Impact Location Research Articles

Impact localization of CFRP laminate based on FBG sensing and GWO-BP neural network

Carbon fiber reinforced plastic (CFRP) structures are susceptible to external energy impact during service, resulting in invisible damage. Therefore, accurate localization of these impact sites is crucial for the maintenance and safety of CFRP structures. In this paper, the strain data of the impact response of the CFRP laminate is obtained by using the fiber grating (FBG) sensor, and the data are mapped to the impact location by BP neural network. However, the traditional BP neural network is susceptible to local minima and slow convergence speed. Therefore, Grey Wolf optimization algorithm (GWO) is introduced in this study to optimize the BP neural network, which improves the convergence speed and positioning accuracy of the model. The experimental results show that the GWO-BP neural network model has excellent performance in impact positioning, with the maximum positioning error of 17.01 mm and the average positioning error of 13.05 mm. Compared with other machine learning methods, it has higher accuracy and efficiency.

Predictive modeling for hat-stiffener delamination during low velocity impact

Barely visible impact damage poses a significant threat to composite structures, particularly prevalent in the aerospace industry. The occurrence of low velocity impact (LVI) events can lead to substantial deformations in composite structures, causing interlaminar delamination and diminishing their compression load carrying capacity. Beyond LVI-induced interlaminar delamination, it is crucial to investigate failures occurring between co-cured composite structures. This study focuses on hat-stiffened coupon structures, to investigate the delaminating phenomenon between the hat and skin components. The outcomes of experimental results inform the development of a finite element model, enabling to capture the structural response and delamination dynamics. The primary objective of the experiments is to understand the delamination process which occurs suddenly upon impact. LVI experiments are conducted to understand the structural behavior at varied impact locations. A mesh study establishes the relationship between cohesive parameters and element size in the model to enable computational efficiency by avoiding the need for a highly refined mesh. When the mesh is relatively coarse, the finite element model’s capability to resolve stresses at near singular locations is limited, however the computational time is lower. Therefore, the balance between computational efficiency on the one hand, and resolving gradients on the other, requires a fine balance in order to carry out a large number of design iterations efficiently. This research significantly contributes to advancing our understanding of delamination mechanisms at free edges in composite structures, offering valuable insights for computational modeling.

Development of a method for the impact performance characterization of commonly worn helmets in rodeo bull-riding

As the rodeo sport of bull-riding increases in popularity, dangers to bull-rider athlete safety continue to pose serious health risks. Despite frequent occurrences of head trauma in the sport, current test methods for evaluating helmets commonly worn in bull-riding fail to consider rotational head acceleration, which is correlated to concussive events in impact sports. Additionally, the second most prevalent mechanism contributing to head trauma in bull-riding is bull kick impacts, which have yet to be accurately modeled in a test method. Researchers aim to enhance bull-rider athlete protection through the development of a helmet test method that simulates bull kicks with a pneumatic linear impactor. The proposed test method considers impacts at two impact velocities and six impact locations using a flat and Equestrian Hazard Anvil. Two commonly worn helmets in bull-riding are evaluated in this study, and an adequate sample size is determined from analyzing variation between repeated impacts. The proposed test method is statistically validated, and researchers show that impacts at higher kicking velocities and impacts with the flat anvil result in increased rotational head accelerations. Ultimately, this study emphasizes the need for helmets designed specifically for the unique impacts of bull-riding by simulating bull kicks through pneumatic linear impactor testing to reduce rotational head kinematics and hoof penetration.

Does pad displacement correlate to impact severity metrics in football helmets?

