Oblique Loading Research Articles

Model Test of the Pullout Bearing Capacity of End-Bearing Torpedo Anchors

Torpedo anchors (TAs) are regarded as one of the most efficient mooring solutions for taut mooring systems, and end-bearing TAs are a new type of TA that primarily relies on end-bearing plates at the tail to generate a pile-end resistance to improve their pulloutbearing capacity (P). Therefore, the estimation of the pullout capacity of the end-bearing TA is vital for the design of offshore floating facilities. In this study, pullout model tests were conducted to investigate the P of conventional and end-bearing TAs and examine the effects of factors such as the embedment depth (h), the relative density (Dr), the pullout angle (α), and the area (A) of the bearing plates on P. The test results show that, under oblique pullout loading, the P on the conventional TA increased slowly as displacement increased, while there was a peak on the load–displacement curve of each end-bearing TA with a relatively large A. The end-bearing TAs considerably outperformed the conventional TAs in terms of the P. In addition, increasing h, Dr, and A significantly increased the P of the end-bearing TAs. However, increasing h and Dr slightly decreased the ability of the bearing plates to increase the P of the end-bearing TAs. These research results can provide a guideline for TA installation in deep-sea engineering.

Biomechanical Analysis of Different Framework Design, Framework Material and Bone Density in the Edentulous Mandible With Fixed Implant-Supported Prostheses: A Three-Dimensional Finite Element Study.

The objective of this finite element study was to investigate the effect of different framework designs, framework materials, and bone densities on the stress distribution of fixed implant-supported prostheses for edentulous mandibles. Under the condition of 2-mm cortical bone, 16 models were created in the edentulous mandible to simulate different framework designs (1-piece or 3-piece frameworks) with different framework material (pure titanium, zirconia, polyetheretherketone, or carbon fiber-reinforced polyetheretherketone) in-high or low-density trabecular bone. Then, vertical loading and oblique loading at 75° were applied to the anterior and posterior regions. The stress distribution and stress concentration region of implant and peri-implant bone with different combinations were compared by finite element analysis. The use of the 1-piece zirconia framework in high-density trabecular bone improved stress distribution on implants and peri-implant bone. The region of stress concentration is located in thebuccal cervix of the distal implants and the distobuccal portion of the cortical bone in all models. To improve the stress distribution on fixed implant-supported dentures for edentulous mandibles, the 1-piece framework and zirconia represent the better combination. Under the condition of 2-mm cortical bone thickness, the full-arch zirconia framework had minimum von Mises stress on implants and peri-implant bone in all models, and high trabecular bone density greatly decreased the stress on cortical bone.

Biomechanical comparison of different prosthetic materials and posterior implant angles in all-on-4 treatment concept by three-dimensional finite element analysis.

The study aimed to evaluate the biomechanical behaviors of different prosthetic materials and posterior implant angles in All-on-4 implant-supported fixed maxillary prostheses with three-dimensional (3D) finite element analysis. The model of complete edentulous maxilla was created using the Rhinoceros and VRMesh Studio programs. Anterior vertical and 17°- and 30°-angled posterior implants were positioned with All-on-4 design. Straigth and angled multi-unit abutments scanned using a 3D scanner. Two different prosthetic superstructures (monolithic zirconia framework and lithium disilicate veneer (ZL) and monolithic zirconia-reinforced lithium silicate (ZLS)) were modeled. Four models designed according to the prosthetic structure and posterior implant angles. Posterior vertical bilateral loading and frontal oblique loading was performed. The principal stresses (bone tissues-Pmax and Pmin) and von Mises equivalent stresses (implant and prosthetic structures) were analyzed. In all models, the highest Pmax stress values were calculated under posterior bilateral loading in cortical bone. The highest von Mises stress levels occured in the posterior implants under posterior bilateral load (260.33 and 219.50MPa) in the ZL-17 and ZL-30 models, respectively. Under both loads, higher stress levels in prosthetic structures were shown in the ZLS models compared with ZL models. There was no difference between posterior implant angles on stress distribution occurred in implant material and alveolar bone tissue. ZLS and ZL prosthetic structures can be reliably used in maxillary All-on-4 rehabilitation.

