Contact Area Stress Research Articles

Effect of Velocity and Contact Stress Area on the Dynamic Behavior of the Spinal Cord Under Different Testing Conditions.

Knowledge of the dynamic behavior of the spinal cord under different testing conditions is critical for our understanding of biomechanical mechanisms of spinal cord injury. Although velocity and contact stress area are known to affect external mechanical stress or energy upon sudden traumatic injury, quantitative investigation of the two clinically relevant biomechanical variables is limited. Here, freshly excised rat spinal-cord–pia-arachnoid constructs were tested through indentation using indenters of different sizes (radii: 0.25, 0.50, and 1.00 mm) at various loading rates ranging from 0.04 to 0.20 mm/s. This analysis found that the ex vivo specimen displayed significant nonlinear viscoelasticity at <10% of specimen thickness depth magnitudes. At higher velocity and larger contact stress area, the cord withstood a higher peak load and exhibited more sensitive mechanical relaxation responses (i.e., increasing amplitude and speed of the drop in peak load). Additionally, the cord became stiffer (i.e., increasing elastic modulus) and softer (i.e., decreasing elastic modulus) at a higher velocity and larger contact stress area, respectively. These findings will improve our understanding of the real-time complex biomechanics involved in traumatic spinal cord injury.

ВЛИЯНИЕ НАПРЯЖЕННОГО СОСТОЯНИЯ ТОРМОЗНОГО ДИСКА НА ПАРАМЕТРЫ МИКРОГЕОМЕТРИИ ЕГО ПОВЕРХНОСТИ, НАХОДЯЩЕЙСЯ ВНЕ ОБЛАСТИ КОНТАКТА

The paper shows results of the study dedicated to influence of contact area stress state on a trend of changes for roughness and waviness parameters of brake disc surface located on the periphery of contact with a brake pad in the coverage area of preferred compression and tensile stresses. It also displays that the main trend of surface deformation under the influence of growing mechanical compression stresses consists in increase of altitude and decrease of step parameters of roughness and waviness. The authors have established that in the coverage area of tensile stresses the roughness and the waviness of the brake disk surface returns to initial values determined in condition of absence of external power influence. On the basis of the results, the authors have explained the process of waviness appearance on the brake disc surface. Results of the study are recommended for the application at solving tasks on friction and wear.

Influence of the initial hydrostatic pressure on contact area coefficient under drainage condition

The expression of effective stress proposed by Terzaghi has always been questioned. Many correction formulas are modification of pore pressure term. The pore pressure factor is related to porosity, contact area and other factors. When the particles are in point contact, the expression of the effective stress is that proposed by Terzaghi, while for the surface contact particles, the actual effective stress increases the stress produced by pore pressure passing through the contact surface based on the Terzaghi effective stress. There are many factors that affect the development of contact area and pore pressure, therefore, a series of the drained triaxial tests were carried out on four groups of sand samples with different initial hydrostatic pressures to study the influence of different initial hydrostatic pressures on the effective stress due to the term of contact area (σα). The test results show that the shear strength is increases with the initial hydrostatic pressure under the same effective confining pressure, which indirectly indicates that the initial hydrostatic pressure increases the contact area stress.

The Role of Counter-Face Roughness on the Tribological Performance of a Clutch System Tested with a Pin-On-Disc Tribometer

This study was a continuous investigation of the roles played by the tribofilm on dry automotive clutch system performance. Tribological experiments were performed by the addition of wear debris at the beginning of tribometer tests and by reducing the surface roughness of a cast iron counter-face. The initial surface conditions of cast discs were 0.2 and 1.2 µm. The pin-on-disc tests were carried out at three different PV levels: 3.08, 7.88, and 10.09 MPa·ms−1, and the current results were correlated to those previously obtained in the standard tribometer procedure. When the wear debris was added into the tribosystem, the friction coefficient level dropped drastically while the assembly wear rate rose. In contrast, the modified cast discs provided a reduced wear rate of assembly and a higher and more stable friction coefficient level. These improvements were obtained in a severe condition where higher temperature levels were reached. For the tests with added debris, SEM observations revealed a more intense tribofilm development over the worn surfaces of the clutch friction material. The smoothest cast disc did not damage the developed tribofilms and maintained them more stably due to a reduction in contact area stresses at the highest tribometer test.

The Effect of Tibial Posterior Slope on Contact Force and Ligaments Stresses in Posterior-Stabilized Total Knee Arthroplasty-Explicit Finite Element Analysis

PurposeThe purpose of this study is to evaluate the effect of change in tibial posterior slope on contact force and ligament stress using finite element analysis.Materials and MethodsA 3-dimensional finite element model for total knee arthroplasty was developed by using a computed tomography scan. For validation, the tibial translations were compared with previous studies. The finite element analysis was conducted under the standard gait cycle, and contact force on ultra-high molecular weight polyethylene (UHMWPE) and stresses on lateral and medial collateral ligaments were evaluated.ResultsThe tibial translations showed similarity with previous studies. As the tibial posterior slope angle increases, the contact stress area increased and was well distributed, and the contact force on UHMWPE decreased overall. However, the maximum contact force in the case for 10° case was greater than those for others. The stresses on ligaments were the greatest and smallest in 0° and 10° cases, respectively.ConclusionsThe higher tibial posterior slope angle leads to the lower contact stress and more extensive stress distribution overall in posterior-stabilized total knee arthroscopy. However, it does not absolutely mean the smallest contact force. The stresses on ligaments increased with respect to the smaller tibial posterior slope angle.

Contact Forces in Non-bonded Pavement Materials

We have studied macroscopic stress distributions in horizontal and vertical directions in non-bonded aggregates, as well as the contact forces (local stresses) at the contact areas (microscopic'). A ring chamber was used to study the horizontal and vertical stresses under static vertical loads, whereas contact area stresses were measured using pressure film placed in different parts of the equipment. The pressure films reveal elevated contact forces at some contact areas in response to the applied load, and the grain size range of the particles also influences the stress (contact force) distribution: fine-grained aggregates distribute forces more evenly than coarse-grained aggregates. When an open fraction of aggregates is used, the coarse-grained aggregates have a greater role in supporting loads, as higher contact forces are transmitted across contact areas between large aggregate particles.

Contact Forces in Non-bonded Pavement Materials

ABSTRACT We have studied macroscopic stress distributions in horizontal and vertical directions in non-bonded aggregates, as well as the contact forces (local stresses) at the contact areas (“microscopic”). A ring chamber was used to study the horizontal and vertical stresses under static vertical loads, whereas contact area stresses were measured using pressure film placed in different parts of the equipment. The pressure films reveal elevated contact forces at some contact areas in response to the applied load, and the grain size range of the particles also influences the stress (contact force) distribution: fine-grained aggregates distribute forces more evenly than coarse-grained aggregates. When an open fraction of aggregates is used, the coarse-grained aggregates have a greater role in supporting loads, as higher contact forces are transmitted across contact areas between large aggregate particles.

CONTACT STRESS AREA MEASUREMENT OF SPHERICAL FRUIT

This paper aims to measure the contact area of rubber spheres and oranges compressed against parallel rigid and flat plates. To measure this area a system composed of a transducer, an interface device and a microcomputer was used. The transducer is composed of a board on which some micro-switches were disposed in a linear and radial direction spaced 0.5 mm from each other. As the contact area was expanding, the micro-switches connected to the interface turned on, forming the bits that compose the binary word that measures the diameter of the area. The data acquisition system is in-charge of recording the measured area, as function of the deformation imposed to the spheres and to the orange fruit. The obtained area as a function of deformation was compared with the data reported by Linares, 1996.