As efforts to reduce sport-related head injuries continue, there is a need to better understand the mechanisms of an impact that influence the risk of sustaining a concussion. This study presents a method which can be used to separate football helmet pad displacement into normal and rotational components. Finite element models of three popular football helmets were used to simulate a variety of impacts per the National Football League (NFL) helmet testing protocol. Pad displacement components were evaluated for correlation with impact severity metrics including Head Injury Criterion (HIC), Diffuse Axonal Multi-Axis General Evaluation (DAMAGE), and Head Acceleration Response Metric (HARM). When combining all locations, displacement was not found to correlate well with severity metrics ( R2 < 0.44). However, trends did exist with normal displacement when evaluating data by impact location. Normal displacement was found to correlate strongly with HARM, HIC, and Peak Resultant Linear Acceleration (PRLA) at the side upper (SU) location ( R2 = 0.79–0.8). Overall, it was observed that helmets which maximize normal displacement without bottoming out performed better. Tangential displacement was not found to correlate well with any impact severity metrics even when evaluated by location. This study has provided a method to evaluate components of helmet pad normal displacement during simulations which may help guide design and optimization efforts for helmets under impact in critical locations.

Determination of Nanoparticles and Elements in Blue Mussels (Mytilus edulis) along the Norwegian Coastline.

Our work aimed to examine nanoparticle levels in 69 distinct pooled mussel samples along the Norwegian coastline, considering samples from different environmental contexts, including natural locations, potentially polluted hotspots, and mussel farms. Single-particle ICP-MS was utilized to determine particle mass and number concentrations at environmentally relevant levels in addition to the total content of 11 elements: aluminum, barium, cerium, copper, iron, manganese, lead, silicon, silver, titanium, and zirconium. Results showed nanoparticle mass concentrations of few ng/g up to tens of μg/g and number concentrations of 106 to 109 particles/g (wet weight). Certain urban and industrially impacted locations were linked to increased levels of, e.g., silver, lead, cerium, zirconium, and titanium NPs. Farmed mussels exhibited lower concentrations. However, natural variations were considerable, and impacted locations mostly did not differ from the highest levels in pristine areas. The study presents the first extensive survey of NPs of 11 different elements in marine biota and provides evidence of increased levels of NPs in areas with anthropogenic activities.

Construction of a deterministic mathematical model for the spatial-mass distribution of random fragments produced by cased charge explosion

To evaluate the destructive effects of fragment impacts on structures or personnel, it is crucial to assess the velocity, mass, size, and impact location of the fragments, as well as establish the correlation between these factors. This paper presents the experimental measurement of fragment velocities produced by the explosion of a cased charge, the fragments resulting from the explosion are collected and steel plates are used to record the impact locations and sizes of the fragments. Based on the experimental results, the calculation models of fragment velocity, fragment mass distribution and fragment scattering angle are corrected, the spatial distribution models of fragment size and number are established, and the functional relationship between fragment mass and size is constructed. Given the aforementioned research findings, the fragment spatial-mass distribution models based on the size distribution function and based on the mass distribution function are constructed, and the fragment space-mass distributions corresponding to the number of impact regions of 1, 5 and 10 are analyzed, and the effect of the number of impact location divisions on the fragment space-mass distribution is explored. The research results show that, for the current test charge, the fragment spatial-mass distribution model based on the size distribution function aligns most accurately with experimental results when the impact regions is divided into 10. The number of impact locations designated within each region is directly proportional to the number of fragments in that specific region. Notably, the impact location of the largest fragment occurs at 0.8 times the length of the impact region, whereas the peak fragment impact density occurs at 0.743 times the length of the impact region. The spatial-mass distribution model proposed in this paper successfully correlates the velocity, mass, size and impact location of the fragments, providing a realistic theoretical representation of the spatial geometric distribution of the fragments.