Crashworthiness analysis of multilayered hexagonal tubes under axial and oblique loads

Thin-walled structures are inevitably subjected to oblique loads which could result in poor crashworthiness. To improve comprehensive crashworthiness, multilayered hexagonal tubes with 2 to 9 layers denoted as L2 to L9 were proposed, and their crash performances were investigated under axial and oblique quasi-static loads. Based on four crashworthiness criteria, complex proportional assessment (COPRAS) and TOPSIS methods were adopted to select out two optimal structures, L2 and L3. Further multiobjective optimizations of L2 were conducted. When selecting the best configuration using the COPRAS method, structures with lower peak crushing force (PCF), higher PCF, specific energy absorption (SEA) and crushing force efficiency (CFE) are preferred. The results are opposite using the TOPSIS method.

Crash behavior and optimization of double tubes with different cross section

Finite element analysis of double tubes under axial and oblique loads are presented in this paper. This study tested double tubes which consisted of an outer tube and an inner tube. The inner tube used varied, in terms of shape, including the form of a triangle, square, hexagon, and octagonal. The crash behavior of the four types of tubes are first investigated by nonlinear finite element analysis through ABAQUS. It is found that the octagonal tube has the best crashworthiness performance under axial impact regarding both specific energy absorption (SEA) and peak crushing force (PCF). Then, the variations in the loading angle were analyzed in the oblique test category for octagonal tubes with angular variations of 10°, 20°, and 30°. In addition, optimization design of the octagonal tube is performed by adopting multiobjective nueral network algorithm to achieve maximum SEA capacity and minimum TEA with and without considering load angle effect. It is found that the optimal designs of the octagonal tubes under different load angles.

Energy absorption analysis on variable thickness CFRP/aluminum hybrid square tubes under oblique loading

The variable thickness hybrid square (VTHS) tubes are used to improve the energy absorption under oblique loading and the relative advantages compared with the uniform thickness hybrid square (UTHS) tubes are studied. First, a oblique compression test and finite element model were established to analyze the deformation mode and load-displacement curve of VTHS tube. Then, the parameter studies of VTHS and UTHS tubes were carried out. The results show that increasing thickness leads the structures to be prone to global bending mode, and the energy absorption performance is reduced. Compared with UTHS, VTHS tubes can increase the specific energy absorption when the progressive crushing mode occurred at the same loading angle. Meanwhile, the progressive crushing deformation with excellent energy absorption performance can still appear when the loading angle exceeds 30°. Finally, a unified equation for the relationship between the dimensionless mean crushing force and the loading angle was proposed.

On novel foam-filled double-hexagonal tube for multiple load cases

In this article, novel foam-filled double-hexagonal tubes (F-DHTs) are proposed and investigated for multiple load cases. First, the finite element (FE) models of DHTs with four different foam filler modes under axial and multiangle oblique impact loading are built and verified by experiment. The four foam filler modes are, respectively, Hollow-Hollow-DHT, Filled-Hollow-DHT, Hollow-Filled-DHT and Filled-Filled-DHT (FF-DHT). Second, a comprehensive crashworthiness comparison is conducted among the above DHTs, which discloses the relative advantage of novel F-DHTs. On this basis, taking the FF-DHT as research object, a systematic parameter influence study is implemented. Subsequently, the FF-DHT is multiobjective crashworthiness optimized by using a hybrid method. According to the optimization result, the FF-DHT obtains 16.69% higher overall specific energy absorption () yet 1.11% higher initial peak crushing force compared with the baseline design. Hence, the novel F-DHTs could be superior potential thin-walled energy-absorbers.

