Impact of Portland cement type on bacterial viability in biological concrete

Biological concrete combines the advantages of traditional concrete and autonomous crack repair. As the self-healing ability of biological concrete is ensured by bacteria-induced calcium carbonate precipitation, long-term bacterial viability becomes critical. Unfortunately, the viability of bacteria tends to drop drastically within the first several days after their incorporation into biological concrete, complicating the healing process. Bacterial mortality is most often related to either the high pH values of early age concrete or mechanical stress during the mixing and hardening of the concrete. In this paper, we report a detailed analysis of the influence of cement type on bacterial viability. We reveal that a particular cement type used for concrete production is of paramount importance to bacterial viability as it directly correlates with the chemical composition of concrete and, subsequently, the environment that bacteria thrive in. We demonstrate that specific metal oxides present as impurities in cement, namely CuO and ZnO, act as bactericidal agents. To achieve the best healing effect, we suggest that the chemical composition of a given cement type is analyzed, and the inhibitory activity of each detected compound on bacteria is studied before the production of biological concrete.