Vulnerability Assessment for Naval Ships against Air-Explosive Impulses: Modified Damage-Extent Method Incorporating Structural Capacity

Abstract This study introduces an enhanced damage-extent method that incorporates the structural load-bearing capacity of the hull to assess the vulnerability of naval ships to explosive loads. This vulnerability assessment predicts the area of damage to the hull structure and calculates the probability of onboard equipment experiencing functional losses due to the explosive load, thus allowing various design alternatives to be evaluated. The proposed methodology improves upon traditional damage-volume-based approaches, such as damage-radius and ellipsoid methods, by considering the hull's structural stiffness and intrinsic damage resistance. It integrates the hull's structural resistance to the load, enhancing the damage assessment process for both the hull and equipment. This approach facilitates damage prediction for different hull designs by comparing the allowable impulse with the explosive pressure. In assessing the functionality loss and vulnerability of the equipment within the damaged hull, the network of equipment functions is considered. An anti-ship cruise missile with a sea-skimming trajectory is investigated as the explosive charge, with procedures established to simulate its trajectory and impact location on the hull. Hundreds of potential internal and external explosion points are generated, predicting the explosive pressure at each location. The shock wave, including incident overpressure, reflection pressure, and quasi-static gas pressure, is converted into impulses, taking into account the configuration of hull compartments to accurately predict these pressures and equivalent impulse. The resulting impulse is compared with the intrinsic damage capacity of each compartment's structure to assess potential damage. System network and fault tree analysis evaluate the loss of function and vulnerability of equipment within the damaged hull. Finally, the proposed capacity-based damage extent method demonstrates more accurate damage assessment compared to traditional methods, overcoming the limitations of damage-radius and ellipsoid approaches by considering hull strength

Investigation of Low Velocity Impact Behavior of Aluminum Honeycomb Sandwich Structures with GFRP Face Sheets by Finite Element Method

The aim of this study is to examine the low velocity impact behavior of aluminum honeycomb sandwich structures with glass fiber reinforced plastic (GFRP) face sheets with the help of finite element method. In the study, low velocity impact tests were carried out in the LS DYNA finite element program to examine the effects of face sheets thickness, core number, wall thickness, impact location and impact velocity on maximum contact force, absorbed energy efficiency and damage mode. Progressive damage analysis based on the Hashin damage criterion and the combination of Cohesive Zone Model (CZM) and the bilinear traction-separation law was performed using the MAT-54 material model. At the end of the study, it was determined that the face sheets thickness in sandwich structures had a significant effect on the impact resistance up to a certain impact energy. It has been observed that as the impact velocity gradually increases, there is a decrease in the contact force after a certain threshold value. As the impactor velocity increases, the energy absorption efficiency also increases. It has been determined that the location of the impact is very effective on peak force and energy absorption efficiency. The effect of the number of core layers depends on the face sheets thickness. When the face sheets thickness was not damaged at first contact, the peak force value increased in parallel with the number of layers. It was determined that the dominant damage mode after impact was matrix damage. It has been observed that as the energy level of the impactor increases, damage also occurs on the back surfaces.

Adjacent Buildings Subjected to Seismic Pounding: A systematic Comprehensive Review

Buildings next to one another that are too close together or have differing dynamic properties may vibrate out of phase during earthquakes. This leads to slamming of these buildings against one another. Provision to avoid this pounding effect is given in various codes. When the structures are exposed to external excitation, the dynamic properties of the nearby structures cause the structures to oscillate out of phase. Impacts will happen if the space between the structures is not large enough to support the lateral displacements brought on by this out-of-phase oscillation. The excitation characteristics, the current separation gap size, and the degree of variation between the dynamic properties of the impacting structures all influence the impact forces and impact locations along the heights of the structures. This work provides a detailed investigation of the impact of pounding in both structures that have undergone site-specific analysis and those that have not. If the interaction between the soil and structure is not taken into account during the designing process, the effects of seismic pounding are exacerbated. In addition, this paper analyses a number of research that examine the connection between soil structure and seismic pounding.