Comparison of Extramaxillary Anchored Implants, Tilted Implants, or Sinus Elevation Concepts on Stress Distribution in Atrophic Maxilla: A Finite Element Analysis.

To determine the von Mises stress values of extramaxillary implants anchored in zygomatic bone, known as zygomatic implants, abutments, superstructures, and principal stress values of bone under occlusal forces and to compare them with tilted implants and sinus elevation concepts. The hypothesis of the study was that there would be higher stress on zygomatic implants under occlusal forces compared with tilted implants and the sinus elevation technique due to the more angled placement of the zygomatic implants. Finite element analysis (FEA) was used to apply a force of 600 N (75 N premolars and 150 N first molar) vertically and at an angle of 20 degrees to the hybrid prosthesis with three different concepts-zygomatic implants, tilted implants, and sinus elevation-in D2 bones in six separate models. The posterior implants were tilted in zygomatic implant models (45 degrees) and tilted implant models (30 degrees). The von Mises and principal stress values formed in the models were compared by FEA. These values were also compared with the physiologic stress limit of the bone. In the zygomatic implant models, the von Mises stress values on both anterior and posterior implants were less than other models under both loading conditions. In addition, the lowest principal stress values were seen in these models. The highest von Mises stress among all models was found to be posterior implants in tilted implant models under oblique loading. In addition, the highest principal stress values were seen at posterior implants in the sinus elevation model under oblique loading. Vertical loading was found to induce less stress than loading at a 30-degree angle. Although zygomatic implants have a more angled placement, the stress values on the bone and implants are lower.

Augmentation of crashworthiness design of circular tubular structures by engraving grooves of varying depths

The use of gradiently grooved tubes has reaped emphasis in designing of crashworthiness systems for safeguard of commuters in passenger bus collisions. Also it is very essential to improve the performances of energy absorption systems of gradiently grooved profiles. The tubular structures exhibit superior energy absorption characteristics when subjected to uni-axial loading, on contrary it is highly susceptible to global bending mode when subjected to oblique loading pattern. This work proposes a novel design to enhance the crashworthiness metrics of circular tubular structures subjected to both direct and oblique loading by the engraving of grooves in circumferential direction with varying depths. The structure with varying groove configurations has undergone quasi-static and finite element simulations. The effect of friction contact interaction between the striker and the structure and critical loading angle (θ = 0˚ to 30˚) between them on energy absorption had been explored. The outcome reveals the merits of utilizing gradiently grooved tubes with varying groove depths which may be decreased from the striker end to the stationary end over the original, uniform and gradiently grooved structures subjected to direct and oblique loading patterns. The outcome of the work facilitates designer to enhance the energy absorbing performances for different loading conditions. Lastly, the designed tubular structure as crash buffer befitted in commercial automotive bus application is considered and demonstrated successfully.

Crashworthiness design of gradient bionic Al/CFRP hybrid tubes under multiple loading conditions

A “rigid and flexible” fiber-wrapped metal bionic hybrid structure (BH) is proposed, in which the fiber-reinforced composite is wrapped to make up for the “rigidity” of the material, and the gradient design plays the “flexibility” of the structure. Firstly, the CFRP enhanced stiffness is used as an induced mechanism to achieve variable stiffness design, which can avoid the complex processing problems faced by conventional design and effectively reduce the mass of the structure. Secondly, the crashworthiness of the Bionic Hybrid Thin-walled (BH) tube under axial and oblique loading angles was systematically investigated by changing the thickness parameter of the inner core Al to the outer CFRP winding angle using the validated finite element model. Finally, the prediction accuracy of three proxy models (RSM, KRG, SVR) is compared, and two optimization algorithms (NSGA-II and MOPSO) are combined to achieve the optimal crashworthiness under multi-angle loading conditions. The optimized BH tube has obvious advantages, most notably, the SEA is improved by 47.46%, 42.72% and 53.73% under axial collapse load compared with pure Al tube, pure CFRP tube and original BH tube, respectively. The results reported in this article provide valuable guidance on the design of new variable stiffness tubes.

