Interlaminar stresses that arise in composite laminates where gradients exist in in-plane stress fields are investigated. Two distinct mechanisms give rise to interlaminar stresses in generic problems, the presence of free edges and in-plane gradients. It is shown that the latter mechanism should be considered separately from the former and that interlaminar stresses from such in-plane gradients can be significant. A methodology to approximate these stresses through direct integration of the equilibrium equations is presented. The methodology involves the use of closed-form expressions of the in-plane stress field obtained by solving two-dimensional elasticity problems using homogenized material properties. As an example, the methodology is applied to the case of a laminate with a circular hole through which the importance of interlaminar stresses from in-plane gradients is demonstrated. The results show that the characteristics of the interlaminar stresses from in-plane gradients are very different from those of interlaminar stresses arising from free edges. Specifically, the parameters that affect the decay rates and magnitudes of the interlaminar stresses from the two mechanisms are found to be different. The current investigation provides new insights into interlaminar stress problems, in general, and offers a simple method for calculating the interlaminar stresses due to in-plane gradients.

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Crack initiation and growth behavior in solder joints under cyclic shear deformation using piezomechanical actuation have been investigated. Experiments were conducted on specimens that consist of piezo–ceramic plates and eutectic Sn–Pb solder bonded in a double-lap shear configuration. Specimens were tested under various frequencies and ranges of applied electric field at room temperature, and a shear-lag model using elastic–perfectly plastic solder properties was developed to characterize the mechanical response of the solder joint. Nominal plastic shear strain ranges from 0.182% to 2.69% were considered. The applied shear strains measured using digital image correlation showed agreement with shear strains from analyses. The Coffin–Manson relationship was used to characterize crack initiation, and a power law was employed for crack growth. This work shows that the fatigue characteristics of solder joints using piezomechanical actuation exhibit reasonable agreement with those using other types of testing methods and provides the framework for a new accelerated testing methodology for solder joint reliability.

Background: A lateral tilt position can affect the size of the femoral vein (FV) due to increased venous blood volume in the dependent side of the body.Methods: Forty-two patients, aged 20-60 years, were enrolled in this study. The crosssectional area (CSA), anteroposterior, and transverse diameters of the FV were measured 1 cm below the left inguinal line using ultrasound. The value of each parameter was recorded in the following four positions: (1) supine, (2) supine + 10° left-lateral tilt (LLT), (3) 10° reverse Trendelenburg (RT), and (4) RT + LLT.Results: CSAs of the left FV in the supine, supine + LLT, RT, RT + LLT positions were 0.93 ± 0.22, 1.11 ± 0.29, 1.17 ± 0.29, and 1.31 ± 0.32 cm 2 , respectively. Compared to the supine position, there was a significant increase in CSA and anteroposterior diameter according to the three changed positions. The transverse diameter of the left FV was significantly increased in supine + LLT, RT, RT + LLT positions compared to that in the supine position (P = 0.010, P = 0.043, P = 0.001, respectively). There was no significant difference in the transverse diameter of the left FV between the supine + LLT and RT positions (P = 1.000).Conclusions: Adding LLT to the supine and RT positions increased the CSA of the unilateral FV significantly.