Residual behaviour and damage assessment of UHPC-filled double-skin steel tubular columns after lateral impact

Ultra-high performance concrete (UHPC)-filled double-skin steel tubular (DST) column has great potential to be used in the protective structures. Although its lateral impact behaviour has been well understood, the residual behaviour after lateral impact remains unexplored. As a result, this study extensively investigated the residual behaviour and damage assessment of UHPC-filled DST columns after lateral impact. Firstly, a set of six DST columns were designed and tested under lateral impact, followed by static axial compression. In addition, two intact columns were subjected to static axial compression for comparative analysis. Secondly, the refined finite element models were developed and validated using the current test data, and the impact resistant mechanism of UHPC-filled DST columns with different impact locations was analysed. Thirdly, the suitability of different damage indexes for the damage assessment of impacted UHPC-filled DST columns was evaluated. Two damage indexes, the ratio of mid-height deflection to column height (R1), and the ratio of local deflection to the column diameter (R2), were proposed for the DST columns. Finally, two types of machine learning-based models were developed to predict the impact damage of UHPC-filled DST columns. The prediction models were interpreted locally and globally using the additive feature attribution method Shapley Additive Explanation (SHAP). The machine learning-based prediction models can rapidly evaluate the damage extent of impacted UHPC-filled DST column, which hold great significance for the selection of strengthening and retrofitting schemes.

Dynamic response of pile–slab retaining wall structure under rockfall impact

Abstract. Pile–slab retaining walls, as innovative rockfall protection structures, have been extensively utilized in the western mountainous regions of China. With their characteristics of a small footprint, high interception height, and ease of construction, these structures demonstrate promising potential for application in mountainous regions worldwide, such as the Himalayas, Andes, and Alps. However, their dynamic response upon impact and impact resistance energy remain ambiguous due to the intricate composite nature of the structures. To elucidate this, an exhaustive dynamic analysis of a four-span pile–slab retaining wall with a cantilever section of 6 m under various impact scenarios was conducted utilizing the finite-element numerical simulation method. The rationality of the selected material constitutive models and the numerical algorithm was validated by reproducing two physical model tests. The simulation results reveal the following. (1) The lateral displacement of the pile at the ground surface and the concrete damage under the pile at the impact center are greater than those under the slab at the impact center, implying that the impact location has a significant influence on the stability of the structure. (2) There is a positive correlation between the response indexes (impact force, interaction force, lateral deformation of pile and slab, concrete damage) and the impact velocities. (3) The rockfall peak impact force, the ratio of the peak impact force to the peak interaction force, and lateral displacement of the pile at the ground surface had strong linear relationships with rockfall energy. (4) Relative to the bending moment, shear force, and damage degree, the lateral displacement of the pile at the ground surface is the first to reach its limit value. Taking the lateral displacement of the pile at the ground surface as the controlling factor, the estimated maximum impact energy that the pile–slab retaining wall can withstand is 905 kJ in this study when the structure top is taken as the impact point. In cases where the impact energy of falling rocks exceeds 905 kJ, it is recommended to optimize the mechanical properties of the cushion layer, improve the elastic modulus of concrete, increase the reinforcement ratio of longitudinal tension bars, enlarge the section size of piles at ground level, or add anchoring measures to enhance the bending resistance of the retaining structure.

Impact responses of steel–concrete–steel–gradient aluminum foam energy absorbing panels: Experimental and numerical studies

A novel steel–concrete–steel–gradient aluminum foam energy absorbing panel (SCSGF-EAP) has been proposed for improving the impact resistance of existing structures. The impact resistant performances of the SCSGF-EAP were evaluated through the drop weight impact tests and numerical simulations. The varying thickness of gradient aluminum foam and concrete core was considered in the drop weight impact tests. All the specimens presented a consistent failure mode, which included local indentation and global flexure of SCS panel and crushing of gradient aluminum foam. The Finite Element (FE) model was developed through adopting LS-DYNA for studying the impact resistance of SCSGF-EAP, and the comparisons exhibited that numerical results agreed well with experimental data. The internal energy of different components of specimen was determined by numerical model, and the gradient aluminum foam absorbed the majority of the impact energy. Finally, parametric studies were adopted to determine influences of the initial momentum and kinetic energy of impactor, as well as the density of gradient aluminum foam and impact location on the impact response of SCSGF-EAP.