Comparison of stress distribution between zirconia/alloy endocrown and CAD/CAM multi-piece zirconia post-crown: three-dimensional finite element analysis.

This study aimed to evaluate a digital multi-piece zirconia post-crown to restore a mandibular second molar with extensive coronal loss and limited restoration space, and to compare the stress distribution between endocrowns made of zirconia or alloy and CAD/CAM multi-piece zirconia post-crowns. Four three-dimensional finite element analysis models of a mandibular second molar with extensive coronal loss and limited restoration space were created as follows: (A) intact molar; (B) zirconia endocrown restored molar; (C) multi-piece post-crown restored-molar with tapered nail; (D) multi-piece post-crown restored molar with T-shaped nail. Models C and D were divided into two subgroups according to the material type: C1/D1, zirconia; C2/D2, NiCr alloy. The maximum modified von Mises failure criterion (mvM) stresses were calculated, and the stress distribution was recorded to analyze the effects of the restoration and material types on the biomechanical properties of dentin and prosthesis. The maximum mvM stress of dentin in model B (33.80MPa) was lower compared with models C (C1, 37.81MPa; C2, 36.36MPa) and D (D1, 36.34MPa; D2, 34.97MPa) under vertical load, but the opposite was observed under oblique load. The highest mvM stress was concentrated in the nail region located in the root canal, and the T-shaped nail values were greater than the tapered nail, whereas model D with T-shaped nail showed a lower mvM stress level in dentin compared with Model C with tapered nail. The digital multi-piece zirconia post-crown is a potential approach to restore mandibular second molars with extensive coronal loss and limited restoration space. The digital multi-piece zirconia post-crown has potential to restore mandibular second molars with extensive coronal loss and limited restoration space using an innovative approach.

Design of non-metallic crown for primary molars and analyzation of stress distribution: a finite element study

Objectives: To study the design of nonmetallic crowns for deciduous molars by means of computer aided design and to analyze the key parameters of the nonmetallic crowns of deciduous molars using finite element method. Methods: The three-dimensional model of a mandibular second primary molar was constructed by using a micro-CT system. The thickness of the crown was limited to 0.5 mm and four different crown shapes (chamfer+anatomic, chamfer+non-anatomic, knife edge+anatomic and knife edge+non-anatomic) were designed. Then, the crown shape was limited as chamfer+non-anatomic and five different thicknesses of the crown (0.50, 0.75, 1.00, 1.25, 1.50 mm) were designed, and three different materials, including polyetherketoneketone (PEKK), polymethylmethacrylate (PMMA) resin and resin-infiltrated ceramic, were applied to make the crown. Stress distribution and fatigue of each component of the model under vertical and oblique loadings were analyzed by using finite element method. Non-axial retention analysis was performed on chamfer+non-anatomic crowns, made of PMMA resin, with thicknesses of 0.50, 0.75, 1.00, 1.25 and 1.50 mm. Results: Among the four crown shape designs, the chamfer+non-anatomic type crown showed the lowest von Mises stress and the highest safety factor. By comparing three different materials, the resin-infiltrated ceramic group showed obvious stress concentration on the buccal edge of the crown and the PEKK group showed stress concentration in the adhesive layer. Results of non-axial retention analysis showed that the torques required by the crowns with five thicknesses at the same rotation angle were as follows: 4 856.1, 4 038.1, 3 497.3, 3 256.3 and 3 074.3 N⋅m, respectively. The comparison of areas of the adhesives fracture among groups were as follows: 0.5 mm group < 0.75 mm group < 1.00 mm group < 1.25 mm group < 1.50 mm group. Conclusions: In the design of nonmetallic crowns for primary molars, the edge of the crown should be designed as chamfer, the shape of the inner crown should be non-anatomical and the minimum preparation amount of the occlusal surface should be 1.00 mm. Among the three materials, PMMA resin, of which elastic modulus is similar to the dentin and the dental adhesive, might be the most suitable material for the crowns of primary molars.