Characteristics of potential head injury situations at the FIFA World Cup Qatar 2022TM.

This exploratory video analysis study aimed to review characteristics of potential head injury situations during a men's professional international football tournament. For 64 matches of the FIFA World Cup Qatar 2022™ FIFA analysts used match footage to record all potential head injury situations. A potential head injury situation was defined as a player staying down for more than 5 s and/or requesting medical attention, and where the body impact location included the player's head. Characteristics were further recorded for match, player (i.e. player action including aerial duels), medical assessment, and outcome (e.g. substitution). Descriptive statistics are reported as well as Pearson's Chi-squared test (or Fisher's exact test) to explore potential head injury situations more likely to result in medical attention. In total, 149 potential head injury situations occurred in 56 matches (mean 2.33/match, range 0-6) involving 117 players. Eight matches resulted in no incidents. Aerial duels were the most frequent match characteristic leading to a potential head injury situation. Injury stoppage with on-pitch medical assessment occurred in 35 of the 149 potential head injury situations (23%), with pitch-side assessment also occurring in 15 situations (10%), resulting in four concussion substitutions. Players were more likely to require medical attention for potential head injuries sustained when the ball was loose (χ2 = 6.88; p = 0.038) when the injured player was jumping (FET p = 0.044) and for head-to-head contact (FET p = <0.001). Further exploration of aerial duels during match play which do and do not lead to potential and actual head injuries is recommended.

‘Mind your head’, tackle characteristics associated with concussions in rugby league: A case-control study

ObjectivesIdentify tackle characteristics associated with concussions in male professional rugby league. DesignCase-control study. MethodsTackles resulting in 196 clinically diagnosed concussions and 6592 non-concussive tackles were analysed, from the men's rugby league Super League between 2018 and 2022. Eleven tackle characteristics were coded for each tackle, and Firth penalised logistic regression models were employed to identify influential variables through forward stepwise selection. Three multivariate models were produced; all (i.e., ball-carrier and tackler), tackler, and ball-carrier concussions. ResultsOf the 196 concussions, 70 % occurred to the tackler and 30 % to the ball-carrier. Initial impact location on the ball-carrier was identified as a predictor in all models, specifically the shorts, upper- and lower-leg (OR 9.1–12.3, compared to shoulder) for tacklers and head/neck (OR 66.1, compared to shoulder) for ball-carriers. Tackler head placement in front of the ball-carrier (OR 8.5, compared to away from the body) and a ball-carrier leading arm in any position (OR 4.8–22.1, compared to no leading arm) provided the greatest odds of a tackler concussion. For player's body position the greatest risk of concussion for all players was observed when both players were falling/diving (OR 8.8, compared to both players upright). One (OR 4.9, compared to two) and four (OR 3.7, compared to two) defender tackles provide the greatest odds for all concussions. ConclusionsConcussion prevention strategies should aim to reduce head impacts by deterring initial contact with the ball-carrier's head/neck. Tackle technique should prioritise making initial impact with the torso and avoid the head being in front of the ball-carrier and any leading arms.

Low-velocity impact of clamped Y-shaped sandwich beams with metal foam core

This study aims to analytically and numerically investigate the dynamic behavior of clamped foam-filled Y-shaped sandwich beams subjected to low-velocity impact. Using the yield criterion for the foam-filled Y-shaped sandwich structure, a theoretical model is proposed. The bound and the analytical solution of low-velocity impact (LVI) of the foam-filled Y-shaped sandwich beam (FYSB) are obtained. Numerical computations are conducted to study the dynamic behavior of FYSB subjected to LVI. Analytical predications are in agreement with numerical. Subsequently, an in-depth analysis is undertaken employing a theoretical model to discuss the influences of parameters such as the Y-shaped plate angle, impact location, foam strength on the dynamic behavior of the FYSB. It is shown that for the given deflection, the impact force diminishes as the impact location progressively approaches the mid-span, and increases with increasing foam strength, Y-shaped plate angle, face-sheet thickness and striker mass. The analytical model can be used to predict the dynamic response of the FYSB subjected to LVI.