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.

Interactive Effects of Five Dental Implant Design Parameters on the Peak Strains at the Interfacial Bone: A Finite Element Study.

The aim of this study was to evaluate and compare the effect of changing five macrostructural design parameters of dental implants on the peak strains experienced by the interfacial bone. Five geometric variables, including three body-related (implant length, diameter, and taper) and two thread-related (thread depth and thread angle) parameters, were defined. The alveolar bone was modeled as a block with anisotropic and linearly elastic properties with 20-mm height and 12-mm buccolingual and mesiodistal dimensions. Oblique occlusal loads (100-N vertical and 20-N horizontal) were applied to the abutment surface. A total of 162 models with different designs were defined by implementation of a full-factorial design. The peak values of the compressive and tensile principal strains in the cortical and cancellous bones were calculated by finite element analysis (FEA). Implant diameter and length had maximum and minimum effects on the peak compressive and tensile strains at the cortical interface, respectively. Implant diameter and thread depth had maximum and minimum effects on the maximum compressive strain at the cancellous interface, while thread angle and length had maximum and minimum significant effects on the maximum tensile strain at the cancellous interface. The interaction of thread parameters and taper has the greatest effect on the peak compressive and tensile strains at the cancellous interface and also on the peak tensile strain at the cortical interface, while body-related parameters are more effective on the peak compressive strain at the cortical interface.

Fatigue Resistance of 3-Unit CAD-CAM Ceramic Fixed Partial Dentures: An FEA Study.

To estimate the fatigue life of 3-unit molar fixed partial dentures (FPDs) made from two different monolithic ceramic systems, zirconia cercon (ZC) and lithium disilicate (LD). The effect of the connector size on the fatigue resistance of the monolithic FPD was also investigated. Two models for the FPDs were built, a 3-unit all-ceramic and a porcelain-fused-to-metal. The porcelain-fused-to-metal FPD model was used as the control. Actual 3-unit FPDs (replacing the second lower premolar) were constructed using a computer aided design and computer-aided manufacturing (CAD-CAM) system. Finite element analysis (FEA) was executed. A hemispherical indenter was used to simulate occlusal load. The occlusal load phase of the chewing cycle was applied at the premolar pontic. The failure location for the monolithic FPD was always located at the distal connector. Connector size played a key role in determining the long-term survival of the prosthesis. The fatigue resistance was predicted to be 670 N for the ZC with a connector size 4 × 3 mm, while it was only 226 N for LD. As for porcelain-fused-to-metal (PFM), FEA predicts that fatigue resistance can reach up to 770 N. Under the cyclic load of 670 N, the fatigue life for the zirconia FPD with connector size 4 × 3 mm was 2.23 × 106 cycles while it survived only 3.1 × 105 cycles when the connector was reduced to 3.5 × 2.5 mm. The angle of the oblique load has a significant effect on the stress distribution. 3-unit monolithic FPDs made of ZC have superior fatigue performance compared to those made of LD. The fatigue life of the zirconia FPD was about three times longer than that made of LD with a connector size of 4 mm × 3 mm. The survival rates of ZC FPDs are comparable to porcelain-fused-to-metal. A significant reduction in fatigue strength is predicted for reduced connector size. Therefore, it is necessary to establish general guidelines for the minimum connector size.