Failure mechanism and plastic hinge of RC joints under impact load acting on column ends

Impact loads often act on columns end during accidents such as vehicle impacts and terrorist attacks. The resulting deformations lead to a redistribution of internal forces in the member as well as a reduction in the load carrying capacity. The integrity of the core area of the joint is threatened, which could trigger a progressive collapse. This study numerically investigated the damage and deformation of reinforced concrete (RC) beam-column joints when they are impacted on the column end. The resistance mechanism of joints and the influence of impact location as well as impact velocity was explored. Besides, the deformation capacity of RC beam-column joints under impact loading was quantified using equivalent plastic hinges. It was found that the damage and plastic deformation is concentrated at the impacted column end. The horizontal reaction force at the beam end provides resistance and plays the role as a bearing. The column bottom reaction force is in the same direction as the impact force. However, it is much smaller than the beam end reaction force. The resistance mechanisms within the joints can be categorized into strut-and-tie near the loading point and arches in the mid-span of the beam and column. The core area rotates and has a significant lateral displacement towards the impact location, whether it is loaded at the beam end or the column end. As the impact location moves away from the core aera, the impacted column end exhibit more bending failure. With increasing impact velocity, the impact force, reaction force and total energy absorption of the joint increase. The deformation increases, with more damage occurring in the core area and spreading to the beam. In addition, the plastic curvature was used to describe the actual plastic deformation of the joints, whose maximum occurring at the interface where the impacted column end meets the core area. A formula for the equivalent plastic hinge length of RC joints was proposed, taking into account the effects of impact location and impact velocity.

The Effects of Workplace Spirituality and Self-Efficacy on Quality of Life Among Cancer Survivors: Empirical Quantitative Research.

To investigate the impact of workplace spirituality and self-efficacy (SE) on cancer survivors' quality of life (QOL) and develop nursing interventions. Descriptive survey. Participants were cancer survivors treated at Chung-Ang hospital in Seoul. They were administered a questionnaire covering general and clinical characteristics, workplace spirituality, SE and QOL. Data were analysed using hierarchical multiple regression analyses. Workplace spirituality, SE and QOL were positively correlated. Higher education level, work in the health/medical sector, higher monthly income, undetermined cancer stage or not currently undergoing cancer treatment and absence of physical impairments or comorbidities due to cancer influenced QOL. Regression analysis revealed that SE enhanced QOL. Workplace spirituality and SE correlated with QOL. Notably, SE actively enhanced QOL by providing inner strength regardless of the type of treatment or its physical damage. The findings have practical implications for the development of nursing interventions that aim to boost the confidence and positive assurance of employed cancer survivors in managing their condition and to enhance QOL. Problem addressed: Understanding the impact of workplace spirituality and SE on cancer survivors' QOL. Positive correlations between workplace spirituality, SE and QOL; SE as a primary determinant of QOL. Impact location and population: Relevant to cancer patients managing treatment and work responsibilities, contributing to improved QOL. Adhered to relevant EQUATOR guidelines. No contribution. Not applicable.

Assessing head injury risks in electric scooter accidents: A multi-body simulation study with insights into sex differences

E-scooters have become increasingly popular for short-distance travel in urban areas, but this rise in usage also brings about an increased risk of accidents. Studies have shown that approximately 40% of electric scooter accident victims admitted to hospitals suffer head injuries. Therefore, it is crucial to implement safety measures and improve safety systems and equipment to mitigate these risks. One approach to gaining insights into the injuries users face is through simulations using the multi-body method. This method allows for the reconstruction of accidents by modeling and analyzing the dynamic behavior of interconnected bodies. This study aims to assess the impacts on the user’s head and the injuries they may sustain in electric scooter accidents using numerical methods. Initially, a reference scenario was established based on a YouTube video, with the assumption that the user was an average-height man. Simulations were conducted for various percentiles, including both males and females. Different velocities were simulated to determine the threshold velocity at which survival becomes practically impossible. Two scenarios were considered: one where the car braked for 0.333 s and another where the distance between the start the braking task and the collision was kept constant. The location of the first head impact on the vehicle was also examined. Injury assessment was conducted using two criteria: Head Injury Criterion (HIC) and Brain Injury Criterion (BrIC). The study found that smaller individuals are more vulnerable to severe injuries, and higher car velocities correlate with more severe user injuries. Furthermore, the location of the first impact varies between genders, with women more likely to experience impacts in the lower part of the windshield, while men tend to experience impacts in the central zone. This study highlights the importance of considering user characteristics and accident dynamics in assessing injury risks associated with e-scooters.

ThP4.12 - Impacted Bile Duct Stones Encountered during 1447 Laparoscopic Explorations; Incidence and Management

Abstract Aim To study the incidence and management of impacted bile duct stones encountered during laparoscopic bile duct exploration (LCBDE). Methods A review of patients undergoing LCBDE for impacted stones. Preoperative imaging, operative difficulty grading, impaction location, dis-impaction methods, operative complications and postoperative outcomes were analysed. Results 136 of 1447 (9.4%) LCBDEs had impacted stones; median age 53 years, 63.2% females. 88.2% were emergencies; 94 Jaundiced (69.1%). USS showed CBD dilatation in 30.1%. 16.9% had previous ERCP and 43% previous biliary admissions. CBD exploration was transcystic in 52 (38.2%) and via choledochotomy in 84 (61.8%). LCBDE difficulty grading was IV in 61 (44.9%) and V in 75 (55.1%). The number of stones ranged from 1-70 (mean 6, median 2) and stone size 4-30mm (median 12). All needed choledochoscopy. Impaction was at lower CBD in 83 (61%), Mid-CBD 29 (21.3%), Intra-hepatic 15 (11%), intra and extra hepatic in 6 (4.4%) and intramural in 3. Dis-impaction needed biopsy forceps/grasper fragmentation (45.6%) basket/Fogarty manipulation in 35.3%, laser in 8.8%, pushing stones using the choledocoscope in 6 cases (4.4%) and conversion or leaving stone for ERCP in 7 (5.8% 6 prior to1997). The median operative time was 150 minutes (60-630 minutes). Complications occurred in 33 (24.2%) including15 biliary-related and 9 biliary drain-related. Readmissions occurred in 18 patients (11 biliary-related) and one death was caused by pneumonia. Hospital stay median was 10 days (3 to 54). On 80% follow up the presentation to resolution period median was 2 weeks (1- 30). Conclusions Apart from CBD stones shown on USS and failed ERCP this study identified no obvious risk factors.

Experimental investigation and optimization for after-impact residual strength of a novel gradient corrugated structure

A novel structure based on a gradient corrugated architecture is introduced, and its after-impact residual strength is numerically and experimentally investigated. Low-velocity impact (LVI) and compression after impact (CAI) tests are conducted on designed specimens made of acrylonitrile butadiene styrene (ABS). The experiments reveal that the penetration depth increases linearly with increase in impact energy while the residual strength does not follow the same trend and its degradation rate is decreasing which implies that the structure tends to maintain its strength. A numerical model is developed to simulate the impact and after-impact response of structures with the error range of 2∼15 % for penetration depth values of LVI and less than 5 % error for the residual strength of CAI in comparison with experimental results. In order to maximize the after-impact tolerability, the structural architecture is optimized and realized that trapezoidal cells with decreasing gradient offer the highest specific strength. The sensitivity of the proposed structure to the impact location, with a higher average residual specific resistance, is lower than similar optimized configurations presented in literature.