Biomechanical finite element analysis of short-implant-supported, 3-unit, fixed CAD/CAM prostheses in the posterior mandible

ObjectiveTo assess the biomechanical effects of different prosthetic/implant configurations and load directions on 3-unit fixed prostheses supported by short dental implants in the posterior mandible using validated 3-D finite element (FE) models.MethodsModels represented an atrophic mandible, missing the 2nd premolar, 1st and 2nd molars, and rehabilitated with either two short implants (implant length-IL = 8 mm and 4 mm) supporting a 3-unit dental bridge or three short implants (IL = 8 mm, 6 mm and 4 mm) supporting zirconia prosthesis in splinted or single crowns design. Load simulations were performed in ABAQUS (Dassault Systèmes, France) under axial and oblique (30°) force of 100 N to assess the global stiffness and forces within the implant prosthesis. Local stresses within implant/prosthesis system and strain energy density (SED) within surrounding bone were determined and compared between configurations.ResultsThe global stiffness was around 1.5 times higher in splinted configurations vs. single crowns, whereby off-axis loading lead to a decrease of 39%. Splinted prostheses exhibited a better stress distribution than single crowns. Local stresses were larger and distributed over a larger area under oblique loads compared to axial load direction. The forces on each implant in the 2-implant-splinted configurations increased by 25% compared to splinted crowns on 3 implants. Loading of un-splinted configurations resulted in increased local SED magnitude.ConclusionSplinting of adjacent short implants in posterior mandible by the prosthetic restoration has a profound effect on the magnitude and distribution of the local stress peaks in peri-implant regions. Replacing each missing tooth with an implant is recommended, whenever bone supply and costs permit.

Comparison of the strain developed around implants with angled abutments with two reinforced polymeric CAD-CAM superstructure materials: An in vitro comparative study

Statement of problemThe strain developed around implants with angled abutments should be considered when selecting a superstructure material. Studies that evaluated the strain developed around implants with angled abutments when using fiber-reinforced polymer as the implant superstructure material are lacking. PurposeThe purpose of this in vitro study was to assess the strain developed around implants with angled abutments (15 and 25 degrees) of biocompatible high-performance polymer (BioHPP) and reinforced nanohybrid polymer with a multilayered glass fiber (TRINIA) superstructure under axial and oblique loading. The strain developed around implants was evaluated by using strain gauges. Material and methodsThirty-two polyurethane test blocks were divided into 2 main groups (n=16) according to the degrees of buccal tilting of the implant platform (15 and 25 degrees). Each group was divided into 2 subgroups (n=8), and each subgroup received different superstructure materials (BioHPP or TRINIA). Two buccal and palatal strain gauges were installed on their corresponding prepared sites to measure the microstrains in the medium surrounding the implant. A universal testing machine was used to apply the static load from 0 to 100 N in the axial and 45-degree oblique direction, with the loading tip of the device on the loading point at the central fossa of the crown. For each tested implant, loads were applied, microstrains were recorded with the strain gauges, and the strain developed around the implant was statistically evaluated with 1-way ANOVA, followed by multiple pairwise comparisons by using the Bonferroni adjusted significance level (α=.05). ResultsFor superstructure materials, the microstrain values recorded around implants restored with TRINIA were significantly lower than those restored with BioHPP in all groups (P<.001). The 25-degree implant angulation recorded significantly higher microstrain than 15 degrees buccally and palatally when axial and oblique loads were applied (P<.05). The microstrain was significantly higher in the oblique load than in the axial load in both the BioHPP and TRINIA groups in 15- and 25-degree implant angulations on the buccal and palatal sides (P<.001). ConclusionsThe strain developed around dental implants was significantly affected by the superstructure material. The microstrain was considerably higher when the implant abutment angulation increased. When a 45-degree loading direction was used, this tendency became more pronounced.

Assessment of in situ chest deflection of post mortem human subjects (PMHS) and personalized human body models (HBM) in nearside oblique impacts

Objective The present study has three objectives: First, to analyze the chest deflection measured in nearside oblique tests performed with three post mortem human subjects (PMHS). Second, to assess the capability of a HBM to predict the chest deflection sustained by the PMHS. Third to evaluate the influence on chest deflection prediction of subject-specific HBM. Methods Three dimensional chest deformation of five anterior chest landmarks was extracted from three PMHS (A-C) in three sled tests. The sled test configurations corresponded to a 30 degree nearside oblique impact at 35 km/h. Two different restraint system versions (RSv) were used. RSv1 was used for PMHS A and B while RSv2 was used for PMHS C. The capability of the SAFER HBM (called baseline model) to predict PMHS chest deflection was benchmarked by means of the PMHS test results. In a second step, the anthropometry, mass and pre-impact posture of the baseline HBM were modified to the PMHS-specific characteristics to develop a model to assess the influence of personalization techniques in the capability of the human body model to predict PMHS chest deflection. Results In the sled tests, the measured sternum compression relative to the eighth thoracic vertebra in the PMHS tests was 49, 54 and 55 millimeters respectively. The HBM baseline model predicted 48%, 43% and 34% of the deflections measured in the PMHS tests, while the personalized version predicted 38%, 34% and 28%. When chest deflection was analyzed in x-, y- and z-direction for the five chest landmarks it was found that neither the baseline HBM nor the personalized model predicted x, y and z axis deflections. Conclusions The PMHS in situ chest deflection was found to be sensitive to the variation in restraint system and the three PMHS exhibited greater values of lower right chest deflection compared to what was found in available literature. The baseline HBM underpredicted peak chest deflection obtained in the PMHS test. The personalized model was not capable of predicting the chest deflection sustained by the PMHS. Hence, further biofidelity investigations have to be carried out on the human body thorax model for oblique loading.

Crashworthiness analysis of shrink circular tube energy absorbers with anti-climbers under multiple loading cases

Energy-absorbing structures with anti-climbers for railway vehicles rarely experience pure axial loading in real crash events, but rather a combination of axial and off-axial loads. In this perspective, it is critical to understand the non-centric collision process of energy absorbers. To address this issue, this paper aims to investigate the crashworthiness of shrink circular tube energy absorbers with anti-climbers under vertical, horizontal eccentric and oblique loads comprehensively. Finite element (FE) models of the shrink circular tube energy absorber with anti-climbers are then developed and validated by a physical impact experiment. The numerical results show that the different eccentric distances and oblique angles affect the crashworthiness of the proposed energy absorber significantly. The energy-absorbing structure exhibits a stable and controlled deformation pattern as well as a very high energy absorption efficiency in offset collisions at different vertical heights. However, when the horizontal offset distance exceeds half of the anti-climber width, the energy-absorbing circular tube suffers an overall destabilizing deformation, failing in the energy-absorbing capacity. Additionally, the proposed energy absorber is suitable for oblique load collision scenarios that the oblique angle is no more than 10°. Finally, the response surface modeling technique and non-dominated sorting genetic algorithm are employed to optimize the key structural parameters of shrink circular tube energy absorbers under multiple loading cases. The results exhibit that an optimized shrink circular tube energy absorber is more competent in crashworthiness for multiple load cases.

Biomechanical influence of thread form on stress distribution over short implants (≤6mm) using finite element analysis.

The macro and micro design is essential to the biomechanical performance of a short implant. In this study, the implant thread parameters of short implants used in edentulous maxillae will be discussed. The aim of the study is to analyse biomechanical distinctions in different thread parameters over short implants by applying the vertical or oblique load of 130N on dental prosthesis. A 6*5mm implant will be used in posterior maxillae arch, where the molar region locates. The CAD model has been assembled by three parts, a crown, an implant system and a jaw. By applying the vertical or oblique load to the crown, the Von-Mises stresses of cortical bone and trabecular bone will be evaluated in pairs along the lines v1-v2 & a1-a2. The results showed that the reverse buttress thread would induce more stresses in cancellous bone whereas the buttress did the opposite. The trapezoidal thread (V-thread) is more favourable than thereverse buttress thread in accordance to the FEA result. The rectangle threads will induce more uneven stresses in cancellous bones.